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Introduction to opticalspectroscopy
Chemistry 243
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Fundamentals of
electromagnetic radiation
(s-1)
34Planck's constant 6.626 10 J s
=frequency in Hz
E h
h
ν
ν
−
=
= = × ×
8 msee! of li"#t 3.00 10s
=$a%elen"t#
c
c
ν
λ
λ
=
= = ×
E swavenumber cm ∝∝== − υ
λ
11
ν h E = ν λ =
c
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Electromagnetic spectrum
http://www.yorku.ca/eye/spectrum.gif
HighEnergy
LowEnergy
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Terminology Spectroscopy is the study of the interaction of
light and matter NMR or !Ray spectroscopy" spectroscopist
Spectrometry is the esta#lishment of thepattern of interaction $as a function of energy% of
light with particular forms of matter Mass spectrometry $M&%" spectrometrist
Spectrophotometry is the 'uantitati(e study of
the interaction of light with matter )*!*isi#le spectrophotometry (I’e neer heard anyone called a spectrophotometrist)
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!hat chemical and"or material
properties can we measure using
spectral methods# +road and powerful applications ,lemental composition $often metals" C-N% dentity of a pure su#stance $what is it0% Components of a mi1ture $purity0% mount of a su#stance in a mi1ture $how much0% +ulk/maor component minor component
trace component ultra!trace component &urface composition Material property $stress/strain polymer cross!
linking change of state temperature% Reaction rate mechanism products
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!hat properties of incident or
generated light can we measure#
#sorption 5luorescence $fast% 6 7hosphorescence $slow% 8hermal ,mission
Chemiluminescence &cattering Refraction or Refracti(e nde1 7olari9ation 7hase nterference/iffraction Coherence Chemistry conse'uent to the a#o(e
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!hat atomic"molecular properties
affect or are affected $y light#
Rotation $typically refers to a molecule%
*i#ration $typically refers to a molecule%
,lectronic ,1citation $atomic or molecular% oni9ation $loss of electron to yield a cation%
Com#inations of the a#o(e:
Rotation!(i#ration $infrared/Raman% Rotational (i#rational electron e1citation $)*!*is%
oni9ation with )* a#sor#ance $strong e1citation%
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The properties you want to study
help to select a suita$le waelength
-igh ,nergy
;ow ,nergy
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!hy waenum$er#
8he energy difference #etween two wa(enum#ers isthe same regardless of spectral region or λ
<a(elength is not proportional to energy" it has a
reciprocal relation to energy so:
8he energy difference #etween two wa(elengths $in nmor angstroms% (aries as a function of spectral region.
11 −=⇒= cmunit
λ ν
&' ν
ν
λ
ν
∆=∆
==
=
hc E
hc
hc
h E
ν λ =c
E ∝λ
1
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%electing the right optical
method
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Emission
&lasma'
flame' or
chemical
Focus
%orting of
Energy'
%pace' and
Time
etection
Computer control enhances
and optimi9es the info
e1tracted from each
instrument component.
,1citation &ource
Chemiluminescence is emission
caused #y a chemical reaction.
