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

Continuum Sources

Continuum Sources

Tungsten Lamps

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

Reflection Grating:

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

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

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)

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)

3. Si Photodiode

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

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

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

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

4. Linear Photodiode Array