Thermal methods for cooled laser mirrors testing


Аuthors

Shanin Y. I.

NII NPO "LUCH", Podolsk, Russia

e-mail: ShaninYuI@sialuch.ru

Abstract

The stress-strain state of the laser mirrors is determined by the temperature distribution in them. In steady state operation, the temperature field in the mirror determines the intensity distribution in the laser beam, the design and material of the mirror, and the heat exchange characteristics of the cooling system. The non-stationary field of temperature in the mirror is characteristic of the moments of the beginning and the end of influence of laser loading. Test of mirrors under the influence of regular laser loading is very expensive and labor-consuming action. The paper proposes two methods of simulation testing of mirrors that do not require laser loading. The proposed thermal test methods are based on the practical adequacy of the mathematical formulation of the problem of loading a mirror with a heat flux from laser radiation and a flux due to the temperature difference between the coolant and the mirror design. The methods are based on the comparison and equalization of temperature moments that occur during different thermal loads. For thermal loading “thermal shock” and linear heating of the coolant are used. In the case of thermal shock at the initial moment of time the coolant with a constant flow rate and temperature different from the mirror temperature is fed into the mirror. The linearly increasing temperature of the coolant is also used as a thermal test method. Application of these methods is effective that thickness of a mirror basis is many times more than thickness of a substrate with an optical surface. In this case, the magnitude of thermal disturbances from the coolant may be insignificant, and the result from their effect is equivalent to the effects of heat fluxes from a laser load in excess of 107 W/m2. The paper presents analytical solutions for one-dimensional temperature fields, which allowed to establish the relationship between the possible heat fluxes from the laser load and the parameters of thermal loads – flow rate, temperature difference between the coolant and the design, heating rate of the coolant. The effectiveness of the proposed thermal methods was experimentally shown by the example of technological mirrors.

Keywords:

laser mirror, cooling system, temperature distribution, heat transfer, thermal shock, temperature bending moment

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