APR. 2001TECHNICAL INFORMATION

PHOTON COUNTINGUsing Photomultiplier Tubes

INTRODUCTION

Recently, non-destructive and non-invasive measurementusing light is becoming more and more popular in diversefields including biological, chemical, medical, materialanalysis, industrial instruments and home appliances.Technologies for detecting low level light are receiving par-ticular attention since they are effective in allowing highprecision and high sensitivity measurements withoutchanging the properties of the objects.Biological and biochemical examinations, for example, uselow-light-level measurement by detecting fluorescenceemitted from cells labeled with a fluorescent dye. In clini-cal testing and medical diagnosis, techniques such as in-vitro assay and immunoassay have become essential forblood analysis, blood cell counting, hormone inspectionand diagnosis of cancer and various infectious diseases.These techniques also involve low-light-level measurementsuch as colorimetry, absorption spectroscopy, fluorescencephotometry, and detection of l ight scattering orIuminescence measurement. In RIA (radioimmunoassay)which has been used in immunological examinations us-ing radioisotopes, radiation emitted from a sample is con-verted into low level light which must be measured withhigh sensitivity. In biological application, precise detectionof the receptor gene expression is becoming important.The reporter genes are labeled with fluorescence or chemi-luminescence substances to give off light at expression.Photomultiplier tubes, photodiodes and CCD image sen-sors are widely used as “eyes” for detecting low level light.These detectors convert light into analog electrical sig-nals (current or voltage) in most applications. However,when the light level becomes weak so that the incidentphotons are detected as separate pulses, the single pho-ton counting method using a photomultiplier tube is veryeffective if the average time intervals between signal pulsesare sufficiently wider than the time resolution of the photo-multiplier tube. This photon counting method is superiorto analog signal measurement in terms of stability, detec-tion efficiency and signal-to-noise ratio.This technical manual explains how to use photomultipliertubes in photon counting to perform low-light-level mea-surement with high sensitivity and high accuracy. Thismanual also describes the principle of photon counting,its key points and operating circuit configuration, as wellas characteristics of photomultiplier tubes and their selec-tion guide.

TABLE OF CONTENTS

1. What is Photon Counting ? ............................................... 21-1 Analog Mode and Digital Mode (Photon Counting Mode)1-2 The Principle of Photon Counting

2. Operation and Characteristics of Photon Counting ........ 52-1 Photon Counter and Multichannel Pulse Height Analyzer2-2 Basic Characteristics in Photon Counting

(1) Pulse Height Distribution and Plateau Characteristics(2) Output Instability vs. Variations in Photomultiplier Tube

Gain (current amplification)(3) Linearity of Count Rate

3. Characteristics of Photomultiplier Tubes ......................... 93-1 Spectral Response (Quantum Efficiency)3-2 Collection Efficiency3-3 Supply Voltage and Gain3-4 Noise3-5 Magnetic Shield3-6 Stability and Dark Storage3-7 Uniformity3-8 Signal-to-Noise Ratio

4. Measurement Systems ....................................................... 164-1 Synchronous Photon Counting Using Chopper4-2 Time-Resolved Photon Counting by Repetitive Sampling4-3 Time-Resolved Photon Counting by Multiple Gates4-4 Time-Correlated Photon Counting

5. Selection Guide ................................................................... 185-1 Selecting the Photomultiplier Tube5-2 Photomultiplier Tubes for Photon Counting5-3 Related Products

2

Figure 1 : Output Pulses from Photomultiplier Tube at Different Light Levels

1-2 The Principle of PhotonCounting

One important factor in photon counting is the quantumefficiency (QE). It is the production probability of photo-electrons being emitted when one photon strikes the pho-tocathode. In the single photoelectron state, the numberof emitted photoelectrons (primary electrons) per photonis only 1 or 0. Therefore QE refers to the ratio of the aver-age number of emitted electrons from the photocathodeper unit time to the average number of photons incidenton the photocathode.

Figure 2 : Photomultiplier Tube Operationin Single Photoelectron State

1. What is Photon Counting ?

1-1 Analog Mode and Digital Mode(Photon Counting Mode)

A photomultiplier tube (PMT) consists of a photocathode,an electron multiplier (composed of several dynodes) andan anode. (See Figure 2 for schematic construction.) Whenlight enters the photocathode of a photomultiplier tube,photoelectrons are emitted from the photocathode. Thesephotoelectrons are multiplied by secondary electron emis-sion through the dynodes and then collected by the an-ode as an output pulse. In usual applications, these out-put pulses are not handled as individual pulses but dealtwith as an analog current created by a multitude of pulses(so-called analog mode). In this case, a number of pho-tons are incident on the photomultiplier tube per unit timeas in of Figure 1 and the resulting photoelectrons areemitted from the photocathode as in . The photoelec-trons multiplied by the dynodes are then derived from theanode as output pulses as in . At this point, when thepulse-to-pulse interval is narrower than each pulse widthor the signal processing circuit is not fast enough, the ac-tual output pulses overlap each other and eventually canbe regarded as electric current with shot noise fluctua-tions as shown in .In contrast, when the light intensity becomes so low thatthe incident photons are separated as shown in , theoutput pulses obtained from the anode are also discreteas shown in . This condition is called a single photo-electron state. The number of output pulses is in directproportion to the amount of incident light and this pulsecounting method has advantages in signal-to-noise ratioand stability over the analog mode in which an average ofall the pulses is made.This pulse counting technique is known as the photoncounting method. Since the detected pulses undergo bi-nary processing for digital counting, the photon countingmethod is also referred to as the digital mode.

ARRIVAL OF PHOTONS

LOWER LIGHT LEVEL (Single Photoelectron State)

HIGHER LIGHT LEVEL (Multiple Photoelectron State)

PHOTOELECTRON EMISSION

SIGNAL OUTPUT (PULSES)

SIGNAL OUTPUT (PULSE OVER LAPPED)

ARRIVAL OF PHOTONS

PHOTOELECTRON EMISSION

SIGNAL OUTPUT(DISCRETE PULSES)

TIME

TPHOC0027EB

TIME

ARRIVAL OF PHOTONS

LOWER LIGHT LEVEL (Single Photoelectron State)

HIGHER LIGHT LEVEL (Multiple Photoelectron State)

PHOTOELECTRON EMISSION

SIGNAL OUTPUT (PULSES)

SIGNAL OUTPUT (PULSE OVER LAPPED)

ARRIVAL OF PHOTONS

PHOTOELECTRON EMISSION

SIGNAL OUTPUT(DISCRETE PULSES)

TIME

TPHOC0027EB

TIME

PHOTOCATHODE

Dy1 Dy2 Dyn-1 Dyn

P

1ST DYNODE

SINGLEPHOTONS

ELECTRONGROUPS

ANODE

TPMOC0048EB

PULSEHEIGHT

3

Photoelectrons emitted from the photocathode are accel-erated and focused onto the first dynode (Dy1) to producesecondary electrons. However, some of these electronsdo not strike the Dy1 or deviate from their normal trajecto-ries, so they are not multiplied properly. This efficiency ofcollecting photoelectrons is referred to as the collectionefficiency (CE). In addition, the ratio of the count value(the number of output pulses) to the number of incidentphotons is called the detection efficiency or counting effi-ciency, and is expressed by the following equation :

Detection efficiency =Nd / Np = h ¥ a

where Nd is the count value, Np is the number of incidentphotons, h is the photocathode QE and a is the CE. Al-though it will be discussed later, detection efficiency alsodepends on the threshold level that brings the output pulsesinto a binary signal. Since the number of secondary elec-trons emitted from the Dy1 varies from several to about20 in response to one primary electron from the photo-cathode, they can be treated by Poisson distribution ingeneral, and the average number of secondary electronsbecomes the secondary electoron emission ratio d . Thisholds true for multiplication processes in the subsequentdynodes. Accordingly, for a photomultiplier tube having nstages of dynodes, a single photoelectron from the photo-cathode is multiplied by d n to create a group of electronsand is derived from the anode as an output pulse. In thisprocess, the height of each output pulse obtained at theanode depends on fluctuations in the secondary electronmultiplication ratio stated above, so that it differs from pulseto pulse. (Figure 3)Other reasons why the output pulse height becomes un-equal are that gain varies with the position on each dyn-ode and some deviated electrons do not contribute to thenormal multiplication process. Figure 3 shows a histogramof the anode pulse heights. This graph is known as thepulse height distribution (PHD).As illustrated in Figure 3, the photomultiplier tube outputexhibits fluctuations in the pulse height and the PHD isobtained by time-integrating these output pulses at differ-ent pulse heights. The abscissa of this graph indicates thepulse height that represents the charge (number of elec-trons contained in one electron group) or the pulse volt-age (current) produced by that electron group. It is gener-ally expressed in the number of channels used for the ab-scissa of a multichannel analyzer.

Figure 3 : Photomultiplier Tube Output and PHD

TIM

EC

OU

NT

S A

T E

AC

HP

ULS

E H

EIG

HT

PULSE HEIGHTS (CHARGES)TPMOC0049EB

LOW

CO

UN

TF

RE

QU

EN

CY

HIG

H C

OU

NT

FR

EQ

UE

NC

Y

LOW

CO

UN

TF

RE

QU

EN

CY

Photomultiplier Tube Output in SinglePhotoelectron State

The output signal from a photomultiplier tube in the pho-ton counting mode can be calculated as follows:In the photon counting mode, a single photoelectron e-

(electron charge:1.6 ¥ 10-19 C) is emitted from the pho-tocathode. If the photomultiplier tube gain m is5 ¥ 106, then the anode output charge is given by

e ¥ m = 1.6 ¥ 10-19 ¥ 5 ¥ 106 C= 8 ¥ 10-13 C

Here, if the pulse width t (FWHM) of the anode outputsignal is 10 ns, then the output pulse peak current Ip is

Ip = e ¥ m ¥ 1/t A= (8 ¥ 10-13) C /(10 ¥ 10-9) s= 80 m A

This means that the anode output pulse width is nar-rower, we can obtain much higher output peak current.If the load resistance or input impedance of the suc-ceeding amplifier is 50 W , the output pulse peak volt-age Vo becomes

Vo = Ip ¥ 50 W= 4 mV

The amplitude of the photomultiplier tube output pulsein the photon counting mode is extremely small. Thisrequires a photomultiplier tube having a high gain andmay require an amplifier with sufficiently low noise rela-tive to the photomultiplier tube output noise. As a gen-eral guide, photomultiplier tubes should have a gain ofapproximately 1 ¥ 106 or more.

4

Figure 4 (a) shows a PHD when the incident light level isincreased under single photoelectron conditions, and (b)shows a PHD when the supply voltage is changed.

The ordinate is the frequency of the output pulses thatproduce a certain height within a given time. Therefore,the distribution varies with the measurement time or thenumber of incident photons in the upper direction of theordinate as shown in Figure 4 (a).As explained above, the abscissa of the PHD representsthe pulse height and is proportional to the gain of the pho-tomultiplier tube and becomes a function of the supplyvoltage of the photomultiplier tube. This means that as thesupply voltage changes, the PHD also shifts along theordinate, but the total number of counts is almost con-stant.

