Spectral beam combining technique is one of major approaches in power scaling of fiber lasers. In order to maximize beam-combining performance, maintain a high beam quality in the combining process, the absorption-induced wavefront distortion of the resulting combined beam must be considered. By reducing the film absorption, the dichroic filters will be promising competitors to dielectric gratings as crucial spectral beam combining elements. In this paper, two different structures: less-cavities (LC) structure and more-cavities (MC) structure of dichroic filter layers were carefully designed and fabricated by ion-beam sputtering deposition with high-precision layer thickness monitoring method. A photothermal scanning system based on laser-induced surface thermal lensing (STL) effect was used for analyzing the 1064nm wavelength absorption of dichroic filter layers in passband and stopband. Dichroic filter with reduced in-bandpass absorption was found in MC structure by relaxing the electric field strength in thin films. This approach is highly expected to have great potential for fabricating promising spectral beam combining dichroic filters with less thermal effect and higher laser-induced damage threshold (LIDT).
Laser damage threshold of optical components is an important indicator to measure the ability of components to resist laser damage. A low-absorption film is plated on the surface of the reaction sintered SiC substrate produced by ion beam sputtering method, and the fundamental frequency reflection efficiency is over 99.8%. A set of 1060 nm continuous laser damage threshold testing system has been established. After loading the SiC-based film sample with a continuous wave laser with a power density of 30 kW/cm2 for 30 s, it was found that the surface temperature rise of the SiC-based film was less than 2 K. the changes of temperature field and thermal stress on the surface of the SiC mirror when the continuous laser loading power and loading time by finite element method. The results are basically consistent with the experimental data. The experimental results verify that the thermal stress and thermal melting effect caused by high-power continuous laser loading are the mechanisms for the damage of mirrors, which provides an idea for improving the laser damage threshold of optical components.
Ta2O5/SiO2 mixed film is a very promising material for the preparation of new optical and optoelectronic devices, but there are few reports on its etching characteristics. In this paper, Ta2O5/SiO2 mixed films with various proportions of Ta2O5 were prepared by ion-beam sputtering deposition. CHF3-based reactive ion etching (RIE) was used to etch Ta2O5/SiO2 mixed films. The etching profiles of Ta2O5/SiO2 mixed films were observed by using a field-emission scanning electron microscope (SEM). The RIE etch rates were investigated as a function of the Ta2O5/SiO2 mixture ratio, RIE power, chamber pressure and etching gas ratio. It is found that the etch rate of Ta2O5/SiO2 mixed films increase with an increase of RIE power and chamber pressure, and decrease with an increase of Ta2O5 composition in the Ta2O5/SiO2 mixed films. Moreover, it is also found that as the proportion of F-based gas increases, the etching rate of the Ta2O5/SiO2 mixed film first increases and then saturates. These results would be of importance for the fabrication of optical and optoelectronic devices based on Ta2O5/SiO2 mixed films.
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