5luorescence is emission
caused #y e1citation
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$sorption
Light
%ource Focus %pecimen FocusEnergy'
%pace' and
Time %orting
etection
Transmissionand"or
*eflection can
also occur
Nearly linear light path geometry
for multi!wa(elength
simultaneous light detection
Rela1ation is non!radiati(e"sample warms up a #it (ia (i#ration and rotation
) $ s o r $ a n c e
!aelength (+)
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Fluorescence (fast) , &hosphorescence
(slow)
Light%ource
(Laser)
Focus
Focus etection
%pecimen
Energy'
%pace' and
Time %orting
ay include
energy sorting
Typical geometry ./0'
$ut angle aria$le
E m i s s i o n & o w e r
*adiatie
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*aman %cattering
Light
%ource
Laser
Focus
Focus etection
%pecimen
Energy'
%pace' and
Time %orting
Typical geometry ./0'
$ut angle aria$le
%ame geometrical layout as fluorescence and phosphorescence'
2ut what happens is not the same as a$sorption or emission
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*aman %cattering
Elastic scattering3 Ee4 5 Eout
Inelastic scattering3 Ein 6 Eout and Ein 7 EoutEe4citation
Ee4 8E-E
irtual stateirtual state
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,mission
5lame
plasma
chemistry
#sor#ance$)*/*is or R%;amps ;,s
5luorescence/
7hosphoresence
;amps ;,s
laserslasers
Raman scattering
ifferent classes of optical
spectroscopy
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9lasses of light sources
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Light sources3
9ommon e4amples
+lack#ody radiation ;ight emitting diode $;,s% rc lamp/hollow cathode lamp
;asers &olid!state =as/e1cimer ye laser
8hermal e1citation Com#inations $laser to (apori9e
sample leading to thermal emission%
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9ontinuum spectra and
$lac:$ody radiation
solid is heated to incandescence t emits thermal #lack#ody radiation in a continuum
of wa(elengths
%:oog' Fig; <-==
High E 5 Low + 5 High T <ien>s
;aw
b is <ein>s displacement constant
6
6
6
2.8(8 10 ) nm
2.8(8 10 ) nm(.82 m
2(* )
2.8(8 10 ) nm(.3* m
310 )
peak
roomtemp
human
T λ
λ µ
λ µ
× ×=
× ×= =
× ×= =
T bblackbody
peak =λ
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9ontinuum spectra and
$lac:$ody radiation
http://en.wikipedia.org/wiki/mage:+lack#ody!lg.png
http://en.wikipedia.org/wiki/+lack?#ody
8 @ A2BB C8 @ A4D3 E
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9ontinuum sources
Common sources euterium lamp $common )ltra(iolet source% r e or -g lamps $)*!(is%
>ot always continuous" spectral structure possi#le
http://wwwA.union.edu/newman/lasers/;ightF2B7roduction/;amp&pectra.gif
http://creati(elightingllc.info/4GBp1!euterium?lamp?A.png
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Light emitting diodes (LEs)
5irst practical (isi#le region ;,
in(ented #y Nick -olonyak in
AHI2 $=," ))C since AHI3%
J5ather of the light!emitting!diodeK
http://en.wikipedia.org/wiki/Nick?-olonyakhttp://upload.wikimedia.org/wikipedia/commons/D/Dc/7nLunction!;,!,.7N=
http://www.pti!n.com/images/8imeMaster;,/;,!spectra?remade.gif
n ;, is a semiconductor
which emits electroluminescence
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Light emitting diodes (LEs)
Cheap low energy long!lasting small fast
Commonly used in display screens stoplights
circuit #oards as state indicators
;ots of colors nfrared ;,s used in remote controls
http://en.wikipedia.org/wiki/5ile:*erschiedene?;,s.pg
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Line (emission) sources
Continuous wa(e -ollow cathode discharge lamp
Microwa(e discharge
5lames and argon plasmas
7ulsed 7ulsed hollow cathode
&park discharge ll these are non!laser
line source is a light source
that emits at a narrow waelengthcalled an emission ?line@
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Lasers
Light mplification #y
%timulated Emission
of *adiation
• ntense light source• Narrow #andwidth $small range B.BA nm%• Coherent light $in phase%
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Lasers
Light mplification #y
%timulated Emission
of *adiation
• 7umping
• &pontaneous ,mission• &timulated ,mission• 7opulation n(ersion
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Laser design
Lasing medium is often3• a crystal' li:e ru$y• a dye solution• a gas or plasma
photon
cascadeA
&koog 5ig. D!4
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&umping
=eneration of e1cited electronic states #y thermal
optical or chemical means.
