Gain characteristics of CO2laser amplifiers at 10.6 microns

Single-pass gain at 10.6 microns has been studied parametrically in nonflowing CO
2
or buffered CO
2
amplifying 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 H
2
, He, Ne, A, and N
2
were studied. Optimum gain is relatively independent of current density, but decreases with increasing wall temperature. The pressure-diameter relationship
P_{CO_{2}} \cdot D \sim 4
torr-cm was found to hold for CO
2
, CO
2
:He, and CO
2
:N
2
amplifying media at optimum gain. The gain depends strongly on the CO
2
partial pressure and is relatively insensitive to the buffer gas pressure except for the case of H
2
. 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 CO
2
:He amplifiers in the 2000-7000-Å range consisted of CO bands; no CO
2
bands or He line spectra were observed.