Figure 4 : PHD Characteristics

CO

UN

TS

(a) When the incident light level is increased

SIGNAL+NOISE

PULSE HEIGHT

INCREASE IN LIGHT INTENSITY

CO

UN

TS

PULSE HEIGHT (b) When the supply voltage is changed TPHOB0032EB

SUPPLY VOLTAGE TOPHOTOMULTIPLIER TUBE

INCREASE IN

5

2. Operation and Characteristics of Photon Counting

This section describes circuit configurations for use inphoton counting and the basic characteristics of photoncounting measurements.

2-1 Photon Counter andMultichannel Pulse HeightAnalyzer

There are two methods of signal processing in photoncounting: one uses a photon counter and the other a mul-tichannel pulse height analyzer (MCA). Figure 5 showsthe circuit configuration of each method and the pulseshapes obtained from each circuit system.In the photon counter system of Figure 5 (a), the outputpulses from the photomultiplier tube are amplified by thepreamplifier. These amplified pulses are then directed intothe discriminator. The discriminator compares the inputpulses with the preset reference voltage to divide theminto two groups: one group is lower and the other is higherthan the reference voltage. The lower pulses are elimi-nated by the lower level discriminator (LLD) and in some

Figure 5 : Typical Photon Counting Systems

cases, the higher pulses are eliminated by the upper leveldiscriminator (ULD). The output of the comparator takesplace at a constant level (usually a TTL level from 0 V to 5V, or an ECL level of –0.9 V to –1.7 V for high-speed out-put). The pulse shaper forms rectangular pulses allowingcounters to count the discriminated pulses.In contrast, in the MCA system shown in Figure 5 (b), theoutput pulses from the photomultiplier tube are generallyintegrated through a charge-sensitive amplifier, amplifiedand shaped with the linear amplifier. These pulses are dis-criminated according to their heights by the discriminatorand are then converted from analog to digital. They arefinally accumulated in the memory and displayed on thescreen. This system is able to output pulse height infor-mation and frequency (the number of counts) simulta-neously, as shown in the figure.The photon counter system is used to measure the num-ber of output pulses from the photomultiplier tube corre-sponding to incident photons, while the MCA system isused to measure the height of each output pulse and thenumber of output pulses simultaneously. The former sys-tem is superior in counting speed and therefore used forgeneral-purpose applications. The MCA system has thedisadvantage in not being able to measure high counts, itis used for applications where pulse height analysis is re-quired.

ULD

TTL LEVELLLD

ULDLLD

ULDLLD

(a) Photon counter system

(b) MCA system

PHOTONS

PHOTONS

PREAMPLIFIER COUNTER

MEMORYDISPLAY

A/D CONVERTERLINEAR AMPLIFIERPULSE SHAPER

DISCRIMINATOR

CHARGESENSITIVE AMP.

DISCRIMINATOR

PHOTOMULTIPLIERTUBE PULSE SHAPER

ACCUMULATION

=50 s

ULD

LLD

TPHOC0028EB

PHOTOMULTIPLIERTUBE PREAMPLIFIER

CO

UN

TS

TIM

E

PULSE HEIGHTmt

6

2-2 Basic Characteristicsin Photon Counting

(1) Pulse Height Distribution andPlateau Characteristics

Figure 6 shows pulse height distributions (PHD) of a pho-tomultiplier tube, obtained with an MCA. The curve (a) isthe output when signal light is incident on the photomulti-plier tube, while the curve (b) represents the noise whensignal light is removed. The major noise component re-sults from thermionic emission from the photocathode anddynodes. The PHD of such noise usually appears on thelower pulse height side. These PHD are the so-called dif-ferential curves and the lower level discrimination (LLD) isusually set at the valley of the curve (a). To increase de-tection efficiency, it is advantageous to set the LLD at alower position, but this is also accompanied by a noiseincrease.In contrast to the curve (a) in Figure 6, the curve (c) showsan integration curve in which the total number of pulseshigher than a certain discrimination level have been plot-ted while changing the discrimination level. Since this in-tegration curve (c) has an interrelation with the differentialcurve (a), the proper discrimination levels can be set inthe photon counter system without using an MCA, by ob-taining the integration curve instead.

The LLD stated above corresponds to a pulse height on agentle slope portion in the integration curve. But this is notso distinct from other portions, making it difficult to deter-mine the LLD. Another method using plateau characteris-tics is more commonly used. By counting the number ofpulses with the LLD fixed while varying the supply voltageto the photomultiplier tube, a curve similar to the"SIGNAL+NOISE" curve shown in Figure 7 can be plot-ted. Although, analog gain increases expotentially withsupply voltage, since the photomultiplier tube counts onlythe number of pulses, the slope of the curves is relativelyflat, which makes the supply voltage setting easier. Thesecurves are known as the plateau characteristics. The sup-ply voltage for the photomultiplier tube should be set withinthis plateau region. It is also clear that plotting the signal-to-noise ratio shows a plateau range in the same supplyvoltage range. (See Section 3-8 (2).)

Figure 7 : Plateau Characteristics

Figure 6 : Differential and Integral Displays of PHD

PULSE HEIGHT (ch)

NOISE/DIFFERENTIAL (b)VALLEY

SIGNAL/DIFFERENTIAL (a)

PEAK

SIGNAL/INTEGRAL (c)

CO

UN

TS

(IN

TE

GR

AL)

CO

UN

TS

/CH

AN

NE

L (D

IFF

ER

EN

TIA

L)

1

0 200 400 600 800 1000

2

2

0

4

6

8

103(×106) (×103)

TPHOB0033EC

LLD

800 900 1000 1100 1200 1300 1400 15007000

1000

2000

4000

3000

6000

5000

7000

CO

UN

T R

AT

E (

s-1)

S/N

RA

TIO

PHOTOMULTIPLIER TUBE SUPPLY VOLTAGE (V)

NOISE

SIGNAL+NOISE

PLATEAU RANGE

S/N RATIO

TPHOB0034EB

HIGH VOLTAGE SETTING

800 900 1000 1100 1200 1300 1400 15007000

1000

2000

4000

3000

6000

5000

7000

CO

UN

T R

AT

E (

s-1)

S/N

RA

TIO

PHOTOMULTIPLIER TUBE SUPPLY VOLTAGE (V)

NOISE

SIGNAL+NOISE

PLATEAU RANGE

S/N RATIO

TPHOB0034EB

HIGH VOLTAGE SETTING

7

0.5

1.0

1.5

0600 700 800 900 1000 1100 1200

CO

UN

T R

AT

E (

106 s-1

)

SUPPLY VOLATGE (V)

A

B

VC

VC'

VHVL

TPHOB0038EA

PLATEAU RANGE

(2) Output Instability vs. Variationsin Photomultiplier Tube Gain

If the photomultiplier tube gain varies for some reason (forexample, a change in supply voltage or fluctuations in theambient temperature, etc.), the output current of the pho-tomultiplier tube is also affected and exhibits variations. Inthe analog mode the output current (or gain) of the photo-multiplier tube changes with variations in the supply volt-age as shown in Figure 8 (a). In the photon counting mode,the output count changes, but this is significantly smallerthan in the analog mode.By setting the supply voltage in the plateau region as shownin Figure 7, the photon counting mode can minimizechanges in the count rate with respect to variations in thesupply voltage, without sacrificing the signal-to-noiseratio. This means that the photon counting mode ensureshigh stability even when the gain of the photomultipliertube varies, as the gain is a function of the supply voltage.For the above reasons, the photon counting mode offers

several times higher stability than the analog mode ver-sus variations in the operating conditions.

Figuer 8 : Output Variation vs. Supply Voltage

RELATIVE SUPPLY VOLTAGE

0.96 0.98 1.00

1.0

1.2

1.4

1.6

1.8

2.0

2.2

1.02 1.04 1.06 1.08 1.10

CH

AN

GE

RA

TE O

F C

OU

NTS

(PH

OTO

N C

OU

NTI

NG

MO

DE

)C

HA

NG

E R

ATE

OF

GA

IN (A

NA

LOG

MO

DE

)

ANALOG MODE (a)

PHOTON COUNTING MODE (b)

TPHOB0035EA

Speaking it in a broad sence, the integration curve ex-plained in Section 2-2 (1) has plateau characteristics.Here we describe a more practical method for obtainingthe plateau characteristics by varying the photomultipliertube supply voltage.1. Set up the photomultiplier tube, photon counter, high-

voltage power supply, dark box, light source, etc, re-quired to perform photon counting. Preferably, the pho-tomultiplier tube should be stored in the dark box forabout one hour after the setup has been completed.

2. Set the discrimination level (LLD) according to the in-struction manual for the photon counter being used.Then allow a very small amount of light to strike thephotomultiplier tube.

3. Gradually increase the photomultiplier tube supplyvoltage starting from about 500 V. When the photoncounter begins to count any signal, halt there and makea plot of the supply voltage (VL) and the counted valueat that point, on a graph with the abscissa showingthe supply voltage and the ordinate representing thecount rate.

4. Increase the supply voltage with a 50 V step until itreaches about 90 % (VH) of the maximum supply volt-age while making plots on the graph. This will createa curve like "A" shown in Figure 9.

How to Obtain the Plateau5. With the photomultiplier tube operated at a voltage

(Vc) in the middle of the flat portion of curve "A", ad-just the light source intensity so that the counted valueis set to 10 % to 30 % of the maximum count rate ofthe photon counter.

6. Readjust the photomultiplier tube supply voltage toset at VL, then make fine plots while changing thephotomultiplier tube supply voltage in 10 V or 20 Vsteps. This will make a curve like "B" shown in Fig-ure 9.

7. In the flat range (plateau range) on curve "B", thevoltage Vc' at a point where the differential coeffi-cient is smallest (minimum slope) will be the opti-mum PMT operating voltage.

Figure 9 : Plotting Plateau characteristics

8

(3) Linearity of Count Rate

The photon counting mode is generally used in very low-light-level regions where the count rate is low, and exhib-its good linearity. However, when the amount of incidentlight becomes large, it is necessary to take the linearity ofthe count rate into account. The upper limit of the band-width of photomultiplier tubes ranges from 30 MHz to300 MHz for periodical signal. Therefore, the maximumcount rate in the photon counting mode where randomphotos enter the photomultiplier tube is determined by thetype of photomultiplier tube and the time resolution of thesignal processing circuit connected to the photomultipliertube. The time resolution referred to here is defined as theminimum time interval between successive pulses that canbe counted as separate pulses.Figure 10 shows a typical linearity of the count rate ob-tained from a Hamamatsu H6180-01 Photon CountingHead. As can be seen from the figure, the dynamic rangereaches as high as 107 s-1. In this case, the linearity of thecount rate is limited by the time resolution (pulse pair reso-lution) of the built-in circuit (18 ns).If we let the measured count rate be N' (s-1) and the timeresolution be t (s), the real count rate N (s-1) can be ap-proximated as follows:

Figure 11 shows the actual data measured with the H6180-01 Photon Counting Head, along with the corrected dataobtained with the above equation. This proves that aftermaking correction, the photon counting mode provides anexcellent linearity with a count error of less than 1 %, evenat a high count rate of 107 s-1.

