Self-heterodyne detection of backscattered radiation in single-mode CO2 lasers

Self-heterodyning in dc-discharge-pumped single-mode CO2 lasers is analysed theoretically and studied experimentally under strong and weak feedback conditions. Relations for the autodyne gain and modulation depth due to the effect of backscattered radiation with a Doppler-shifted frequency are obtained. Nonlinear distortions of the autodyne signal caused by a strong laser-target feedback are studied. It is shown that the autodyne detection of backscattered radiation in CO2 lasers can be considered linear even in the case of strong laser beam distortions (nonlinear distortions below 5%).