Spectrochemical Instrumentation Modules

1. Light Source

2. Optical Components

3. Sampling Device

4. Wavelength Selector

5. Detector

6. Signal Processor

Spectrochemical Instrumentation Modules

Source Wavelength Selector DetectorSignal Processor

ReadoutSample

Source

Wavelength Selector DetectorSignal Processor

ReadoutSample

0-90o

Spectroscopic Light Sources

1. Continuum Sources

2. Line Sources

3. Quasi-continuum Sources

Source Types

Source Characteristics

Continuum Sources

Emit radiation over a broad spectral range.

Continuum in Wavelength, not necessarily in time.

Most of these are “black body emitters. The spectral range depends upon the temperature of the black body.

Spectral Radiance of a Black Body

-4

-3

-2

-1

0

1

2

2.3 2.4 2.5 2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7

Log Wavelength (nm)

Lo

g B

(W

cm

-2 s

r-1

nm

-1)

1000

2000

3000

4000

5000

6000

7000

80009000

1000011000

Continuum Sources

Continuum Sources

Nernst Glower

Globars

Tungsten Lamps

Hydrogen or Deuterium Lamp

Current through low pressure H2 or D2

Fused silica window160-400 nm

Xenon Lamps

Pass current through high pressure Xenon Gas200-1000 nm output, sapphire windowProvide high intensity, but with high noise

Line Sources

Emit intense radiation over a narrow spectral range (or line).

The Full Width at Half Maximum (FWHM) for these sources is:

FWHM ≤ 0.01 nm

Typical of Line Sources

1. Low pressure pen lamps (Hg pen lamp)

2. Hollow Cathode Lamp (HCL)

3. Electrode-less Discharge Lamp (EDL)

Pen Lamps

Low pressure metal vapor inside an electrical discharge

Spectra characteristic of the metal vapor

Often used for calibration purposes

Hg Calibration Spectrum

Hollow Cathode Lamps

Cylindrical Cathode containing metal of interestLow pressure inert gas atmosphereProduces spectrum of cathode metal

Hollow Cathode Lamp Spectrum

Electrode Discharge Lamps

Metal salt in inert atmosphereAtomized and excited by RF field10 x stronger than HCL for volatile metals