Similarity of laser window thermal effects

Abstract

We are concerned with the similarity and scaling law of the thermal effects of windows subjected to laser propagation and influences on laser beam quality. Using characteristic physical quantities and dimensionless equations, appropriate similarity relations are derived, independent of the specific properties of the materials and beams. As an example, a full-scale and a half-scale window are numerically analyzed to verify the relations. It is concluded that the phase aberration resulting from thermal deformation and thermo-optic effects comply completely with similarity-based scaling, while the phase aberration resulting from elasto-optic effects scales approximately. From the results of a model window, the performances of a full-scale window can be obtained using the similarity relations.

Analysis of thermo-optic effects in Nd:YAG ceramics disk under high heat load

“…The heat effects in HAPLS can be divided into two groups [8]: volume effects occurring during absorption of pump beam inside the gain medium (it is the subject of section 3), and thermo-optic effects occurring as a result of residual absorption on coating surfaces of passive elements like mirrors, windows, beam splitters, out-couplers etc [6,7] The latter ones cannot be neglected, because of several hundreds of Watts of heat power dissipated inside the optical element. To mitigate these effects the choice of substrate material is crucial (see Table 1).…”

“…However, because of specific application needs, the duration of operation has to be of few up to 50 s. Assuming output beam area from laser oscillator of few dozens of cm 2 (up to 100 cm 2 ) and typical absorption length of parts of cm, the heat volume is of 50 -100 cm 3 , and heat densities of 10 3 -4 W/cm 3 in a case of gain media. In a case of passive elements the incident pump densities can be of a few tens kW/cm 2 , which gives stringent requirements especially on out-couplers and dichroic mirrors [6,7]. To harness and mitigate the transient heat effects the large scale active optics systems operating at high laser power densities have to be deployed.…”

The investigation of transient thermal effects in optical elements under high laser intensities

“…Assuming output beam area from laser oscillator of few dozens of cm 2 (up to 100 cm 2 ) and typical absorption length of parts of cm, the heat volume is of 50÷100 cm 3 and heat densities of 10 3 ÷10 4 W/cm 3 in the case of gain media. In a case of passive elements the incident pump densities can be of a few tens of kW/cm 2 , what implies rigorous requirements especially on output couplers and dichroic mirrors [6,7]. To harness and mitigate the transient heat effects, the large scale active optics systems operating at high laser power densities have to be deployed.…”