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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.

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Spectroscopic light sources

Spectroscopic Light Sources

1. Continuum Sources

2. Line Sources

3. Quasi-continuum Sources




Continuum sources

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.






1. Absorption Filters

Optical material containing an absorber that permits transmission only at certain wavelengths



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)

3. Si Photodiode

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 photodiode1

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 photodiode3

3. Si Photodiode

Forward bias (not very useful for spectroscopy)


3 si photodiode4

Reversed Bias:

Depletion zone at the

junction.

Photons may eject

electrons and form

holes

Current proportional

to number of photons

3. Si Photodiode


3 si photodiode5

200 – 1000 nm

1-10 ns response time

0.05 A/W

3. Si Photodiode


4 linear photodiode array

4. Linear Photodiode Array

200 – 1000 nm

1-10 ns response time

0.05 A/W



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