Investigations of transient thermal optics effects in 10kW fiber laser effector

Abstract

The performance of laser weapon system depends among others on harnessing or mitigation of transient thermal optics effects (trans-TOE’s) occurring inside High Energy Laser (HEL) and in laser optics beam forming train as well. In the developed in last year at MUT laser effector based on of 10-kW fiber HEL the optical train consists of about ten lenses, mirrors and windows including the most critical fiber endcap. We have measured the transient 2D temperature distributions in these optical elements under 10-kW laser beam exposition and compared results to numerical modeling in COMSOL Multiphysics. Applying such experimental / numerical approach the effective absorption in dielectric layers of typical mirrors and in volume of transmissive elements under high laser power were determined. The layer absorption was determined to 20 − 50 ppm for High Reflective (HR) mirrors and less than 10 ppm for Anti Reflecting (AR) coatings. The idea of dynamic self-compensation of trans-TOE’s by means of tailored design of the following transmissive and reflecting elements was proposed. The numerical model of this concept for the simplest combination consisted of 2 HR mirrors and single AR coated lens was presented.