N '1–N't

N =

Figure 10 : Linearity of Count Rate

Figure 11 : Correction of Count Rate Linearity

102101

102

103

105

104

106

107

108

104103 105 107106 108 109

CO

UN

T R

AT

E(s

-1)

INCIDENT NUMBER OF PHOTONS (s-1)

TPHOB0036EB

103

+10 %

0 %

-10 %

-20 %104 105 106 107

DE

VIA

TIO

N

COUNTS (s-1)

CORRECTED

MEASURED

TPHOB0037EA

9

3. Characteristics of Photomultiplier Tubes

3-1 Spectral Response(Quantum Efficiency )

When N number of photons enter the photocathode of aphotomultiplier tube, the N × quantum efficiency (QE) ofphotoelectrons on average are emitted from the photo-cathode. The QE depends on the incident light wavelengthand so exhibits spectral response.Figures 12 (a) and (b) show typical spectral response char-acteristics for various photocathodes and window materi-als. The spectral response at wavelengths shorter than350 nm is determined by the window material used, asshown in Figure 13.In general, spectral response characteristics are expressedin terms of cathode radiant sensitivity or QE. The QE and

Figure 12 : Typical Spectral ResponseCharacteristics

radiant sensitivity have the following relation at a givenwavelength.

where S is the cathode radiant sensitivity in amperes perwatt (A/W) at the given wavelength λ in nanometers.

3-2 Collection Efficiency

The collection efficiency (CE) is the probability in percent,that single photoelectrons emitted from the photocathodecan be finally collected at the anode as the output pulsesthrough the multiplication process in the dynodes. In par-ticular, the CE is greatly affected by the probability thatthe photoelectrons from the photocathode can enter thefirst dynode. Generally, the CE is from 70 % to 90 % forhead-on photomultiplier tubes and 50 % to 70 % for side-on photomultiplier tubes with full cathode illumination.The CE is very important in photon counting measure-ment. The higher the value of the CE, the smaller the sig-nal loss, thus resulting in more efficient and accurate mea-surements. The CE is determined by the photocathodeshape, dynode structure and voltage distribution for eachdynode.As stated earlier, the ratio of the number of signal pulsesobtained at the anode to the number of photons incidenton the photocathode is referred to as the detection effi-ciency or counting efficiency.

MgF2

100 120 160 200 240 300 400 500

100

10

1

TR

AN

SM

ITT

AN

CE

(%

)

WAVELENGTH (nm)

BOROSILICATEGLASSUV

TRANSMITTINGGLASS

SYNTHETICSILICA

TPMOB0053EA

QE= S ×1240

Figure 13 : Typical Transmittance of Window Materials

Figure 12(a): Transmission Mode Photocathodes

1.0

0.1

0.01

10

100

100 200 300 400 500 600 700 800 1000 1200

QU

AN

TU

M E

FF

ICIE

NC

Y (

%)

MULTIALKALI

WAVELENGTH (nm)

BOROSILICATE GLASSUV GLASS

TPMOB0083EA

Figure 12(b): Reflection Mode Photocathodes

1.0

0.1

0.01

10

100

100 200 300 400 500 600700 800 1000 1200

TPMOB0084EA

InGaAs

BOROSILICATE GLASSUV GLASSSYNTHETIC SILICA

GaAsMULTIALKALI

BIALKALI

QU

AN

TU

M E

FF

ICIE

NC

Y (

%)

WAVELENGTH (nm)

BIALKALI

EXTENDED-REDMULTIALKALI

Ag-O-Cs

10

Figure 14 shows the relation between the CE and the pho-tocathode to first dynode voltage of 28 mm (1-1/8 ") diam-eter photomultiplier tubes, measured in the photon count-ing mode with the discrimination level kept constant andwith small area illumination. As can be seen, the CE sharplyvaries at voltages lower than 100 V, but becomes satu-rated and shows little change when the voltage exceedsthis. This means that a sufficient voltage should be ap-plied across the photocathode and the first dynode to ob-tain stable CE.

Figure 14 : CE vs. Photocathode to First Dynode Voltage

3-3 Supply Voltage and Gain

The output pulse height of a photomultiplier tube varieswith the supply voltage change, even when the light levelis kept constant. This means that the gain of the photo-multiplier tube is a function of the supply voltage. The sec-ondary emission ratio δ is the function of voltage E be-tween dynodes and is given by

δ = A • Eα

where A is the constant and α is determined by the struc-ture and material of the electrodes, which usually takes avalue of 0.7 to 0.8.Here, if we let n denote the number of dynodes and as-sume that the δ of each dynode is constant, then thechange in the gain µ relative to the supply voltage V isexpressed as follows:

(K is a constant.)Since typical photomultiplier tubes have 9 to 12 dynodestages, the output pulse height is proportional to the 6th to10th power of the supply voltage. The curve previouslyshown in Figure 8 for the analog mode represents thischaracteristic.

Figure 15 : Gain vs. Supply Voltage

Figure 16 shows the relation between the secondaryelectorn emission ratio (δ 1) and the photocathode to firstdynode voltage. The incident light is passed through a slitof 3 mm × 15 mm for side-on photomultiplier tubes, or isfocused on a spot of 10 mm diameter for head-on photo-multiplier tubes. It is clear that the secondary electron emis-sion ratio depends on the material of the secondary elec-tron emission surface. Generally, the larger the second-ary electron emission ratio, the better the PHD will be.

Figure 16 : Secondary Electron Emission Yield vs.Supply Voltage

0

5

10

15

100 200

SIDE-ON:BIALKALI (SECONDARY PHOTOEMISSIVE SURFACE)

SIDE-ON:MULTIALKALI (SECONDARY PHOTOEMISSIVE SURFACE)

HEAD-ON:BIALKALI (LINE DYNODE) (SECONDARY PHOTOEMISSIVE SURFACE)

SIDE-ON:SLIT (3 mm × 15 mm)INCIDENT LIGHT

HEAD-ON:SPOT ( 10 mm)

SE

CO

ND

AR

Y E

LEC

TR

ON

EM

ISS

ION

YIE

LD :

1

PHOTOCATHODE TO FIRST DYNODE VOLTAGETPMOB0085EA

δ φ

0 50 100 150 2000

20

40

60

80

100

CE

(%)

PHOTOCATHODE TO FIRST DYNODE VOLTAGE (V)

TPMOB0057EB

φ

φφ

28 mm SIDE-ON TYPE(3 mm × 15 mm LIGHT SLIT)

28 mm HEAD-ON TYPE( 10 mm LIGHT SPOT)

GA

IN

SUPPLY VOLTAGE (V)

TPMOB0082EA

102

200 300 500 700 1000 1500

103

105

104

106

107

108

= = (A E ) = A ( ) n n

n

n+1

(n+1)

nα

nαnα nα

α

= V = K V

Vµ δ

A

11

3-4 Noise

Various types of noise may exist in a photomultiplier tubeeven when it is kept in complete darkness. These noisesadversely affect the counting accuracy, especially in caseswhere the count rate is low. The following precautions mustbe taken to minimize the noise effects.

(1) Thermionic Emission of ElectronsMaterials used for photocathodes and dynodes have lowwork functions (energy required to release electrons intovacuum), so they emit thermal electrons even at room tem-peratures. Most of the noise is caused by these thermalelectrons mainly being emitted from the photocathode andamplified by the dynodes. Therefore, cooling the photo-cathode is the most effective technique for reducing noisein applications where low noise is essential such as pho-ton counting. In addition, since thermal electrons increasein proportion to photocathode size, it is important to selectthe photocathode size as needed.Figure 17 shows temperature characteristics of dark countsmeasured with various types of photocathodes. These aretypical examples and actual characteristics vary consid-erably with photocathode size and sensitivity (especiallyred sensitivity).The head-on type Ag-O-Cs, multialkali, and GaAs photo-cathodes have high sensitivity in the near infrared, butthese photocathodes tend to emit large amounts of ther-mal electrons even at room temperatures, so usually cool-ing is necessary.

Figure 17 : Temperature Characteristics of Dark Counts

(2) Glass ScintillationWhen electrons deviating from their normal trajectoriesstrike the glass bulb of a photomultiplier tube, glass scin-tillation may occur and result in noise. Figure 18 showstypical dark current (RMS noise) versus the distance be-tween the photomultiplier tube and the metal housing caseat ground potential. This implies that glass scintillation noiseis caused by stray electrons which are attracted to theglass bulb at a higher potential. This is particularly truewhen the tube is operated with a voltage divider circuitwith the anode grounded. To minimize this problem, it isnecessary to reduce the supply voltage for the photomul-tiplier tube, use a voltage divider circuit with the cathodegrounded, or make longer the distance between the pho-tomultiplier tube and the housing. Another effective mea-sure is to coat the outer surface of the glass bulb withconductive paint which is maintained at the photocathodepotential, in order to prevent stray electrons from beingattracted to the glass bulb. In this case, however, the pho-tomultiplier tube must be covered with an insulating mate-rial since a high voltage is applied to the glass bulb. Wecall this technique "HA coating". Although Figure 18 is anexample of a side-on photomultiplier tube, similar charac-teristics will be observed for a head-on photomultiplier tube.

Figure 18 :Dark Current vs. DistanceBetween Photomultiplier Tubeand Housing Case at Ground Potential

10 7

20 400204060TEMPERATURE ( C)

DA

RK

CO

UN

TS

(s-1

)

HEAD-ON TYPEAg-O-Cs

HEAD-ON TYPEMULTIALKALI

HEAD-ON TYPEBIALKALI

GaAs

HEAD-ON TYPELOW-NOISE BIALKALI

SIDE-ON TYPELOW-NOISE BIALKALI

SIDE-ON TYPEMULTIALKALI

10 8

10 6

10 5

10 4

10 2

10 3

10 1

10 0

10 1

TPMOB0066EB

DISTANCEBETWEEN METAL CASEAND GLASS BULB

METALCASE

GLASSBULB

ANODE OUTPUT

MICROAM-METER

RMSVOLT-METER

1 M W 3 pF

- 1000 V

DARK CURRENT

RMS NOISE

10 10-8

10-9

10-10

1

0.1

RM

S N

OIS

E (

mV

)

DA

RK

CU

RR

EN

T (A

)

0 2 4 6 8 10 12DISTANCE BETWEEN METAL CASE AND GLASS BULB (mm)

TPMOC0014EC

PH

OTO

MU

LTIP

LIE

RTU

BE

12

However, in most cases, the input window of the photo-multiplier tube is exposed even with the HA coating. There-fore, in anode grounded scheme, use of good insulatingmaterial such as fluorocarbon polimers or polycarbonateis necessary around the input window in negative HV op-eration. Otherwise, a large potential difference may becreated at the input window, and could result in irregularand high dark counts.To avoid this problem, adopting a cathode groundedscheme is strongly recommended.

(3) Leakage CurrentLeakage current may be another source of noise. It mayincrease due to imperfect insulation of photomultiplier tubebase or socket pins, and also due to contamination on thecircuit board. It is therefore necessary to clean these partswith appropriate solvent like ethyl alcohol.In addition, when a photomultiplier tube is used with acooler and if high humidity is present, the photomultipliertube leads and socket are subject to frost or condensa-tion. This also results in leakage current and thereforespecial attention should be paid.

(4) Field Emission NoiseThis is voltage-dependent noise. When a photomultipliertube is operated at a high voltage near the maximum rat-ing, a strong local electric field may induce a small amountof discharge causing dark pulses. It is therefore recom-mended that the photomultiplier tube be operated at avoltage sufficiently lower than the maximum rating.

(5) External NoiseBesides the noise from the photomultiplier tube itself, thereare external noises that affect photomultiplier tube opera-tion such as inductive noise. Use of an electromagneticshield case is advisable.Vibration may also result in noisemixing into the signal.

