Part A
A problem restricting the development of the CuCl laser has
been the decrease in output power with increases of tube temperature
above 400°C. At that temperature the CuCl vapor pressure is about
.1 torr. This is a small fraction of the buffer gas pressure (He at
10 torr).
The aim of the project was to measure the peak radiation temperature
(assumed related to the mean energy of electrons) in the
laser discharge as a function of the tube temperature. A 24 gHz gated
microwave radiometer was used.
It was found that at the tube temperatures at which the output
power began to deteriorate, the electron radiation temperature showed
a sharp increase (compared with radiation temperature in pure buffer).
Using the above result, we have postulated that this sudden increase
is a result of Penning ionization of the Cu atoms. As a consequence
of this process the number of Cu atoms available for lasing
decrease.
PART B
The aim of the project was to study the dissociation of CO2 in
the glow discharge of flowing CO2 lasers.
A TM011 microwave (3 gHz) cavity was used to measure the radially
averaged electron density ne and the electron-neutral collision frequency
in the laser discharge. An estimate of the electric field is made
from these two measurements. A gas chromatograph was used to measure
the chemical composition of the gases after going through the discharge.
This instrument was checked against a mass spectrometer for
accuracy and sensitivity.
Several typical laser mixtures were .used: CO2-N2-He (1,3,16),
(1,3,0), (1,0,16), (1,2,10), (1,2,0), (1,0,10), (2,3,15), (2,3,0),
(2,0,15), (1,3,16)+ H2O and pure CO2. Results show that for the conditions
studied the dissociation as a function of the electron density
is uniquely determined by the STP partial flow rate of CO2, regardless
of the amount of N2 and/or He present. The presence of water vapor in
the discharge decreased the degree of dissociation.
A simple theoretical model was developed using thermodynamic
equilibrium. The electrons were replaced in the calculations by a distributed
heat source.
The results are analyzed with a simple kinetic model.