Various forms of CO 2 lasers have achieved CW powers in the 60-kW range, operating efficiencies approaching 30 percent, pulse energies of approximately 2000 J, pulsewidths less than 1 ns, peak pulse powers in excess of 109W, a frequency stability of a few parts in 1012, and sealed-off tube lifetimes of many thousands of hours. In addition, the laser can be easily Q-switched as well as gain-switched and has been electrically, optically, gas-dynamically, and chemically pumped. In addition to all these attributes, the CO 2 laser output wavelength lies within one of the best atmospheric windows. It should be no surprise then that during the last eight years, the CO 2 laser has firmly established itself as a candidate for recognition as the most important among the numerous laser devices presently known. Depending on the gas pressure, gas flow rate, pumping mechanisms, gas mixture, etc., CO 2 lasers can exhibit a wide range of noise, bandwidth, gain, and power saturation characteristics. This flexibility enables a designer to optimize the performance of CO 2 laser stable-frequency master oscillators; power oscillators; low-noise high-gain preamplifiers; intermediate-power or high-power amplifiers. As a result, CO 2 laser oscillator-amplifier chains can be designed utilizing guidelines similar to those which have been extensively applied in the design of transmitters in the RF and microwave region of the electromagnetic spectrum.