Spectrochemical Instrumentation Modules 1. Light Source 2. Optical Components 3. Sampling Device 4. Wavelength Selector 5. Detector 6. Signal Processor
Mar 31, 2015
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