1. Wavelength Selection Devices
1. Absorption Filters
2. Interference Filters
3. Prism Monochromators
4. Grating Monochromators
5. Interferometers

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

8. 2. Interference Filter
A “sandwich” of at least two parallel optical flats that transmit only rays that undergo constructive interference.

12. 3. Prism Monochromator
Wavelength selection device containing a movable prism.

14. Snell’s Law of Refraction
n1sin Θ1 = n2sin Θ2

18. 4. Grating Monochromator
Wavelength selection device based on the constructive interference of light rays that have traveled different differences to reach the same point.
Work via:
(1) transmission, or
(2) reflection

21. Reflection Grating:

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

26. 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

31. Camera
Echelle
prism
ICP

32. Rowland Circle

33. Limitations??

34. 5. Interferometer
Allows multiple wavelengths to fall on the detector simultaneously.
Corrects for interference patterns to calculate the signal at different wavelengths.

35. Fabrey-Perot Interferometer

37. Michelson Interferometer

39. Interferometer Advantages
1. Fellget’s Advantage (multiplex)
2. Jacquinot’s Advantage (throughput)
3. Wavelength Accuracy

40. Interferometer Disadvantages
1. Fellget’s Disadvantage (multiplex)
2. Low wavelengths
3. $$$ for high resolution