INFICON Guardian EIES Controller - Manual (Page 126)

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Guardian Co-Deposition Controller Operating Manual
Within the sensor housing, electrons from the filament strike the evaporant atoms,
raising the energy level of the outer electrons. These excited electrons immediately
return to their normal energy level, emitting photons. The wavelength of the
photons is characteristic of the material, and the intensity is proportional to the
number density of the atoms.
For any material:
[1]
where:
J = Emission Intensity
i = Electron Beam Current
N = Number Density of Atoms
and:
[2]
where:
D = Mass Deposition Rate
m = Mass of Atom
v = Average Velocity of Atoms
Finally, for a constant velocity:
[3]
where:
k is a calibration constant.
The calibration constant incorporates several assumptions inherent in the above
derivation—constant velocity, constant source temperature, and optical losses.
The emitted light must be efficiently transmitted to the detection device(s). For
short, straight transmission paths from the sensor to the detector(s), the sensor's
hollow tube may be adequate. However, the number of photons reaching the
detector is proportional to the inverse of the light path squared (1/D
2 ).
For straight paths, a quartz light pipe placed inside the sensor 's hollow light tube
is inexpensive and simple to fabricate. For transmission of the UV wavelengths
used in EIES, a high-purity fused quartz guide is required. A quartz light guide can
provide nearly a factor of ten improvement in light transmission. For non-linear
paths, and efficient signal splitting, a fiber optic splitter allows flexibility in
sensor/detector placement, and significantly less optical loss.
J iN 
D mvN =
J kD =