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Spectroscopic Light Sources

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Presentation on theme: "Spectroscopic Light Sources"— Presentation transcript:

1 Spectroscopic Light Sources
1. Continuum Sources 2. Line Sources 3. Quasi-continuum Sources

2 Source Types

3 Source Characteristics

4 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.

5 Spectral Radiance of a Black Body

6 Continuum Sources

7 Continuum Sources

8 Tungsten Lamps

9 1. Absorption Filters Optical material containing an absorber that permits transmission only at certain wavelengths


11 Reflection Grating:




15 Linear Dispersion Dl Dl = f × Da = dx/dλ where: f = focal length (of monochromator) x = distance (along focal plane)

16 Spectral Bandpass (s or Δλ) s = RLD × w where: w = slit width (mm) s in nm Reciprocal Linear Dispersion (RLD) RLD = Dl-1 =dλ/dx nm/mm



19 3. Si Photodiode Si: 3s23p2 Covalent Bonds in Solid
Therefore 1/2–filled sp3 ΔE ≤ 2.5 eV (semiconductor) 4 electrons fill a valence band at 0K At higher T an electron can move to conduction band Leaving a positive hole behind (both are mobile)

20 3. Si Photodiode Doping Si with a group 5 element (As or Sb) results
in extra electrons (n-type). Doping with a group 3 element (In, Ga) results in extra holes (p-type)

21 3. Si Photodiode

22 3. Si Photodiode Forward bias (not very useful for spectroscopy)

23 3. Si Photodiode Reversed Bias: Depletion zone at the junction.
Photons may eject electrons and form holes Current proportional to number of photons

24 3. Si Photodiode 200 – 1000 nm 1-10 ns response time 0.05 A/W


26 4. Linear Photodiode Array
200 – 1000 nm 1-10 ns response time 0.05 A/W

27 4. Linear Photodiode Array

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