New trend in the technology of cw RF-excited sealed CO2 waveguide lasers

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Abstract
An investigation and optimization of a single channel transverse RF excited CW sealed CO2 waveguide laser is presented. The laser performance has been studied as a function of various parameters like the excitation frequency, gas pressure, gas mixture composition, and cooling temperature for two pairs of metal electrodes with equivalent sizes, but made of different material - gold plated copper and aluminum. The waveguide structure used was metal-ceramic with an active discharge volume of 2.5X2.5X370 mm3. Single-pass small-signal gain measurements for the two sets of electrodes have been performed, as well. The experiments show that the influence of the electrode material on the laser behavior is significant, while it was generally accepted as a factor of no importance. The best result we obtained with the Al electrodes was a specific output power of 0.78 W/cm with an efficiency of 11% at 125 MHz excitation frequency and 140 Torr of 1:1:5+5% (CO2:N2:He+Xe) gas mixture, which is very close to the highest specific power of 0.85 W/cm, previously reported. With the gold plated electrodes a specific output power of 1.1 W/cm with an efficiency of about 13% was achieved at 190 MHz and 100 Torr 1:1:5+5% gas mixture. This improvement is most likely related to the catalytic properties of the gold layers. This favorable process is accelerated at elevated temperatures, so that an intensive cooling is not necessary for good laser performance. The gain measurements confirmed this behavior. With gold plated electrodes at certain experimental conditions an increase of the gain of a factor 2 was observed.

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