&koog 5ig. D!G
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%pontaneous emission or
rela4ation
Random in time No directionality
Monochromatic $same % #ut incoherent $not in phase%
&olid (s. dashed line O 2 different photons
&koog 5ig. D!G
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%timulated emission
8he e1cited state is struck #y photons of precisely
the same energy causing immediate rela1ation
,mission is 9BHE*E>T
,mitted photons tra(el in same direction ,mitted photons are precisely in phase
&koog 5ig. D!G
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&opulation inersion
<hen the population
of e1cited state
species is greater
than ground statean incoming photon
will lead to more
stimulated emission
instead ofa#sorption. Inerted population
>ormal population
distri$ution
&e4cited 7 &ground
&e4cited 6 &ground
&koog 5ig. D!I
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C- and D-state lasers
7opulation in(ersion easier in 4!state system
&koog 5ig. D!D
Things stac:
up here;
&opulation
inersion easily
achieed;
&opulation
relatiely low
down here
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Laser design
Lasing medium is often3• a crystal' li:e ru$y• a dye solution• a gas or plasma
photon
cascadeA
&koog 5ig. D!4
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9ontinuous wae
laser sources Nd3P:Qttrium aluminum garnet $Q=: Q3 lGA2%
&olid state 1/<D nm C= nm 3GG nm 2II nm
8he =8, &yl(ania Model IBG uses a Nd!Q= laser rod set in a dou#leellipticalJ reflector is pumped #y two GBB!< incandescent lamps and is
limited to a low order mode #y an aperture in the laser ca(ity.
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9ontinuous wae
laser sources -elium!Neon $-eNe%
=as #ut emission comes from generated plasma $(ery e1citedstate atoms%
<C=; nm IA2 nm IB3 nm and G43.G nm" A.AG 6 3.3H Sm ,mission lines all the way out to ABB Sm
HH.HF
reflecti(e
HHF
reflecti(e
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9ontinuous wae
laser sources rP
=as laser #ut emission comes from ions )ses lots of electrical power to generate ions
3GA.A nm 3I3.T nm 4G4.I nm 4GD.H nm 4IG.T nm 4DI.G nmD;/ nm 4HI.G nm GBA.D nm 1D; nm G2T.D nm ABH2.3 n
Coherent nno(a HB
)p to G < of outputU
VABB1 my laser pointer
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Bther continuous wae
laser sources
Cu (apor G2B nm
-eCd
DD/ nm 32G nm ye lasers
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&ulsed lasers sources Nd:Q=
&olid state
ften nanosecond pulses
1/<D nm' C= nm 3GG nm
8i:sapphire &olid stateWoften pumped #y Nd:Q=
8una#le output aroudn TBB!A2BB nm
7roduces femtosecond pulses
Nitrogen =as
CCG nm
,1cimer lasers $gas mi1tures" e1cited state is sta#le%
8una#le dye lasers $ is selecti(e within limits%
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Laser diodes
)sed in C and *players $not (ery strong%
<a(elengths now a(aila#lefrom R to near )* regions
+and gap
energy ,g
&koog 5igs. D!T 6 D!H.
*esonant
9aity emits
t .G nm
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Tip going forward
Eeep your (aria#les straight v for (elocity or ν for fre'uency
Microsoft e'uation editor gi(es:
will use m for integer te1t#ook uses n ,asy to get mi1ed up with refracti(e inde1 n
m+s& %ee
1+s&nu
=
=
v
ν
& ti f l t ti
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&roperties of electromagnetic
radiation
8ransmission
Refraction
Reflection &cattering
ptical Components
nterference
iffraction
& ti f l t ti
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&roperties of electromagnetic
radiation
y = magnitude of the electric field at time t
A = ymax – also called the amplitude of y
ν = frequency in s -1 (cycles per second)
φ = phase angle (an offset relative to a reference sine wave)
ω = angular velocity in radians/sec (a handy definition)
Recall: π radians = 1! degrees
( )
( )φ πν
πν ω
φ ω
+=
=
+=
t A y
t A y
2sin
2
sin
φ
Interference magnitudes add or su$tract
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2
82
+ is in phase with
Interference magnitudes add or su$tract
