Investigation of cold cathode and RF excitation for long life CO2 waveguide lasers

Document describes a Ag-Li compound cathode for the longitudinally d.c. excited, low power, CO2 waveguide laser. Discharge tube results with this cathode produced an acceptable gas composition over a period of 1000 hours. The sputtering rate was quite low and, most importantly, the sputtering products did adhere quite well in the form of a thin film on the closest, cooler surfaces. A laser, using two of these cathodes, still produced 72% of its initial power output after 9200 hours of continuous service. Failure analysis indicated internal mirror damage on one of the mirrors, most likely due to improper selection of the dielectric top layer. Considerably more sputtering took place in the laser than in the discharge tube due to a laser cathode temperature that was too low. In parallel with these efforts we have started to investigate the life potential of the transversely R.F. excited waveguide laser. Preliminary results are quite encouraging. These tests were carried out over periods close to 3000 hours and indicate that proper selection of electrode materials is quite important. A wave guide laser with one of the waveguide sides made from a platinum alloy still yields 74% of its initial 2.85W after 5200 hours of continuous operations.