“…The transition from the laser upper level (001) to the laser lower level (100) causes CO 2 laser oscillation in the 10.6 μm band, and the transition from the laser upper level (001) to the laser lower level (020) causes CO 2 laser oscillation in the 9.6 μm band. For example, small signal gain coefficients of CW CO 2 lasers with a direct current (DC) discharge and a longitudinal excitation scheme were reported to be about 1.1%/cm with a discharge volume of 754 cm 3 , a CO 2 /N 2 /He gas mixing ratio of 1:3:8, a gas pressure of 10.4 kPa and a discharge current of 90 mA, and 0.64%/cm with a discharge length of 210 cm, a CO 2 /N 2 /He gas mixing ratio of 1:5:30, a gas pressure of 6.5-6.9 kPa and an input power of 70 kW [15,16]. Small signal gain coefficients of short-pulse CO 2 lasers with a pulsed discharge and a transverse excitation scheme were reported to be 3.0%/cm with a discharge volume of 360 cm 3 , a CO 2 /N 2 /He gas mixing ratio of 1:1:3, a gas pressure of 66.7 kPa and an input energy of 36 J, and 2.9%/cm with an electrode length of 50 cm, a discharge gap of 5 cm, a CO 2 /N 2 /He gas mixing ratio of 3:1:16, a gas pressure of 97.3 kPa and an input power of 180 W, and about 2.5%/cm with a discharge volume of 1200 cm 3 , a CO 2 /N 2 /He gas mixing ratio of 2:1:12 and an input energy of 120 J [17][18][19].…”