(6) RingingIf impedance mismatching occurs in the signal output linefrom a photomultiplier tube, ringing may result, causingcount error. This problem becomes greater in circuits han-dling higher speeds. The photomultiplier tube and thepreamplifier should be connected in as short a distanceas possible, or proper impedance matching should be pro-vided at the input of the preamplifier.

3-5 Magnetic Shield

Most photomultiplier tubes are very sensitive to magneticfields and the output varies significantly even with terres-trial magnetism (approx. 0.04 mT ). Figure 19 shows typi-cal examples of how photomultiplier tubes are affected bythe presence of a magnetic field. Although photomultiplier

tubes in the photon counting mode are less sensitive tothe magnetic field than in the analog mode, photomulti-plier tubes should not be operated near any device pro-ducing a magnetic field (motor, metallic tools which aremagnetized, etc.). When a photomultiplier tube has to beoperated in a magnetic field, it is necessary to cover thephotomultiplier tube with a magnetic shield case.

Figure 19 :Typical Effects by MagneticFields Perpendicular to Tube Axis

3-6 Stability and Dark Storage

In either the photon counting mode or analog mode, thedark current and dark count of a photomultiplier tube usu-ally increase just after strong light is irradiated on the pho-tocathode. To operate a photomultiplier tube with good

Figure 20 : Effect of Dark Storage in Noise Reduction

101

0 50 100 150

102

104

103

DA

RK

CO

UN

TS

(s-1

)

TIME(min)

PHOTOMULTIPLIER TUBE LEFT IN DARKNESS

PHOTOMULTIPLIER TUBENOT LEFT IN DARKNESS

TPHOB0039JB

120

110

100

90

80

70

60

50

40

30

20

10

0-0.5 -0.4 -0.3 -0.2 -0.1 0.1 0.30.2 0.40 0 .5

TPMOB0017EB

RE

LAT

IVE

OU

TP

UT (

%)

28 mm dia.

SIDE - ON TYPE

13 mm dia.HEAD - ON TYPELINEAR - FOCUSEDTYPE DYNODES( )

38 mm dia.HEAD - ON TYPECIRCULAR CAGETYPE DYNODES( )

MAGNETIC FLUX DENSITY (mT)

13

stability, it is necessary to leave the photomultiplier tube indark state without allowing the incident light to enter thephotocathode for about one or more hours. (This is called"dark storage" or "dark adaptation".) As Figure 20 shows,dark storage is effective in reducing the dark count rapidlyin the actual measurement.

3-7 Uniformity

Uniformity is the variation in photomultiplier tube outputwith respect to the photocathode position at which lightenters. As stated in 3-2 "Collection efficiency (CE)", evenif uniform light enters the entire photocathode of a photo-multiplier tube, some electrons emitted from a certain po-sition of the photocathode are not efficiently collected bythe first dynode (Dy1). This phenomenon causes varia-tions in uniformity as shown in Figure 21. If photons entera position of poor uniformity, not all the photoelectronsemitted from there are detected, thus lowering the detec-tion efficiency. In general, head-on photomultiplier tubesprovide better spatial uniformity than side-on photomulti-plier tubes. For either type, good uniformity is obtainedwhen light enters around the center of a photocathode.

Figure 21 : Typical Uniformity

3-8 Signal-to-Noise Ratio

This section describes theoretical analysis of the signal-to-noise consideration in both photon counting and ana-log modes. The noise being discussed here is mainly shotnoise superimposed on the signal.(1) Analog ModeWhen signal light enters the photocathode of a photomul-tiplier tube, photoelectrons are emitted. This process oc-curs accompanied by statistical fluctuations. The photo-cathode signal current or average photocurrent Iph there-fore includes an AC component which is equal to the shotnoise iph expressed below.

where e is the electron charge and B is the bandwidth ofthe measurement system.The shot noise which is superimposed on the signal canbe categorized by origin as follows :

a) Shot Noise Resulting from Signal LightSince the secondary electron emission in a photomul-tiplier tube occurs with statistical probability, the result-ing output also has statistical fluctuation. Thus the noisecurrent at anode, isa, is given by

where µ is the gain of the photomultiplier tube, F is thenoise figure of the photomultiplier tube. If we let thesecondary electron emission ratio per dynode stagebe δn, the noise figure for the photomultiplier tube hav-ing n dynode stages can be expressed as follows:

Supposing that δ 1=5, δ 2= δ 3= ……… = δ n=3, the noisefigure takes a value of approximately 1.3 .At this point, the photocurrent Iph is given by

where Pi is the average light level entering the photo-multiplier tube, η ( λ ) is the photocathode QE at thewavelength λ , α is the photoelectron CE and h is theenergy per photon.

b) Shot Noise Resulting from BackgroundAs with the shot noise caused by signal light, the shotnoise at the anode resulting from the background Pb

can be expressed as follows:

where Ib is the equivalent average cathode current pro-duced by the background light.

c) Shot Noise Resulting from Dark CurrentDark current may be categorized by cause as follows:

Thermionic emission from the photocathode anddynodes.Fluctuation by leakage current between electrodes.Field emission current and ionization current fromresidual gases inside the tube.

Among these, a major cause of the dark current is ther-mionic emission from the photocathode.

isa = 2eIphFB µ

F=1

1 1(1+ + + + )1 2

1 1 nδδ δ δ δ

• • • • • • • • • • •• • • • • ••

Iph=P i ( ) e

hη λ α

iba = 2eIbFB

Ib =P b ( ) e

h

µη λ α

iph= 2eIphB

(1) Head-on Type (2) Side-on Type

100

50

0AN

OD

E S

EN

SIT

IVIT

Y (%

)

PHOTOCATHODEVIEWEDFROM TOP

SE

NS

ITIV

ITY

(%)

AN

OD

E

50SENSITIVITY(%)

ANODE

PHOTOCATHODE

GUIDE KEY

500 1000

100

TPMHC0085EB TPMSC0030EB

14

In a low bandwidth region up to several kHz, the NEPmainly depends on the shot noise caused by dark cur-rent (the latter component in the above equation). In ahigh bandwidth region, the noise component (the formercomponent in the above equation) resulting from thecathode radiant sensitivity (Sp/m in the equation) pre-dominates the NEP.The noise can also be defined as equivalent noise in-put (ENI). The ENI is basically the same parameter asthe NEP, and is expressed in lumens (Sp is measuredin units of amperes per lumen in this case) or watts.

(2) Photon Counting ModeIn the analog mode, all pulse height fluctuations occurringduring the multiplication process appear on the output.However, the photon counting mode can reduce such fluc-tuations by setting a discrimination level on the output pulseheight, allowing a significant improvement in the signal-to-noise ratio.In the photon counting mode in which randomly gener-ated photons are detected, the number of signal pulsescounted for a certain period of time exhibits a temporalfluctuation that can be expressed as a Poisson distribu-tion. If we let the average number of signal pulses be N, itincludes fluctuation (mean deviation) which is expressedin the shot noise n = N. The amplifier noise can be ig-nored in the photon counting mode by setting the photo-multiplier tube gain at a sufficiently high level, so that thediscrimination level can be easily set higher than amplifiernoise level.As with the analog mode, dark current may be grouped bycause as follows:(a)Shot noise resulting from signal light

nph = Nph

(Nph is the number of counts by signal light)

(b) Shot noise resulting from background lightnb = Nb

(Nb is the number of counts by background light)

(c) Shot noise resulting from dark countsnd = Nd

(Nd is the number of dark counts)

In actual measurement, it is not possible to detect Nph sepa-rately. Therefore, the total number of counts (Nph+Nb+Nd)is first obtained and then the background and dark counts(Nb+Nd) are measured over the same period of time by

Therefore the shot noise resulting from anode dark cur-rent ida can be expressed as shown below:

where Id is the equivalent average dark current fromthe photocathode.

d) Noise from Succeeding AmplifierWhen an amplifier with noise figure Fa is connected tothe photomultiplier tube load, the noise converted intothe input of the amplifier is given by

where Req is the equivalent resistance used to connectthe photomultiplier tube with the amplifier, T is the ab-solute temperature and k is the Boltzmann constant.

e) Signal-to-Noise RatioTaking into account the background noise (Ib+Id), thesignal-to-noise ratio (S/N) of the photomultiplier tubeoutput becomes

... (1)

Among the above equations, the amplifier noise canbe generally ignored because the gain m of the photo-multiplier tube is sufficiently large, so the signal-to-noiseratio can be expressed as follows:

................. (1)'

f) Noise Equivalent PowerIn addition, the noise can also be expressed in termsof noise equivalent power (NEP). The NEP is the lightlevel required to obtain a signal-to-noise ratio of 1, thatis, the light level to produce a signal current equivalentto the noise current. The NEP indicates the lower limitof light detection and is usually expressed in watts.From equation (1)' above, the NEP at a given wave-length can be calculated by using Ib = 0 and S/N=1, asfollows:

S/N = =2eF(Ipha+2Ida) B 2eF(SpP i+2Ida) B

I pha Sp P i

where Ipha is anode signal current, Ida is anode dark current,and Ipha=Iph =Sp P iSp: anode radiant sensitivity, P i : input power

Then calculate the variable P i

S pP i = 2eF (SpPi+2Ida) B

(SpP i )2 - 2eF (S pP i+2I da) B = 0

m

m

m

m

m

Therefore, NEP is given by P i as follows:

P i = +eF B (eF B )2+4eFIda B

S p S p

m m mida = 2eIdFB m

4FakTBReq

Iamp =

Iph

2eFB Iph+2(Ib+Id) +(4FakTB/Req)/ 2S/N =

Iph

2eFB Iph+2(Ib+Id)S/N

15

removing the input light. Then Nph is calculated by sub-tracting (Nb+Nd) from (Nph+Nb+Nd). From this, each noisecomponent can be regarded as an independent factor, sothe total noise component can be analyzed as follows:Here, substituting nph = Nph, nb = Nb and nd = Nd

Thus the signal-to-noise ratio (S/N) becomes

.............. (3)

The number of counts per second for N'ph, N'b and N'd iseasily obtained as shown below, respectively. t is the mea-surement time in seconds.

N'ph=Nph/t, N'b=Nb/t, and N'd=Nd/tAccordingly, the equation (3) can be expressed as follows:

............ (3)'

This means that the signal-to-noise ratio can be improvedas the measurement time is made longer.

By replacing the measurement time and the number ofcounts per second with the corresponding frequency andcurrent, with t=1/(2B) and N'x=Ix/e (e= 1.6 × 10-19 C) re-spectively, it becomes clear that equation (1)' is equiva-lent to equation (3)' except for the noise figure term.

In photon counting mode, if we define the detection limitas the light level where the signal-to-noise ratio equals to1, the number of signal count per second N'ph at the de-tection limit can be approximated below, from equation(3)' under the condition that the measurement time is onesecond and the background light can be disregarded.

............. (4)

At this point, if the dark count N 'd is more than severalcounts per second, the detection limit can be approximatedwith an error of less than around 30 %.

If we let the QE at a wavelength λ (nm) be η ( λ ), the

N'ph s-12N' d

N'ph t

N'ph+2(N' b+N' d)S/N =

100

101

102

103

104

105

106

107

108

109

1010

10-18

10-19

10-17

10-16

10-15

10-14

10-13

10-12

10-11

10-10

10-9

10-8

PHOTON NUMBER ( S-1 mm-2 )

3.6 × LIGHT POWER ( W mm-2 ) at 550 nm

incident light power Po at the detection limit can be ap-proximated as follows:

.................(5)

For your reference, let us calculate the power (P) of a pho-ton per second as follows:

As an example, the table below shows the relation be-tween the light power and the number of photons at awavelength of 550 nm.

