Enhanced gain and output power of a sealed-off rf-excited CO2 waveguide laser with gold-plated electrodes

Abstract

The small-signal gain and the laser output power have been measured in a cw sealed-off rf-excited CO2 waveguide laser for two different electrode materials, gold-plated copper and aluminum, at several excitation frequencies, gas pressures and mixture compositions. In the case of the goldplated electrodes an enhancement of the gain up to a factor of 2 and the output power up to a factor of 1.4 with time at a frequency of 190 MHz and 60 Torr of 1:1:5+5% (C0,:N2:He+Xe) mixture is observed. This is believed to be the result of the gold catalytic activities which are favored by increased electrode temperatures and helium rich gas compositions.During the last two decades rf-excited COz waveguide lasers have received considerable attention1 because of their compactness, discharge stability, and high output power density of more than 1 W/cm.2 They are suitable for many applications where long sealed lifetime from a compact device is required. However, the high-power density in a rf discharge causes severe decomposition reactions of the initial COz:N2:He+Xe gas mixture. The main detrimental reactions to the laser performance that produce both the loss of COz and the buildup of O2 are COz+e--+CO+O+e and/or CO,+e-+CO+O-.

Theoretical and experimental investigation of a waveguide CO2 laser with radio-frequency excitation

“…As we already mentioned up till now a lot of experimental data with respect to the output energy of the r.f. excited CO2 laser has been published [28][29][30], however, there is practically no comparison with model calculations. Analysis of experimental data shows that they are sometimes contradictory in the sense that for the same active medium parameters (input power, excitation frequency, gas composition and pressure, electrode geometry) the laser power differs substantially.…”

“…Therefore, we will discuss only the best experimental results as obtained at Herriot Watt University (UK) [28] and in the groups at Twente University (The Netherlands) and P.N. Lebedev Physics Institute (Russia) [29][30][31].…”

“…The calculation method as well as the cross-section data for the interaction of electrons with CO2,Nz,He, Xe, and 02 are presented in [14, 15, 27J. In the case of a CO2 waveguide laser, the frequency of the rf field is generally much higher than the relaxation frequency of the upper laser level. So (30) contains values for q3 and q4 averaged in time over one period of the field. They can be connected with the pumping power W (t, x) and with the ~7 values in the following way:…”