Research And Preparation Of Optical Coatings Used In Pulse CO₂ Laser

In high power TEA CO2 laser systems, optical coatings performance is a key technical problem which restricts the increase of the laser power and the laser beam quality. In this thesis,the design of full-reflect films, anti-reflect films and part-reflect films is studied theoretically and experimentally. This thesis also discussed the high power laser damage mechanism of optical coatings.This thesis studied materials thermal conductivity, absorbability and thermal expansion coefficient, selected adequate substrate materials of reflectors and windows. Using Needle optimizing designs, considering the inner electric-field intensity distribute in the coatings, this thesis designed coating structures with higher laser damage threshold and lower film thick sensitivity.A new combined monitoring method is introduced in this thesis for optical thin film thickness real time monitoring. This method, using the high accuracy of crystal oscillation monitoring method to adjust the turning points of optical monitoring, is more suitable for monitoring the deposition of IR optical coatings. Even when the crystal oscillation monitoring method is out of work, coatings are ensured by the optical overshoot turning point monitoring method.This thesis prepared some kinds of films used in TEA CO2 laser, including enhanced protecting reflect films, part-reflect GaAs laser window films and ZnSe anti-reflect films. They were all made by the ES-26CB evaporation equipment of the INNOTEC Company with IAD technique. Tested by the FT-IR spectrophotometer of Nicolet Company, all these films'performance meets the design parameters. They also showed good effect in real applications.This thesis analyzed the interplay mechanism of high power laser and optical coatings, computed the film temperature and stress distribution induced by pulsed laser, discussed the preparation factors which can affect optical coatings damage threshold. It is important for improving deposit factors and increasing optical coatings laser damage threshold.