Observation of power-dependent distortion of an infrared beam at 10.6 µm from a CO2laser during propagation in liquids

This paper reports the first experimental verification of the existence of the self-induced effect of spread and serious distortion of the infrared beam from the CO2laser system at 10.6 μm when propagating in various liquids. The power-dependent shape of the laser beam after passage through the liquid cell was visibly displayed on the Kalvar film by virtue of the thermal development method originally invented by our laboratory. The phenomenon observed is considered as having a thermal origin due to the partial absorption of the infrared beam; yielding localized heating, and thereby thermal convection which causes a complex change of the refractive index around the beam passing through the medium. The interference fringes found in the distorted beam pattern are likely attributed to the spherical aberration in the thermal defocusing lens induced in the material by the laser beam itself.