The optical distortions of transmissive optics for high power CO2lasers have been measured by the interference of a probe He-Ne laser beam. The change of interference fringes is observed by a video camera when the sample is irradiated by a cw high power CO2laser. From the change of fringe pattern, the optical distortion is obtained and the spatial distribution of the temperature rise is derived. Thermal expansion and thermal change of the optics cause optical distortions. Both factors have to be added to large thermal lensing effects for ZnSe optics but they are small for KCI optics.
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