THERMAL DEFOCUSING OF CO2 LASER RADIATION IN GASES

The steady-state thermal defocusing of CO2 laser radiation (10.6-µ wavelength) in gases has been investigated experimentally and theoretically. The increase in the beam diameter and change in intensity caused by the self-induced index of refraction variations in absorbing gases has been studied as a function of laser beam power, the absorption coefficient of the gas, and the absorption pathlength. A Mach-Zehnder interferometer was used to examine directly the changes in the index of refraction of the absorbing gas, which cause the thermal defocusing. The experimental results compare favorably with a perturbation solution of thermal defocusing, taking into account the effects of thermal conduction and natural convection. Copyright © 1969 by The Institute of Electrical and Electronics Engineers, Inc.