Technological defects and operational conditions impact on the deformable mirrors operability

Аuthors

Shanin Y. I.

NII NPO "LUCH", Podolsk, Russia

e-mail: ShaninYuI@sialuch.ru

Abstract

The main optical element of the adaptive optical system is a deformable mirror, by which the aberrated wave front of laser radiation is corrected. Today, it is still possible to do with uncooled optical elements, both while creating pulsed high-power laser systems for inertial fusion, and continuous technological laser systems. This is allowed by the technology of applying multi-layer quarter-wave reflecting coatings on the optical surface, which ensures higher coefficient of specular reflection of the mirror reflecting surface, providing all at once their radiation resistance. Creating uncooled, deformable mirrors for pulsed and continuous laser systems is costly and time consuming. It is necessary to set reasonable requirements for the quality of the mirror optical surface processing for costs reduction. To this end, we have evaluated the critical sizes of possible defects of optical surface and coating on the mirror substrate at the manufacturing stage from the viewpoint of achieving limitations on temperature, strain, or displacement under laser loading conditions. The prepared optical surface may have trifle defects (stains, scratches), or there may be defects of the coating. It is important to know critical size of such defects, which exceeding may lead various damages of the mirror while operation up to the mirror failure. Ensuring the optical sur- face stability while mirror operation is the main task of both manufacturing process and during further operation of the mirror. The paper considers the effect of factors violating optical stability:

1) Temperature stability while the ambient temperature changes;

2) Thermal stability when optical surface is exposed to laser radiation, or heating of the mirror base due to the pulsed exposure to radiation from pumping lamps;

3) Due to the failure and warming up of the drives.

As the geometric stability of the mirror optical surface is a direct consequence of the thermal, physical and mechanical properties of the material of the mirror, the choice of the best materials for the mirrors is considered from the viewpoint of ensuring maximum stability parameters values. Silicon and silicon carbide are in the first place among non-metallic materials in all three parameters of stability (temperature, stress, displacement) when it comes to exposing uncooled optical elements to continuous laser radiation; copper (temperature) and molybdenum (stress, displacement) are the best among metals. Silicon carbide and copper (temperature), glassceramic CO-115M and superinvar (stress and displacement) are the best while exposing to pulsed radiation.

Keywords:

laser mirror, deformable mirror, optical element, powerful pulse laser system, laser system, temperature, heat flow.

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