In contrast to the signal pulse height distribution (PHD)similar to a Poisson distribution, the dark current pulsesare distributed on the lower pulse height side. This is be-cause the dark current includes thermal electrons not onlyfrom the photocathode but also from dynodes. Therefore,some dark current component can be effectively eliminatedby setting a proper discrimination level without reducingmuch of the signal component. Furthermore, by placingan upper discrimination level, the photon counting modecan also eliminate the influence of environmental radia-tion which produces higher noise pulses and often causesignificant problems in the analog mode. It is now obviousthat the photon counting mode allows the measurementwith a higher signal-to-noise ratio than in the analog mode,which is even greater contribution than that obtained fromthe noise figure F.

Constant

Electron Charge

Speed of Light in Vacuum

Planck's Constant

Boltzmann's Constant

1 eV Energy

Wavelength in VacuumCorresponding to 1 eV

ReferencePhysical Constants

Symbol

e

c

h

k

eV

–

Value

1.602 × 10-19

2.998 × 108

6.626 × 10-34

1.381 × 10-23

1.602 × 10-19

1240

Unit

C

m/s

J.s

J/K

J

nm

Photon Number and Light Power

W-16

× ( )

2.8×10 ×Po

N'dη λλ

W-16

2×10

hcP=λ

λ

NphNph

n tot Nph+2(Nb+Nd)S/N= =

Nph+2(Nb+Nd)n tot =

16

4. Measurement SystemsPhoton counting can be performed with several measure-ment systems, including simple sequential measurementsand sampling measurements depending on the informa-tion to obtain or the light level and signal timing condi-tions.

4-1 Synchronous Photon CountingUsing Chopper

Using a mechanical chopper to interrupt incident light, thismethod makes light measurements in synchronization withthe chopper operation. More specifically, signal pulses andnoise pulses are both counted during the time that lightenters a photomultiplier tube, while noise pulses arecounted during light interruption for subtracting them fromsignal pulses and noise pulses. This method is effectivewhen a number of noise pulses are present or when ex-tremely low level light is measured. However, since thismethod uses a mechanical chopper, it is not suitable forthe measurement of high-speed phenomena. This methodis also known as the digital lock-in mode. Figure 22 showsa block diagram for this measurement system, along withthe timing chart.Figure 22 : Synchronous Photon Counting

Using Chopper

4-2 Time-Resolved PhotonCounting by Repetitive Sampling

This method uses a pulsed light source to measure tem-poral changes of repetitive events.Each event is measured by sampling at a gate timing

INCIDENTLIGHT

LED

CHOPPER

PHOTO TRANSISTOR

PMT AMP

DISCRIMINATOR

GATECIRCUIT COUNTER

SYNCHRONOUSSIGNAL

CHOPPER WIDTH

CHOPPEROPERATION

GATE CIRCUITOPERATION

SETTLING TIME

GATE FOR SIGNAL

GATE FOR NOISE

a

b

c

d

TPHOC0030EA

SAMPLING TIME

slightly delayed from the repetitive trigger signals. The sig-nal measured at each gate is accumulated to reproducethe signal waveform. This method is sometimes called thedigital boxcar mode and is useful for the measurement ofhigh-speed repetitive events. Figure 23 shows the timechart of this method.Figure 23 : Time-Resolved Photon Counting

by Repetitive Sampling

4-3 Time-Resolved Photon Countingby Multiple Gates

This method sequentially opens multiple gates and mea-sures the light level in a very short duration of the opengate, allowing a wide range of measurement from slowevents to fast events. This method can also measure singleevents and random events by continuously storing datainto memory. The time chart for this method is shown inFigure 24.Figure 24 : Time-Resolved Photon Counting

by Multiple Gates

TRIGGERSIGNAL

CLOCKSIGNAL

SIGNAL LIGHT

ADDER CIRCUITGATE SIGNAL

SUBTRACTER CIRCUITGATE SIGNAL

ADDITION GATE

SUBTRACTIONGATE

a

b

c

d

e

f

g

TIME

A1

B2C3

ZnYn

A1 An

B1C1

BnCn

YnZnZ2Z1

T1 T2 Tn

A2

B2C2

SITPHOC0031EB

CO

UN

TS

INCIDENTLIGHT

GATE 1

ON

OFF

GATE 2

ON

OFF

COUNT DATA

TPHOC0032EBTIME

17

4-4 Time-Correlated PhotonCounting

Time-correlated photon counting (TCPC) is used in con-junction with a high-speed photomultiplier tube for fluo-rescence lifetime measurement (in picoseconds to nano-seconds). By making the count rate sufficiently small rela-tive to repetitive excitation light from a pulsed light source,this method measures time differences with respect to in-dividual trigger pulses synchronized with excitation sig-nals in the single photoelectron state.Actual fluorescence and emission can be reproduced withgood correlation by integrating the signals. Since thismethod only measures the time difference, it provides abetter time resolution than the pulse width obtainable froma photomultiplier tube. A typical system for the TCPC con-sists of a high-speed preamplifier, a discriminator with less

Figure 25 :TCPC System

time jitter called a constant fraction discriminator (CFD), atime-to-amplitude converter (TAC), a multichannel pulseheight analyzer (MCA) and a memory or computer. Figure25 shows the block diagram, time chart for this measure-ment system and one example data for fluorescence de-cay time.Besides TCPC, time-resolved measurement also includesphase difference detection using the modulation method.This method is sometimes selected due to advantagessuch as a compact light source and simpler operating cir-cuits.

Reference: "TECHNICAL INFORMATION Applicationof MCP-PMTs to time-correlated single photon countingand related procedures" (available from Hamamatsu).

"TECHNICAL INFORMATION Modulated Photomulti-plier Tube module H6573" (available from Hamamatsu)

PULSE LIGHT SOURCE FILTERSAMPLE

PINPHOTODIODE

PMT AMP.

(b)

(c)

(a)

(d)

DISCRIMINATOR

DISCRIMINATOR

CFD

TAC MCA

TRIGGER

COMPUTER

DELAY CIRCUIT

(A) Measurement block diagram

(B) Time chart

(C) Example of TCPC Measurement (Sample : Cryptocyanine in ethanol)

TRRIGER

PMT OUTPUT

CFD OUTPUT

TAC OUTPUT

t 1

v1

t 3

v3

t 2

v2

TPHOC0033ED

FILTER

TIME (ns)0.20 0.4 0.6 0.8 1.0

CO

UN

TS

(s-1

)

104

103

102

101

100

FLUORESCENCE DECAY

(a)

(b)

(c)

(d)

18

(5) Dark Count → Lower Detection LimitThe dark count is an important factor for determining thelower detection limit of a photomultiplier tube. Selectingthe photomultiplier tube with minimum dark counts is pre-ferred. In general, for the same electrode structure, thedark count tends to increase with a larger photocathodeand higher sensitivity in a long wavelength range. When aphotomultiplier tube is used in a long wavelength rangeabove 700 nm, cooling the photomultiplier tube is recom-mended.

(6) Response Time → Maximum Count Rate,Time Resolution

The maximum count rate (s-1) in the photon counting modeis determined by the time response of the photomultipliertube and the frequency characteristics of the signal pro-cessing circuit, or by the pulse width.Most photomultiplier tubes have no problem with the timeresponse up to a maximum count rate (random pulse) of3×106 s-1. However, in applications where the maximumcount rate higher than this level is expected, a photomul-tiplier tube with the rise time (t r) shorter than 5 ns must beselected. In time-correlated photon counting (TCPC), theelectron transit time spread (TTS) is more important thanthe rise time itself.

5-2 Photomultiplier Tubes forPhoton Counting

Table 1 (on pages 28 and 29) is a listing of typicalHamamatsu photomultiplier tubes designed or selectedfor photon counting, showing general specifications for thespectral response and configurations. For more informa-tion, refer to the Hamamatsu photomultiplier tubes cata-log. In addition to photomultiplier tubes listed in Table 1,you can choose from Hamamatsu photomultiplier tubesfor photon counting. Please consult our sales office.

5-3 Related Products

There are many related products used in photon count-ing. The following sections introduce major products forphoton counting available from Hamamatsu: preamplifi-ers, photon counting units, photon counting heads, pho-ton counting boards, high-voltage power supplies, cool-ers and housings. For further details, refer to individualcatalogs.

5. Selection GuideThis section describes how to select the optimum photo-multiplier tube for photon counting, along with their briefspecifications and related products. The following notesshould be taken into account in selecting the photomulti-plier tube that matches your needs.

5-1 Selecting The PhotomultiplierTube

(1) Photomultiplier Tube StructurePhotomultiplier tubes are roughly grouped into side-on andhead-on types, so it is important to select the photomulti-plier tube structure type according to the optical measure-ment conditions.Side-on photomultiplier tubes have a rectangular photo-sensitive area and are therefore suitable for use in spec-trophotometers where the output light is in the form of aslit, or for the detection of condensed light or collimatedlight.Head-on photomultiplier tubes offer a wide choice of pho-tosensitive areas from 8 mm to 120 mm in diameter andcan be used under various optical conditions. Note, how-ever, that selecting the photomultiplier tube with a photo-sensitive area larger than necessary may increase darkcounts, thus deteriorating the signal-to-noise ratio.

(2) Photocathode Quantum Efficiency (QE)The QE has direct effects on the detection efficiency. It isimportant to select a photomultiplier tube that provides highQE in the desired wavelength range.

(3) GainGain required of the photomultiplier tube differs depend-ing on the gain or equivalent noise input of the amplifierconnected. As a general guide, it is advisable to select aphotomultiplier tube having a gain higher than 1 × 106,although it depends on the pulse width of the photomulti-plier tube.

(4) Single Photoelectron Pulse Height Distribution(PHD)

Although not listed in the catalog, the PHD is an importantfactor since it relates to photomultiplier tube detection ef-ficiency and stability. Hamamatsu designs photomultipliertubes for photon counting, while taking the PHD into ac-count. As a guide for estimating whether PHD is good ornot, the peak to valley count ratio is sometimes used. (SeeFigure 6.)

19

Notes : An IBM PC/AT compatible personal computer with WindowsTM Me/98SE/98/95 and equipped with an ISA bus is required for M7824 and M8503. A D-type socket assembly is required for the operation of a photomultiplier tube.

Related Products for Photon Counting

H6180 SERIESH7360 SERIESH6240 SERIESH7155 SERIESH7421 SERIES POWER SUPPLY

(LOW VOLTAGE)

PERSONALCOMPUTER

H3460 SERIES C3589

C3830OR

C4720

PHOTON COUNTING UNIT

POWER SUPPLY(HIGH/LOW VOLTAGES)

PHOTON COUNTINGHEAD

PHOTON COUNTINGHEAD PRESCALER

TPHOC0029EB

< Configuration Examples>

C4720

POWER SUPPLY(HIGH/LOW VOLTAGES)

COUNTER

PERSONALCOMPUTER

PERSONALCOMPUTER

PHOTO-MULTIPLIER

TUBEC3866C6465

D-TYPESOCKETASSEMBLY

PERSONALCOMPUTERH7467

RS-232C INTERFACE

POWER SUPPLY(LOW VOLTAGE)

PHOTON COUNTING BOARD

COUNTER

PHOTON COUNTING BOARD

COUNTER

PHOTON COUNTING BOARD

PHOTON COUNTINGHEAD

: Available from Hamamatsu

HV

HV LV

LV

M7824M8503

M7824M8503

M7824M8503

R

Photon Counting Heads<H7360-01, H6180-01, H6240 series>These photon counting heads consist of a photomultiplier tube, a voltage divider, an amplifier, a discriminator and a high-voltage power supply, all included in a compact metallic case. The H7360-01, H6180-01 and H6240 series just require +5 V.All of these photon counting heads output TTL compatible signals for easy connection with pulse counters. Since thephotomultiplier tube supply voltage and discrimination voltage are preset at the optimal levels, there is no need foradjustment before use. For the H7360-01 and H6180-01, the E6264 mount flange is optionally provided for connection toother equipment.

SPECIFICATIONSH7360-01 H6180-01 H6240 H6240-01 H6240-02 Unit

300 to 650 300 to 650 185 to 680 185 to 850 185 to 900 nmφ 21 φ 15 4 x 20 4 x 6 mm

6×106 6×106 2.5×106 s-1

15 10 30 80 400 s-1

Positive Logic : 3 V, 9 ns Positive Logic : 3 V, 9 ns Positive Logic TTL 30 ns —

+5 V (125 mA) +5 V (125 mA) +5 V (80 mA) —

ParameterSensitive Spectral Range

Minimum Effective AreaCounting Linearity A

(Random Pulse)

Dark Count at +25 C [Typ.]

Output PulseInput Voltage (Current)

NOTE: A At –10 % deviation from linear output.

<H7155 series>H7155 series are compact photon counting heads comprising a metal package PMT, high-speed photon countingcircuit, and high voltage power supply. The operation requires only connecting to a +5 V power supply and a pulsecounter. There is no need for discrimination level or high voltage adjustment by users.H7155 series accept direct light input or an optical fiber input. The fiber adaptor E5776 is optionally available.The H7155-20 (300 nm to 650 nm) and -21 (300 nm to 850 nm) have a 1/4 prescaler to deliver a linear count rate of1×107 s-1.

SPECIFICATIONS

20

φ 81.5×106

Positive Logic TTL: 30 ns

+5 V ( 50 mA Max.)

22 x 50 x 50

300 to 650 300 to 850

100 600

Sensitive Spectral RangeMinimum Effective AreaCounting Linearity (Random Pulse) A

Dark Count at +25 C [Typ.]

Output Pulse WidthInput Voltage (Current)Dimensions (W x H x D)

NOTE: A At –10 % deviation from linear output.

Parameter H7155 H7155-01 Unitnmmm

s-1

s-1

—

—

mm

SPECIFICATIONS Parameter

Sensitive Spectral RangeMinimum Effective AreaDark Count at +25 C [Typ.]

Counting LinearitySerial InterfaceIntegration TimeInput Voltage (Current)

H7467 H7467-01 Unit300 to 650 300 to 850 nm

φ 8 mm

1.5×106 s-1

100 600 s-1

NOTES: At -10 % deviation rom linear output (random pulse.) The Serial Interface requires the following communication specifications:9600 baud, No parity, 8 data bits, 1 stop bit.

<H7467 series>The H7467 series is a compact photon counting head with the intelligence of a microcontroller. Since the detectorinterfaces diretly to a personal computer, the opeation only requires connecting to a +5 V power supply: no need fordiscrimination level or high voltage adjustment by users.

AB

RS-232 10 to 10 000 (10 steps) ms

+5V (180 mA)

A

B

Parameter H3460-53 H3460-54 Unit

Sensitive Spectral Range

Minimum Effective Area

Counting Linearity

M7425Dark Count

C8137

Output Pulse Width

Main Unit Input Voltage Range

Main Unit Input Current

at 1.5 × 106 s-1 output

<H3460 series>The H3460 series photon counting heads incorporate a photomultiplier tube and a high-speed amplifier/discriminator into acompact metallic case. By connecting to an external high-voltage power supply for the photomultiplier tube and a low-voltagepower supply for the amplifier/discriminator, photon counting can easily be performed.Hamamatsu also offers the C3589 prescaler that divides the count rate by 10 for use with the H3460-53 and -54,allowing measurement over a wide dynamic range without using a high-speed counter.

NOTE: At –10 % deviation from linear output.

SPECIFICATIONS

20 40

Sensitive Spectral Range

Minimum Effective AreaCounting Linearity (Random Pulse) Dark Count at +25 °C [Typ.]Output Pulse Width

Recommened High Voltage (Current)for Photomultiplier Tube

Input Voltages (Current)for Preamplifier and Discriminator

nm

mm

s-1

s-1

—

—

—

300 to 650

φ 21

1.3×107

ECL Balanced Line: 3 ns

Approx. +1000 V ( 230 µA)

+5 V ( 35 mA),–5 V ( 150 mA )

<H7421 series>The H7421 series is a compact photon counting head consisting of a metal package PMT with a cooler, a high speedphoton counting circuit and a high voltage power supply. The H7421-40 utilizes a GaAsP semiconductor photocathodewhich detects single photons from 300 nm to 720 nm in wavelength. The H7421-50 utilizes a GaAs semiconductorphotocathode which detects single photons from 380 nm to 890 nm in wavelength. Both types have higher quantumefficiency compared to the conventional alkali metal photocathode at their peak wavelenghs.By using a temperature monitor output from the thermistor, the operating temperature of the H7421 series can bemonitored.The output TTL signal can be handled easily by simply connecting to a counter.To obtain good performance, the H7421 should be kept between +5 °C to +35 °C in operation.

SPECIFICATIONS

300 to 720 380 to 890 nm

φ 5 mm

1.5×106 s-1

40 50 s-1

100 125 s-1

Positive Logic TTL: 30 ns —

+5 V

50 mA

Parameter H7421-40 H7421-50 Unit

COOLING CHARACTERISTICSParameter H7421-40 H7421-50 Unit

Cooling Method Thermoelectric effect —

Cooling Temperature (MAX.∆T *) 35 °CCooling Time Approx. 5 min

Peltier Cooler Input Current 2.0 A

21

A

A

[Typ.]

NOTES: Operating with M7425(power supply unit) and A7423 (heatsink with fan) Operating with C8137 (temperature control and power supply unit: T=0 °C ) and A7423 After 30 min storage in darkness At -10 % deviation from linear output (random pulse) ∗∆T means temperature difference from an ambience.

A

BC

A

A

A

A C

CB

<C3866 C6465>The C3866 photon counting unit converts photomultiplier tube output pulses into a 5 V digital signal by using a built-inamplifier/discriminator. Photon counting with high signal to noise ratio can be easily performed by connecting anexternal pulse counter to the output of the C3866 and supplying a low voltage. The high-speed electronic circuit usedin the C3866 ensures high-precision photometry with high linearity up to 107 s-1. Due to the built-in prescaler (divisionby 10), the C3866 does not require a high-speed pulse counter.The C6465 offers high output linearity up to 106 s-1 and an output pulse width of 30 ns, allowing use with a general-purpose pulse counter.

Parameter

Photon Counting Unit

SPECIFICATIONS

Input Impedance

Discrimination Level (input equivalent)

Prescaler

Maximum Count Rate (Random Pulse: –10 % deviation)

Pulse Pair Resolution

Output Pulse

Output Pulse Width

Input Voltage ( Current )

Dimensions (W × H × D)

C3866 C6465

50 Ω

–0.5 mV to –16 mV

÷1, ÷10

(÷1) 4×106 s-1, (÷10) 1×107 s-1

(÷1) 25 ns, (÷10) 10 ns

CMOS 5 V

(÷1) 10 ns, (÷10) Depends on Count Rate

+5.2 V ( 150 mA), –5.2 V ( 300 mA)

88 mm× 32 mm× 170 mm

22

50 Ω–2.2 mV to –31 mV

–

1×106 s-1

60 ns

Positive TTL

30 ns

+5 V (60 mA), –5 V (120 mA)

60 mm × 43.2 mm × 105 mm

Signal Input Level TTL positive logic

Input Signal Pulse Width 10 ns or more

Input Impedance 50 ΩMaximum Count Frequency 50 MHz

CounterMaximum Count per Gate 232 counts

Internal Gate Time 50 µs to 10 sGate

External Gate Time 100 ns or more

Trigger Method Software, external trigger inputTrigger

External Trigger TTL negative logic

General-Purpose Input Signal TTL negative logic/ 8 bits

Output Output Signal Open collector/ 8 bits

OS WindowsTM Me/98SE/98/95

Bus ISA bus

Address Space Selectable with DIP switch on board

Input Voltage (Current) 5 V (1A)

Dimension ISA board half size

NOTES: Contact Hamamatsu for using other interfaces.

This input voltage(current) is supplied through the ISA bus.

Parameter

<M7824>The photon counting board M7824 is designed for direct plug-in to the ISA bus slot in a PC(WindowsTM Me/98SE/98/95).Photoelectoron pulses converted into logic (TTL) signals are counted by M7824 and sent to a PC. A gate functionis also included to make photon counting easier over a wide dynamic range.M7824 applies a dual count method that allows time-resolved photon counting of high-speed optical phenomena withno dead time between gates. Simultaneous 2-channel measurements are also possible by using two M7824 boards.

Photon Counting Board

Value

SPECIFICATIONS

A

B

A

B

Input Voltage

Input Current [Typ.]

Output Voltage Range

Maximum Output Current

Line Regulation [Typ.]

Load Regulation [Typ.]

Against 0 % to 100 % Load Change

Ripple Noise (p-p) [Typ.]

Dimensions (W × H × D)

Value

High Voltage Power Supplies

Parameter

<M8503>The photon counting board M8503 is designed for direct plug-in to the ISA bus slot in a PC (WindowsTM Me/98SE/98/95).Photoelectron pulses converted into logic (TTL) signals are counted by the M8503 and sent to a PC. A gate function isincluded to make photon counting easier over a wide dynamic range.The M8503 uses a dual count method that allows time-resolved photon counting of high-fast optical phenomena with nodead time between gates.The gate time can be set as short as 50, 100 or 200 ns making the M8503 ideal for time-resolved photon counting of ultra-fast optical phenomena. An 8000 gate memory allows continuous measurements for up to 1.6 ms. The M8503 also has abuilt-in integration circuit for enhancing signal quality.The M8503 delivers flexible, cost-effective high performance photon counting over a wide dynamic range.

Photon Counting Board

SPECIFICATIONS

23

15

C4900 C4900-01 C4900-50 C4900-51

+12±0.5 +15±1 +12±0.5

14 14 15

90 95 90 95

0.6 0.5 0.5

0 to –1250

0.6

0 to +1250

+15±1

Parameter

<C4900 series (on-board type)>Aiming at compactness, low cost yet high performance, the C4900 series is a modular high-voltage power supplythat can be directly mounted on a PC board. The newly designed circuitry ensures both high performance and lowpower consumption. Enhanced protective functions are also included as standard features.

NOTES : At maximum output voltage. At maximum output voltage and current.

C4900, -50 : +15 V ±1 V / C4900-01, -51 : +12.0 V ±0.5 V

SPECIFICATIONSUnit

with no load

with full load

±0.01

±0.01

0.007

46 × 24 × 12

V

mA

mA

V

mA

%

%

%

mm

A

B

A

B

A

C

A B

C

Signal Input channel 2 channelSignal Input Level TTL positive logicInputSignal Pulse Width 10 ns or moreInput Impedance 50 ΩMaximum Count Frequency 50 MHz

CounterMaximum Count per Gate 224 counts

Gate Internal Gate Time 50 ns, 100 ns, 200 nsTrigger Method external trigger input

TriggerExternal Trigger TTL negative logic Gate time : 50ns 150 ns or moreDelay Time Gate time : 100ns 300 ns or more Gate time : 200ns 600 ns or more

Integration Times 16 777 215Memory 8000 gate data (at 1ch input)OS WindowsTM Me/98SE/98/95Bus ISA busAddress Space Selectable with DIP switch on boardInput Voltage(Current) + 5 V (1.5A)Dimension ISA board full sizeNOTE: Contact Hamamatsu for using other interfaces. This input voltage(current) is supplied through the ISA bus.A B

A

B

Input Voltage

Input Current [Typ.]

Output Voltage Range

Maximum Output Current

Line Regulation [Typ.]

Against ±1 V Input Change

Load Regulation [Typ.]

Against 0 % to 100 % Load Change

Ripple Noise (p-p) [Typ.]

Dimensions (W × H × D)

C4710-52C4710-02Parameter

<C4710 series (on-board type)>The C4710 series is an on-board type high-voltage power supply designed for photomultiplier tube operation.It combines high performance with ease of use.

NOTES : At maximum output voltage.

At maximum output voltage and current.

SPECIFICATIONSC4710 C4710-01 C4710-50 C4710-51 Unit

with no load

with full load

+15±1 +12±1 +15±1 +12±1

95 120

340

95 120

1

+24±1

65

+24±1

±0.01 ±0.015 ±0.02 ±0.02±0.015 ±0.015

±0.01 ±0.015 ±0.01 ±0.01±0.01 ±0.01

65

260 260 340145 145

–240 to –1500

V

mA

mA

V

mA

%

%

%

mm

0.005

65 × 27.5 × 45

+240 to +1500

24

A

B

A

B

AB

AC Input Voltage

Load Regulation [Typ.]Against 0 % to 100 % Load Change

Maximum Output CurrentLine Regulation [Typ.]Against ±10 % Line Voltage Change

Output Voltages

High Voltage PowerSupply SectionParameter

<C3830, C4720 (bench-top type)>The C3830 and C4720 are multipurpose power supplies that provide a high voltage output for photomultiplier tube operationand low voltage outputs (±5 V, ±15 V) for peripheral devices such as the Hamamatsu preamplifier and photon counting unit.

SPECIFICATIONS

NOTES : At maximum output voltage.

At maximum output voltage and current.

Unit

–200 to –1500(Variable)

+200 to +1500(Variable)

±15(±0.75)(Fixed)

±5V PowerSupply Section

±15V PowerSupply Section

V

±0.005

±0.01

0.005

1

±0.005

±0.5

0.16

500

±0.015

±0.5

0.06

200

%

%

%

mA

100/120/230 V (50 Hz/60 Hz)100/115/220 V (50 Hz/60 Hz) —

C3830C4720

Ripple Noise (p-p) [Typ.]

A

B

A

B

AB

C3830 C4720±5(±0.25)

(Fixed)

Output Voltage

Maximum Output Current

Line Regulation [Max.] Against ±10 % Line Voltage

Load Regulation [Max.] Against 0 to 100 % Load Change

Ripple Noise (p-p) [Max.]

AC Input Voltage

Parameter

<C3350 (bench-top type)>The C3350 is a bench-top high-voltage power supply designed for general-purpose photomultiplier tube applications.

SPECIFICATIONS

NOTES : At maximum output voltage.

Value

Output Voltage

Maximum Output Current

Line Regulation [Max.] Against ±10 % Line Voltage Change

Load Regulation [Max.] Against 0 % to 100 % Load Change

Ripple Noise (p-p) [Max.]

AC Input Voltage

0 V to ±3000 V

10 mA

± (0.005 %+10 mV)

±(0.01 %+50 mV)

0.0007 %

100/115/220/230 V (50 Hz/60 Hz)

A

B

A

B

AB

25

Parameter

<C3360 (bench-top type)>The C3360 is a bench-top high-voltage power supply specifically designed for the MCP-PMT operation.

SPECIFICATIONS

NOTES : At maximum output voltage.

,At maximum output voltage and current.

Value

0 V to –5000 V

1 mA

± (0.001 %+0.05 V)

± (0.001 %+0.05 V)

0.0004 %

85 V to 132 V / 170 V to 264 V

A

B

A

B

AB

Parameter

<C4877 series, C4878 series>In addition to high cooling capability, the C4877 series and C4878 series thermoelectric coolers are constructedwith enhanced electrostatic and magnetic shielding. This minimizes the influence of external noise on thephotomultiplier tube and thus significantly improves photometric accuracy. These coolers offer user-friendlyfunctions such as easy temperature control and pilot lamp blanking.The C4877 series is designed for use with 38 mm (1-1/2") or 51 mm (2 ") diameter head-on photomultiplier tubesand can be used with the E2762 series socket assembly or the C2759 series socket assembly with a built-inpreamplifier ideal for photon counting. The C4878 series coolers are specifically designed for MCP-PMTs. (TheE3059-500 holder is available.)

Coolers

SPECIFICATIONSDescription / Value

Cooling

Heat Exchange Medium

Water Flow Rate

Temperature Controllable Range (with cooling water at +20 °C)

AC Input Voltage

Thermoelectric Effect

Water

1 L/min to 3 L/min

–30 °C to 0 °C

100/120/230 V (50 /60 Hz)

At maximum output voltage and current.

Cooling Temperature

Water Flow Rate

AC Input Voltage

Parameter

<C659 series>The C659 series is a water-cooled thermoelectric cooler that reduces photomultiplier tube temperature to –20 °C(C659-50) or –15 °C (C659-70). The C659-50 is designed for 28 mm (1-1/8 ") and 38 mm (1-1/2 ") diameter head-onphotomultiplier tubes. The C659-70 is specifically intended for use with 28 mm (1-1/8 ") diameter side-onphotomultiplier tubes. The E1135 series D-type socket assemblies are also provided for exclusive use with the C659series coolers.

SPECIFICATIONSC659-50 series

Cooling Thermoelectric Effect

Heat Exchange Medium Water

1 L/min to 3 L/min

Approx. –20 °C

115/220V (50/60Hz)

C659-70 series

Approx. –15 °C

Cooling water : +20 °C, Cooling temperature may differ depending on the photomultiplier tube type.

A

A

26

<E1341 series>The E1341-01 is a metal housing designed for 51 mm(2") diameter head-on photomultiplier tubes operated at roomtemperature. The E5859 series D-type socket assembly is also available, which can be housed in the E1341-01 along with aPMT. The E1341-01 ensures complete light-shielding and also accommodates a magnetic shield case(E989-62 soldseparately).The E1341-01 housing can be easily attached to a monochromator by preparing a simple adapter.The Copal No.3shutter can be directly attached to the E1341-01.

Housing

<C5594 series>The C5594 series is a wide-band amplifier with a high gain. The frequency cut-off is as high as 1.5 GHz,enabling amplification of high-speed output pulses from all types of photomultiplier tubes with good fidelity. Inparticular, the C5594 series is ideally suited for fluorescence lifetime measurement in single photon level using anMCP-PMT and other timing property measurements using high-speed photomultiplier tubes. The input/outputconnectors are available in either BNC or SMA configuration. For more details, refer to the individual data sheet.

High-Speed Amplifier

Parameter

SPECIFICATIONSValue

Input Voltage

Maximum Input Signal Power

Frequency Bandwidth (–3 dB)

Gain

Input / Output Impedance

Current Consumption

+12 V to +16 V

10 mW

50 kHz to 1.5 GHz

36 dB (63 Times)

50 Ω

95 mA

Hamamatsu provides D-type socket assemblies using a voltage divider circuit tailored for photon counting.A variety of types are available for use with different size photomultiplier tubes.

13mm (1/2 ") diameter side-on tubes ........... E850-2228mm (1-1/8 ") diameter side-on tubes ........ E717-500, -50110mm (3/8 ") diameter head-on tubes ......... E1761-21, -2213mm (1/2 ") diameter head-on tubes ......... E849-52, -9019mm (3/4 ") diameter head-on tubes ......... E974-17, -18, -2225mm (1 ") diameter head-on tubes ............ E2924-50028mm (1-1/8 ") diameter head-on tubes ...... E990-500, E2624-50052mm (2 ") diameter head-on tubes ............ E2979-501, E5859-01, -05

Besides those listed above, D-type socket assemblies specifically designed for use with coolers are provided.Please contact our sales office.

For C659 series coolers .............................. E1135-500, -501, -502, -503, -504For C4877 series coolers ............................ E2762-502, -504, -506, -509,- 510

We also have the C6270, which has built-in high voltage power supply with divider, for 28 mm (1-1/8 ") diameterside-on photomultiplier tubes.

D-type Socket Assemblies

27

Subject to local technical requirements and regulations, availability of products included in thispromotional material may vary.Please consult with our sales office.

High voltage power supplies and otherproducts contained in this brochuregenerate or exhibit hazardous voltage andmay present an electric shock hazard.

The products contained in this brochureshould be installed, operated, orserviced only by qualified personnel thathave been instructed in handling highvoltages.

The products contained in this brochureshould be installed, operated, or servicedin accordance with what are instructed intheir instruction manuals and other relevantHamamatsu publications.

Designs of equipment utilizing the productscontained in this brochure shouldincorporate appropriate interlocks toprotect the operator and service personnelfrom electric shocks.

HIGHVOLTAGE

WARNING

Type No. Wavelength Region Configuration Spectral Response Effective Area Maximum(nm) (mm) Supply Voltage (V)

R7154P

R1259P

R7207-01

R585

R3235-01

R3809U-52

R6350P

R6353P

R1527P

R2693P

R4220P

R5983P

R1635P

R647P

R2557

R7400P

R2295

R5610

R1924P

R3550

R7205-01

R6095P

R464

R329P

R3234-01

R7400P-01

R1878

R7206-01

R2228P

R649

R2257P

R3310-02

R1463P

R1104P

R943-02

R3809U-50

R6358P

R4632

R928P

R2949

R636P

R2658P

VUV to UV

UV to Visible

Visible

Visible to Near-Infrared

UV to Near-Infrared

28mm side-on

28mm side-on

28mm head-on

52mm head-on

52mm head-on

MCP-PMT

13mm side-on

13mm side-on

28mm side-on

28mm side-on

28mm side-on

28mm side-on

10mm head-on

13mm head-on

13mm head-on

16mm head-on

19mm head-on

19mm head-on

25mm head-on

25mm head-on

28mm head-on

28mm head-on

52mm head-on

52mm head-on

52mm head-on

16mm head-on

19mm head-on

28mm head-on

28mm head-on

52mm head-on

52mm head-on

52mm head-on

13mm head-on

28mm head-on

52mm head-on

MCP-PMT

13mm side-on

28mm side-on

28mm side-on

28mm side-on

28mm side-on

28mm side-on

160 to 320

115 to 195

160 to 650

160 to 650

160 to 650

160 to 650

185 to 650

185 to 680

185 to 680

185 to 650

185 to 710

185 to 710

300 to 650

300 to 650

300 to 650

300 to 650

300 to 650

300 to 650

300 to 650

300 to 650

300 to 650

300 to 650

300 to 650

300 to 650

300 to 650

300 to 850

300 to 850

300 to 850

300 to 900

300 to 850

300 to 900

300 to 1010

185 to 850

185 to 850

160 to 930

160 to 850

185 to 830

185 to 850

185 to 900

185 to 900

185 to 930

185 to 1010

8×24

8×14

φ 10

5×8

φ 10

φ 11

4×13

4×13

8×24

18×16

8×24

10×24

φ 8

φ 10

φ 10

φ 8

φ 4

φ 15

φ 21

φ 21

φ 10

φ 25

5×8

φ 46

φ 10

φ 8

φ 4

φ 10

φ 25

5×8

φ 46

10×10

φ 10

φ 25

10×10

φ 11

4×13

8×24

8×24

8×6

3×12

3×12

35

24

22

22

22

18

20

23

19

22

23

23

26

26

20

21

22

20

26

20

22

28

22

26

2219

0.19200.3200.461200.38213

0.25220.3230.3221218724132611252.7252.724814

0.13

220

120

420

390

390

390

270

330

300

270

320

320

390

390

375

360

390

375

390

375

420

390

390

390

390370800340800420800600800340800600800340

1000270800270800300800420600240600270600260800260800330800330

1000

1250

1250

1500

1500

2500

3400

1250

1250

1250

1250

1250

1250

1500

1250

1500

1000

1250

1250

1250

1250

1500

1000

1500

2700

2500

1000

1250

1500

1500

1500

2500

2200

1250

1500

2200

3400

1250

1250

1250

1250

1500

1500

QE Peak (%) Wavelength (nm)

Photocathode QE

Characteristics are measured at a supply voltage giving a gain of 2×105. Characteristics are measured at 1500V regardless of gain.

Table 1 : Typical Photomultiplier Tubes for Photon Counting

AB

28

700

900

770

800

1500

3000 A

750

800

780

900

720

720

1200

900

1000

800

900

850

1000

800

770

900

1000

1500

1500

800

1100

770

1100

800

1700

1700

1000

750

1700

3000 A

830

830

720

720

1300

1500 B

5

5

10

5

50

10

10

5

10

15

10

10

100

80

10

80

5

15

100

20

10

100

5

200

50

500

100

300

150

200

600

30

900

4500

20

200

20

50

500

3003

15

50

20

20

30

15

150

−30

10

50

50

50

50

400

400

30

40015

45

300

60

30

250

15

600

150

1000

250

1000

500

350

2000

150

1000

7000

50

−

50

100

1000

500−

50

300

25

25

25

25

25

25

25

25

25

25

25

25

25

25

25

25

25

25

25

25

25

25

25

25

25

25

25

25

−20

25

−20

−20

25

25

−20

25

25

25

25

25−20

−20

−20

2.2

2.2

1.7

13.0

1.3

0.15

1.4

1.4

2.2

1.2

2.2

2.2

0.8

2.5

2.2

0.78

2.5

1.5

2.0

2.0

1.7

4.0

13.0

2.6

1.3

0.78

2.5

1.7

15.0

13.0

2.6

3.0

2.5

15.0

3.0

0.15

1.4

2.2

2.2

2.2

2.0

2.0

1.2

1.2

1.2

−0.45

0.025

0.75

0.75

1.2

1.0

1.2

1.2

0.7

1.6

−0.23

1.0

−−−

1.2

−−

1.0

0.45

0.23

1.0

1.2

−

−

1.0

−

−

−

−

0.025

0.75

1.2

1.2

1.2

1.2

1.2

MgF2 R1220P

Low Dark Counts

R585S (Max.3 s-1) available

Fast Time Response

Fast Time Response

Compact , Low Dark Counts

Compact , High Sensitivity Low Dark Count

Low Dark Counts

Semitransparent Photocathode

High Sensitivity , Low Dark Counts

Wide Photocathode Area

Smallest Diameter

Low Noise Bialkali Photocathode

Metal Package , Compact , Low Profile

Low Afterpulse

Compact , Ruggedized

Ruggedized , Low Profile

Low Profile

Low Dark Counts

Replace R268P

R464S (Max.3 s-1) available

Fast Time Response

Metal Package

Low Dark Counts

Low Dark Counts

Extended-Red Multialkali Photocathode

R649S (Max.100 s-1) available

Extended-Red Multialkali Photocathode

High Quantum Efficiency (at 1µm)

High Gain

For Raman Spectroscopy

Fast Time Response

Compact , Low Dark Counts

Low Dark Counts

For near IR range , low dark count

For UV to 1010 nm range

R7154P

R1259P

R7207-01

R585

R3235-01

R3809U-52

R6350P

R6353P

R1527P

R2693P

R4220P

R5983P

R1635P

R647P

R2557

R7400P

R2295

R5610

R1924P

R3550

R7205-01

R6095P

R464

R329P

R3234-01

R7400P-01

R1878

R7206-01

R2228P

R649

R2257P

R3310-02

R1463P

R1104P

R943-02

R3809U-50

R6358P

R4632

R928P

R2949

R636P

R2658P

Supply Voltage Rise Time TTS Remarks Type No.(at 1×106 gain) (ns) (ns)Dark Counts

Typ. (s-1) Max. (s-1) Temp. ( C)

29

Main ProductsElectron TubesPhotomultiplier Tubes & AccessoriesLight SourcesMicrofocus X-ray SourcesImage IntensifiersX-Ray Image IntensifiersMicrochannel PlatesFiber Optic Plates

Opto-semiconductorsSi PhotodiodesSi PIN PhotodiodesSi APDsGaAsP PhotodiodesPhoto ICsImage SensorsPosition Sensitive DetectorsPhototransistorsInfrared DetectorsCdS Photoconductive CellsPhotocouplersSolid State Emitters

Imaging and Processing SystemsVideo Cameras for MeasurementImage Processing SystemsStreak CamerasOptical Measurement SystemsImaging and Analysis Systems

HAMAMATSU PHOTONICS K.K., Electron Tube Center314-5, Shimokanzo, Toyooka-village, Iwata-gun, Shizuoka-ken, 438-0193 JapanTelephone: (81)539/62-5248, Fax: (81)539/62-2205http :// www. hamamatsu. com

Danish OfficeErantisvej 5DK-8381 Tilst, DenmarkTelephone: (45)4346/6333, Fax: (45)4346/6350E-mail: lkoldbaek@hamamatus.de

Netherland OfficePO Box 50. 075, 1305 AB Almere The NetherlandTelephone: (31)36-5382123, Fax: (31)36-5382124E-mail: hamamatsu_NL@compuserve.com

North Europe:HAMAMATSU PHOTONICS NORDEN ABSmidesvägen 12SE-171 41 Solna, SwedenTelephone: (46)8-509-031-00, Fax: (46)8-509-031-01E-mail: info@hamamatsu.se

Italy:HAMAMATSU PHOTONICS ITALIA S.R.L.Strada della Moia, 1/E20020 Arese, (Milano), ItalyTelephone: (39)02-935 81 733Fax: (39)02-935 81 741E-mail: info@hamamatsu.it

Hong Kong:HAKUTO ENTERPRISES LTD.Room 404, Block B,Seaview Estate, Watson Road,North Point, Hong KongTelephone: (852)25125729, Fax: (852)28073155

Taiwan:HAKUTO Taiwan Ltd.3F-6, No.188, Section 5, Nanking East RoadTaipei, Taiwan R.O.C.Telephone: (886)2-2753-0188Fax: (886)2-2746-5282

KORYO ELECTRONICS CO., LTD.9F-7, No.79, Hsin Tai Wu RoadSec.1, Hsi-Chih, Taipei, Taiwan, R.O.C.Telephone: (886)2-2698-1143Fax: (886)2-2698-1147

Republic of Korea:SANGKI TRADING CO., LTD.Suite 431, World Vision Bldg.,24-2, Yoido Dong, Youngdeungpo-ku,Seoul,150-010 Republic of KoreaTelephone: (82)2-780-8515Fax: (82)2-784-6062

Singapore:HAKUTO SINGAPORE PTE. LTD.Block 2, Kaki Bukit Avenue 1, #04-01 to #04-04Kaki Bukit Industrial Estate, Singapore 417938Telephone: (65)7458910,Fax: (65)7418201

Quality, technology, and service are part of every product.

TPHO9001E03APR.2001 ZOPrinted in Japan (2000)

Information in this catalog isbelieved to be reliable. However,no responsivility is assumed forpossible inaccuracies or omission.Specifications are subject tochange without notice. No patentrights are granted to any of thecircuits described herein.

©2001 Hamamatsu Photonics K.K.

ASIA:HAMAMATSU PHOTONICS K.K.325-6, Sunayama-cho,Hamamatsu City, 430-8587, JapanTelephone: (81)53-452-2141, Fax: (81)53-456-7889

U.S.A.:HAMAMATSU CORPORATIONMain Office360 Foothill Road, P.O. BOX 6910,Bridgewater, N.J. 08807-0910, U.S.A.Telephone: (1)908-231-0960, Fax: (1)908-231-1218E-mail: usa@hamamatsu.com

Western U.S.A. OfficeSuite 110, 2875 Moorpark AvenueSan Jose, CA 95128, U.S.A.Telephone: (1)408-261-2022, Fax: (1)408-261-2522E-mail: usa@hamamatsu.com

United Kingdom:HAMAMATSU PHOTONICS UK LIMITED2 Howard Court, 10 Tewin Road Welwyn Garden CityHerffordshire AL7 1BW, United KingdomTelephone: 44-(0)1707-294888, Fax: 44-(0)1707-325777E-mail: info@hamamatsu.co.uk

France, Portugal, Belgiun, Switzerland, Spain:HAMAMATSU PHOTONICS FRANCE S.A.R.L.8, Rue du Saule Trapu, Parc du Moulin de Massy,91882 Massy Cedex, FranceTelephone: (33)169 53 71 00Fax: (33)169 53 71 10E-mail: infos@hamamatsu.fr

Swiss Office:Richtersmattweg 6aCH-3054 Schüpfen, SwitzerlandTelephone: (41)31/879 70 70,Fax: (41)31/879 18 74E-mail: swiss@hamamatsu.ch

Belgiun Office:7, Rue du BosquetB-1348 Louvain-La-Neuve, BelgiumTelephone: (32)10 45 63 34,Fax: (32)10 45 63 67E-mail: epirson@hamamatsu.com

Spanish Office:Centro de Empresas de Nuevas TecnologiesParque Tecnologico del Valles08290 CERDANYOLA, (Barcelona) SpainTelephone: (34)93 582 44 30,Fax: (34)93 582 44 31E-mail: spain@hamamatsu.com

Germany, Denmark, Netherland:HAMAMATSU PHOTONICS DEUTSCHLAND GmbHArzbergerstr. 10,D-82211 Herrsching am Ammersee, GermanyTelephone: (49)8152-375-0, Fax: (49)8152-2658E-mail: info@hamamatsu.de

Sales Offices

IBM-PC/AT is registered trademark of IBM Co. Windows is registered trademark of Microsoft Corporation in the U.S.A.