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

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Presentation on theme: "Spectroscopic Light Sources 1. Continuum Sources 2. Line Sources 3. Quasi-continuum 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

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8 Tungsten Lamps

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

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11 Reflection Grating:

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15 Linear Dispersion D l D l = f × D a = 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 = D l -1 =dλ/dx nm/mm

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19 3. Si Photodiode Si: 3s 2 3p 2 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 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

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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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