Shanghai Institute of Optics and Fine Mechanics has made progress in composite material based picosecond mirrors

Recently, the High Power Laser Element Technology and Engineering Department of the Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, has made progress in the research of composite based picosecond mirrors. The related research results were published in Optics and Laser Technology under the title of "Hybrid Material Based Mirror Coatings for Picosed Laser Applications".

Picosecond pulse lasers are often used for fundamental research in high-energy density physics. As a key component of picosecond laser systems, the laser damage threshold of mirrors directly affects the output energy of picosecond laser systems. Traditional picosecond laser mirrors use hafnium oxide and silicon oxide as high and low refractive index materials, respectively. In recent years, composite materials including nanostacks and mixtures have received widespread attention in improving the laser damage threshold of thin film components. The study of composite picosecond mirrors and their laser damage characteristics under different pulse widths of laser irradiation has certain practical application value.

Researchers have prepared four types of composite materials using electron beam evaporation technology, including hafnium oxide/aluminum oxide nanostack, hafnium oxide/silicon oxide nanostack, hafnium oxide aluminum oxide mixture, and hafnium oxide silicon oxide mixture. Compared with a single hafnium oxide material, composite materials can suppress crystallization and reduce surface roughness. Four types of reflective mirrors with working wavelengths at 1053 nm were prepared using the above-mentioned composite materials and silicon oxide materials as high and low refractive index materials. The damage test results of the mirror under different pulse widths (0.5 ps, 1 ps, 3 ps, and 8 ps) of laser irradiation show that compared with the picosecond mirror using hafnium oxide as the high refractive index material, the picosecond mirror using composite materials as the high refractive index material exhibits a higher laser damage threshold. Within the laser pulse range studied in this article, the initial laser damage mechanism of the reflector begins to change around 3 ps. This achievement is of great significance for improving the performance of optical thin film components such as picosecond laser reflectors.

Figure 1. AFM micrographs and RMS roughness of different mirrors, (b) laser-induced damage probability distribution (8 ps, 1053 nm)

Figure 2. Probability distribution of laser-induced damage with different pulse widths (a) 0.5 ps, (b) 1 ps, and (c) 3 ps; (d) The variation of laser damage threshold with laser pulse width

Note:
M-H refers to a picosecond mirror made of hafnium oxide, a high refractive index material;
M-N1 refers to a picosecond mirror with a high refractive index material of hafnium oxide/aluminum oxide nanostack;
M-N2 refers to a picosecond mirror with a high refractive index material of hafnium oxide/silicon oxide nanostack;
M-M1 refers to a picosecond mirror with a high refractive index material of hafnium oxide alumina mixture;
M-M2 refers to a picosecond mirror with a high refractive index material of hafnium oxide silicon oxide mixture.

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