Interference magnitudes add or su$tract
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2
82
+ is ATB degrees $X radians% shifted from
Interference magnitudes add or su$tract
Interference magnitudes add or su$tract
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2
82
+ is HB degrees $X / 2 radians% shifted from
Interference magnitudes add or su$tract
Interference $etween waes of
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Interference $etween waes of
different freuency
<a(e A P 2
&koog 5ig. I!G
21 ν ν ν −=∆
T i i th h
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Transmission through
materials Compared to (acuum the (elocity of light is reduced
when propagating through materials that ha(e
polari9a#le electrons. <a(elength also decreases
ll electrons are polari9a#le to some e1tent
%:oog' Fig <-=; cacuum 5 =;..G.= 4 1/ m Y s-1
i
i
cn
v=
me!iumc
constant
=
=
=
λν
ν h E
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Inde4 of *efraction
*efractie inde4 is measure of how much light is slowed3
*efractie inde4 is waelength- and temperature-dependent for many materials3
A.4IZuart9
A.4H8oluene
A.43-e1adecane
A.GT=lass$light flint%
A.33<ater
A.BB*acuum $air%
n @ 589.3 nmaterial<a(elength!dependence of nSiO2
http://www.rp!photonics.com/refracti(e?inde1.html
len"t#"i%en $a%eaat%elocity
1&'len"t#"i%en $a%eaatin!e,refracti%e
=
≥==
i
i
vacuumi
v
v
cn
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*efraction
&nell>s law:
il immersion lenses
for high magnificationmicroscopy
Jelocities' not freuencies
Medium A
Medium 2
Here' n= 7 n1
%:oog' Fig; <-1/
2
1
1
2
2
1
sin
sin
v
v
n
n==θ
θ
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For your information
+ook ,rror on page A4A e'uation I!A2:
8his is correct: &nell>s ;aw of Refraction
2me!iumin%elocity
1me!iumin%elocity
sin
sin
2
1
1
2
2
1 === v
v
n
n
θ
θ
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*eflection
mount of loss at a reflection increases with refracti(einde1 mismatch. 5or right angle light entrance into a medium:
Reflecti(e loss is angle!dependent
5resnel e'uations $which we will skip% Most important case is: total internal reflection
( )
( )
2
2 1
20 2 1
r n n I
I n n
−=
+ 1intensityinci!ent
intensityreflecte!≤=
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Total internal reflection
;ight incident upon a material
of lesser refracti(e inde1 is#ent away from the normal sothat the e1it angle is greaterthan then incident angle. t the critical incident angle
the e1it angle is HB ! #eam
does not e1it ngles larger than the critical
incident angle lead to totalinternal refection $8R%
MediumA
Medium2
nentry
ne4it
Modified from &koog
nentry 7 ne4it
K= 7 K1
!hen this is true' K1 5 critical entry angle for TI*
exit critical entry
exit critical entry
exit entry
nn
nn
nn
nn
=
=
=
=
θ
θ
θ θ
θ θ
sin
&(0sin'sin
sinsin
sinsin
21
2211
1θ
2θ
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Total internal reflection
8R fluorescence
microscopy:
http3""hyperphysics;phy-astr;gsu;edu"H$ase"phyopt"totint;htmlhttp3""www;olympusmicro;com"primer"techniues"fluorescence"tirf"tirfintro;html
!hen this is true'
K1 5 critical entry angle for TI*;
If K1 [ Kcritical result is TI*;
Eanescent wae samples a ery
narrow slice of the sample ery near
to the dielectric interface
Typically =// nm
exit critical entry nn =θ sin
f
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Total internal reflection
8R fluorescence
microscopy:
!hen this is true'
K1 5 critical entry angle for TI*;
If K1 [ Kcritical result is TI*;
http3""hyperphysics;phy-astr;gsu;edu"H$ase"phyopt"totint;htmlhttp3""www;olympusmicro;com"primer"techniues"fluorescence"tirf"tirfintro;html
Mood for studying adhered cellsN low $ac:ground
exit critical entry nn =θ sin
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Fi$er optics
,1truded strands of glassor plastic that guide light(ia total internal reflection. Core has higher refracti(e
inde1 than cladding. 5le1i#le Material choice allows
transmission in )* (isi#leor R
&koog 5ig D!3H.
