Gain characteristics of CO2laser amplifiers at 10.6 microns

Single-pass gain at 10.6 microns has been studied parametrically in nonflowing CO2or buffered CO2amplifying media. The gain profile across the amplifier diameter and integrated gain both were determined. Parameters varied included buffer gas type, mixture ratio, gas pressure, amplifier bore, discharge current, and wall temperature. Tube bores of 12, 22, and 34 mm and buffer gases of H2, He, Ne, A, and N2were studied. Optimum gain is relatively independent of current density, but decreases with increasing wall temperature. The pressure-diameter relationshipP_{CO_{2}} cdot D sim 4torr-cm was found to hold for CO2, CO2:He, and CO2:N2amplifying media at optimum gain. The gain depends strongly on the CO2partial pressure and is relatively insensitive to the buffer gas pressure except for the case of H2. The maximum gain decreased slowly with increasing amplifier diameter. The highest gain, 1.7 dB/meter, was achieved with a helium buffer gas in amplifiers with a diameter of 22 mm or less. No gain saturation was detected for a 30-dB range of input signal power, from a milliwatt to a few watts. Spectrograms showed that the principal spontaneous emission from CO2:He amplifiers in the 2000-7000-Å range consisted of CO bands; no CO2bands or He line spectra were observed.