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