Follows all the rules of
%nell’s Law
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%cattering
Raman scattering nelastic scattering
offset from λ #y fre'uency of molecular (i#rations
Rayleigh scattering Molecules or aggregates smaller than λ ntensity V A/λ4
Mie scattering 7articles large $or compara#le% to λ )sed for particle si9ing
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Essential optical elements
;enses
Mirrors
7risms
5ilters
=ratings
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2asic optical components
Mirrors Reflection
Conca(e mirror is
con(erging
7risms Refraction
&nell>s ;aw1 1 2 2sin sinn nθ θ =
Filt
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Filters
#sorption filters Cheap (isi#le region"
colored glass
Cutoff filters O long!pass
short!pass
nterference filters
%:oog' Fig; G-1=
θ is usually 9ero
so cos θ \ A.
lso m is usually A
d \ thickness of dielectric layer
n \ refracti(e inde1 of dielectric medium
m = inte"er
λ ́ = $a%elen"t# in t#e !ielectric material
2
cos
2
cos
inter"er
air
air
d m
n
dn
m
m
λ θ
λ λ
λ θ
′ =
′=
=
=
I t f filt
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Interference filters
lmost
monochromatic
%:oog' Fig; G-1C
2andwidth of a filter is
width at half-height(a:a full-width O half-ma4)
iffraction of coherent radiation3
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iffraction of coherent radiation3
Interference at wor:
Conse'uence of
interference
%:oog' Figs; <-G' <-
constructie
destructie
constructie
constructie
destructie
d 5 distance from slit 2 to 9
istance 4 to y is one +
(m is the order of interference)
m is3• / for E• 1 for
m use! #ere- te,t uses n
inte"er
sin
==
m
d m θ λ
iffraction of coherent radiation3
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act o o co e e t ad at o
Interference at wor:
Conse'uence of
interference
(m is the order of interference)
m use! #ere- te,t uses n
You can now determine the
wavelength of light
based on things that
are easy to measure!
%:oog' Fig; <-
inte"er
sin
==
m
d m θ λ
OD DE BC
d m
=
= θ λ sin
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onochromators
)sed to spatially separate different
wa(elengths of light: prisms gratings
C9erny!8urner grating monochromator +unsen prism monochromator
%:oog' Fig; G-1
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Mratings and monochromators
*eflection 8 diffraction3 echellette-type grating
%:oog' Fig; G-=1
The condition for
constructie interference;The m 5 1 line is most intense;
The surface contains ?grooes@ or ?$laPes@;
8ake a look at
,1ample D!A
7age AT4.
( )
( )
sinsin
sin sin
m CB BD
CB d i BD d r
m d i r
λ
λ
= +
=
=
= +
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onochromators
)sed to spatially separate different
wa(elengths of light: prisms gratings
C9erny!8urner grating monochromator
%:oog' Fig; G-1
Qseful metrics for
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Qseful metrics for
monochromators
ispersion $page ATG%" high dispersion is good ntegration of at constant i gi(es the
angular dispersion:
Linear dispersion is the (ariation of along the
focal plane position y:
*eciprocal linear dispersion !A:
r 5 angle of reflection
d 5 distance $etween $laPes
ore useful' results in
-1 in nm per mm
or similar
measure of
the a$ility to
separate waelengths
( )sin sinm d i r λ = +
cos
dr m
d d r λ =
focal len"t#
dy dr D
d d
λ λ
×= =
=
1 cos for small r
d d r d D
dy m m
λ − ×= = ≈
Qseful metrics for
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Qseful metrics for
monochromatorsRcontinued
Resol(ing power $R" unitless% ;imit of monochromator>s a#ility to distinguish
#etween adacent wa(elengths.
;ight gathering power $f!num#er 5" unitless% Collection efficiencyWimpro(e for ma1imi9ing &/N
,fficiency scales as the in(erse s'uare of 5
focal len"t# of collimatin" mirror or lens
!iameter of collimatin" otic
! d
d
=
=
=
!illuminate lazes"ratin"of /umer
'unitless&
=
=
∆
=
"
m" #λ
λ
2
∝
d E
9omplications with
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9omplications with
monochromators
(erlap of orders m \ A λ\ IBB nm and m \ 2 λ \ 3BB nm spatially o(erlap
Qou can get λ>s mi1ed up if light source contains manywa(elengths
dditional wa(elength selection often needed 5ilter prism detector selection de(ice digital
analysis after data collection #ackgroundsu#traction Might need to use a different light source if your
wa(elength of interest is not JcleanK
%lit width and spectral
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%lit width and spectral
resolution of a spectrometer
8radeoff e1ists #etween sensiti(ity and resolution -igh intensity \ high sensiti(ity $low noise%
8wo #asic concepts: f you make the entrance slit width too #ig you let in a lot of
light $that>s good O high intensity% #ut it can #e multi!wa(elength" a large section of light dispersed in λ is let in =ood light intensity poor spectral resolution
f you make the entrance slit width too small you let in less
light $less intensity% #ut its λ range is smaller 7oor light intensity good spectral resolution
,ntrance slit $creates image% and e1it slit $output filter% )sually the same width
ptimal slit width #ased upon grating dispersion
%lit width
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%lit width
&koog 5ig. D!24
For Sust passing =
%lit width
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&koog 5ig. D!2G
&total
If spectral $andwidth
is "=' good
spectral resolution
2oth entranceand e4it slits
narrowed
from top to
$ottom
%lit width
w is slit width
%lit width
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&koog 5ig. D!2I
%lit width
<atch the effect of adusting the slit width and theresultant spectral #andwidth on the following data sets of
#en9ene (apor.
w is slit
width
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Bptical &hotodetectors
. 7hotomultiplier tu#e $7M8%
+. Cd& photoconducti(ity
C. =as photo(oltaic cell
. Cd&e photoconducti(ity cell
,. &e/&e photo(oltaic cell
5. &i photodiode
=. 7#& photoconduciti(ity
-. 8hermocouple
. =olay cell
These generally ma:e current
or oltage when light hits them;
ore sensitie
Less sensitie
Ideal photodetector
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Ideal photodetector
(photon transducer)
-igh sensiti(ity
-igh &/N
5ast response time
&ignal directly
proportional to ] of
photons detected
^ero dark current 8he #lank is 9ero
r e'ui(alently
counte! P#otons∝ "
$
k% $ =
Ideal photodetector
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-igh sensiti(ity
-igh &/N
5ast response time
&ignal directly
proportional to ] of
photons detected
^ero dark current 8he #lank is 9ero
Ideal photodetector
(photon transducer)
-igh sensiti(ity
-igh &/N
5ast response time
&ignal directly
proportional to ] of
photons
^ero dark current
R e a l i t y
I n t r u
d e s -ere>s what really happens:
&ignal is
5unction of
Constant dark
current term
$non!9ero%
$ k% =
( ) dark $ k% k λ = +
Three main
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Three main
photodetector types
7hoton transducers $directly JcountK photons% 7hotomultiplier tu#es $7M8s%
Charge transfer de(ices
Charge inection de(ices $C% Charge coupled de(ices $CC%
8hermal transducers 7hotons strike the transducer
8emp increases 8emp increase increases conducti(ity
Current or (oltage are measured
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Jacuum phototu$e
Cathode is coated with
photo!emissi(e material
,mitted electrons are
collected anode.
] of electrons is directlyproportional to ] of photons.
Current is easy to amplify.
)sually ha(e small dark
current. perate at V HB* #ias
Not so porta#le
&koog 5ig. D!2H.
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&hotomultiplier tu$e (&T)
] of electrons is amplified#y photoelectric effectupon accelerationtowards dynodes
,ach dynode #iased V HB*more positi(e than pre(iousdynode $or cathode%
*oltage drop accelerateselectrons to dynode
cascade mplification: ABI!ABD
electrons per incidentphoton" electron cascade
http://www.nt.ntnu.no/users/flo#an/ELF2BF2B3BGG/7M8.pg
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&hotomultiplier tu$e (&T)
d(antages: *ery sensiti(e in )*!*is region
single photon sensiti(ity Cooled 7M8 has (ery low
#ackground $kdark approaches 9ero%
;inear response 5ast response
isad(antages ,asily damaged #y intense $am#ient%
light Noise is power dependent &ingle channel: can>t use for imaging
&hotooltaic cell
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&hotooltaic cell ;ight strikes a
semiconductor $&e% andgenerates electrons andholes
Magnitude of current isproportional to ] of
photons Re'uires no e1ternal
power supplyU isad(antages: hard to
amplify signal and fatigue$wears out% )seful for porta#le
analyses field workoutdoor setting
&koog 5ig. D!2T
&hotodiodes
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&hotodiodes(%ilicon 1./-11// nm' InMas .// 1<// nm)
Re(erse!#iased p!n unction Conductance goes to near
9ero
7hotons create electron hole
pairs that migrate to oppositecontacts and generate
current
+attery powered 7orta#le applications
re not as prone to some
electronic noise sources IB -9 line noise
&koog 5ig. D!32
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ultichannel transducers
llow simultaneous interrogation of multiple
wa(elengths
maging
7hotodiode arrays $A! array%
Charge!transfer de(ices $2! array% Charge!inection de(ices
Charge!coupled de(ice $CC% CM&
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&hotodiode arrays
,ach diode has definedspatial address
d(antages Multichannel $used for
imaging% More ro#ust than 7M8
isad(antages Not as sensiti(e as 7M8 &lower response time
Common in cheaper )*!*isinstruments ften perfectly ade'uate
&koog 5ig. D!33
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9harge transfer deices
Con(erts light into charge Negati(e!#iasing leads to
increased capture of holes
under pi1el electrodes 7otential well
7hoton eects electron and
the de(ice collects and stores
charges ABG!ABI charges per pi1el
Configured as C or CC
&koog 5ig. D!3G
&chematic is for C
9harge transfer deices
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g
(continued)
Charge!inection de(ice $C%!measuresaccumulated (oltage change $nondestructi(eread" persistent after read% Measurements can #e made while integrating
Charge!coupled de(ice $CC%!mo(esaccumulated charges to amplifier and readout$destructi(e read" gone after read% *ery high sensiti(ity" AB4!ABG pi1els
-igh resolution spectral imaging Complementary metal o1ide semiconductor
$CM&% <e#cam technology: C-,7U
E sensiti(ity large pi1el density
99 (charge coupled deice)
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99 (charge coupled deice)
7i1els read one at a time #y se'uential
transfer of accumulated charge
5rom: JCC (s. CM&: 5acts and 5ictionK #y a(e ;itwiller in 7hotonics &pectra Lanuary 2BBA
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9B% detectors
igital camera and we#cam technology
,ach pi1el can #e read indi(idually
5rom: JCC (s. CM&: 5acts and 5ictionK #y a(e ;itwiller in 7hotonics &pectra Lanuary 2BBAmage from <ikipedia
99 9B%
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99 9B%
,ssentially serial
,ach pi1el read one at atime #y common e1ternalcircuitry *oltage con(ersion and
#uffering
utputs an analog signal -istorically ga(e higher!
resolution images Relati(ely e1pensi(e
-igh power consumption )p to ABB1 more than
CM&
,ssentially parallel
,ach pi1el has its own redout circuitry Jon!chipK llows amplification and
noise correction More suscepti#le to noise
utputs a digital signal Reduced area for light
a#sorption Relati(ely ine1pensi(e
-ighly commerciali9ed fa#
Runs on less power Re'uires less Joff!chipK
circuitry
2oth approaches e4ist today
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&hotoconductiity transducers
&emiconductors whose resistance decreases
when they a#sor# light
#sorption promotes electron to conduction
#and. )seful in near R$λ \ B.DG to 3 µm%
Cooling allows e1tension to longer
wa(elengths #y reducing thermal noise
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Thermal transducers
&olution for R region $low energy photons%
8hermocouples ;ight a#sor#ed heats the unction $two pieces of dissimilar
metal% which leads to a change in (oltage relati(e to a
reference thermocouple.
+olometer $thermistor% Material changes resistance as a function of temp
7yroelectric de(ices 8emperature!dependent capacitor
Change in temperature leads to change in circuit current