spectroscopic light sources 1. continuum sources 2. line sources 3. quasi-continuum sources
TRANSCRIPT
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
-4
-3
-2
-1
0
1
2
2.3 2.4 2.5 2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7
Log Wavelength (nm)
Lo
g B
(W
cm
-2 s
r-1
nm
-1)
1000
2000
3000
4000
5000
6000
7000
80009000
1000011000
Continuum Sources
Continuum Sources
Tungsten Lamps
1. Absorption Filters
Optical material containing an absorber that permits transmission only at certain wavelengths
Reflection Grating:
Linear DispersionDl
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 LinearDispersion (RLD)
RLD = Dl-1
=dλ/dx
nm/mm
3. Si Photodiode
Si: 3s23p2
Covalent Bonds in Solid
Therefore 1/2–filledsp3
ΔE ≤ 2.5 eV(semiconductor)
4 electrons fill a valence band at 0KAt higher T an electron can move to conduction bandLeaving a positive hole behind (both are mobile)
3. Si Photodiode
Doping Si with a group 5element (As or Sb) resultsin extra electrons (n-type).
Doping with a group 3element (In, Ga) resultsin 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 thejunction.
Photons may eject electrons and formholes
Current proportionalto 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