Abstract
We have established a thermal distribution model of the multilayer dielectric grating with laser irradiation based on the Beer–Lambert theory and the thermal conduction theory. The temperature change on the surface and inside of the grating is simulated according to the laser irradiation time, laser power, substrate size, and substrate material. The actual thermal behavior of a 50 × 50 × 10 mm3 multilayer dielectric grating with fused silica substrate is measured with 10 kW fiber laser irradiation. The results show a dynamic equilibrium between the energy absorbed in the laser irradiation area and the energy transferred in the thermal transfer area when the maximum temperature of the grating is kept stable. The simulation results are in good agreement with the experimental data, which provides a reference for understanding the thermal dynamics process of the multilayer dielectric grating with high power density laser irradiation.
Highlights
We found a dynamic equilibrium between the energy absorbed in the laser irradiation area and the energy transferred in the thermal transfer area when the maximum temperature of the Multilayer dielectric (MLD) grating is kept stable
The experimental results show a dynamic equilibrium between the energy absorbed in the laser irradiation area and the energy transferred in the thermal transfer area when the maximum temperature of the MLD grating remains stable
We established a thermal distribution model of the multilayer dielectric grating with laser irradiation based on the Beer–Lambert theory and the thermal conduction theory
Summary
Multilayer dielectric (MLD) grating has great applications in many fields, such as laser pulse compression broadening, beam splitting, beam dispersion, and chirped-pulse compression. MLD grating is a critical device in combining laser beams into a single beam in a spectral beam combination (SBC) system. SBC is a laser incoherent combination method, which combines laser beams with different wavelengths into a single beam. SBC has an advantage of single aperture output and low requirement in the beamlet phase, which becomes the most promising scheme among the beam combining technologies. In 2016, Ye Zheng reported a 10.8 kW polarization independent MLD grating spectral beam combining with a diffractive efficiency of 94%.13 Usually, the MLD grating experienced a high-level power exposure in an SBC system. With the increase of the irradiation laser power, the temperature of the MLD grating will increase, leading to surface thermal distortion of the MLD grating. MLD grating is a critical device in combining laser beams into a single beam in a spectral beam combination (SBC) system.. The MLD grating experienced a high-level power exposure in an SBC system.. Thermal deformation of the MLD grating surface takes place for the application of SBC, which may lead to a great degradation of the combined beam quality.. It is necessary to consider the temperature variation of the MLD grating with high power density laser irradiation.. The proposed model does not coincide with the actual situation of the laser beam irradiation on the translucent medium, and the temperature change of the MLD grating under thermal equilibrium was not analyzed. The simulated and experimental results reveal approaches to reduce the temperature of the MLD grating under high power laser irradiation. This work enriches the understanding of the temperature rise mechanism of the MLD grating under high power laser irradiation
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