The research of picosecond laser mirror based on HfO2-Al2O3 mixed material has made progress in Shanghai Optical Machinery Institute

Recently, the Thin Film Optics Laboratory of the Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences and the Joint Laboratory of High Power Laser Physics have carried out cooperative research and made progress in the research of picosecond laser mirrors based on HfO2-Al2O3 hybrid materials. The research is published in the journal Optical Materials Express.

High power picosecond pulsed lasers are commonly used in basic research of high energy density physics, such as OMEGA EP, NIF ARC, SG-II-UP PW, etc. As a key component of picosecond laser system, the ability of picosecond laser reflector to withstand high intensity picosecond laser pulse is limited by the laser-induced damage threshold (LIDT). In recent years, optical thin film components based on hybrid materials have gained extensive attention for their superior performance over pure materials under nanosecond and femtosecond pulsed lasers. The hybrid material is expected to improve the performance of optical thin films under picosecond pulsed laser.

The researchers deposited a hybrid picosecond laser reflector (MPLM) by electron beam evaporation using HfO2-Al2O3 mixture and pure SiO2 material as high/low refractive index materials, respectively. For comparison, a traditional picosecond laser mirror (TPLM) was prepared by alternating deposition of pure HfO2 material and SiO2 material. The optical properties, microstructure and mechanical properties of MPLM and TPLM, as well as the LIDT (laser pulse width: 8 ps, laser wavelength: 1053 nm) and damage morphology under atmospheric and vacuum conditions were investigated. The results show that MPLM exhibits higher LIDT in both atmospheric and vacuum environments. The typical damage morphology shows that the laser induced damage of the two films is closely related to the electric field distribution, film defects and film stress. The finite element simulation results show that MPLM has a higher LIDT, which may be attributed to the mixing material reducing the temperature rise of the multilayer film under laser irradiation.

The relevant work has been supported by the National Natural Science Foundation of China and the Youth Innovation Promotion Association of the Chinese Academy of Sciences.

Figure 1. TPLM and MPLM: (a) elemental percentage distribution from low refractive index layer to high refractive index layer, (b) XRD pattern, (c) film stress aging behavior, (d) surface morphology

Figure 2. Laser damage probability of TPLM and MPLM: (a) atmospheric environment, (b) vacuum environment

Figure 3. Simulated temperature rise distributions of absorbent defects at the first, second, and third high electric field peaks in (a) TPLM and (b) MPLM

Source: Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences