Cryogenic high-power CO laser pumped by e-beam sustained discharge: theory and experiment

摘要

Cryogenic high-power CO lasers having an efficiency in the range of 30% have a good promise for many applications, including a material treatment (welding, cutting, hardening), selective chemistry and so on. Because of a shorter wavelength its radiation has a number of advantages over the CO: laser radiation. Among those are: the better focussability;less plasma shielding effect;availability of transparent materials withstanding a high-power density;reasonable optical fiber transmission. The disadvantage is the cryogenic gas temperature because of which the CO laser technology is less advanced in comparison with C02 lasers. CO lasers have rather high energy efficiency, however not so much is known about the optical quality of the high-power laser beam. Our experimental studies on the laser efficiency as a function of the input power , the gas composition. and gasdynamic conditions allows us to verify the kinetic model. This kinetic model was employed further for predictions of the laser beam quality for different optical cavity parameters, and energy loading in the gas flow. For this purpose 2 two-dimensional models were formulated: the first describes the self-consistent distributions of the multiwavelength wave field, gain, and index as functions of coordinates along the gas flow and along the cavity axis;the second describes the spatial distributions of the gain and index approximately as functions of the coordinates along the gas flow and along the discharge current Both models predict the strong influence of the refractive index non-uniformities on the beam quality, which may explain, in part, the experimentally observed poor beam quality. The methods to improve it will be discussed, including the phase conjugation in the active medium.