Plate laser beam splitter with mixture-based quarter-wave coating design

Plate laser beam splitter (PLBS) coatings for intensity-splitting in high-power laser applications face increasing requirements, where the challenge is to simultaneously satisfy a given transmittance (T)/reflectivity (R) intensity-splitting ratio with a certain bandwidth, and a high laser damage threshold (LIDT). Traditionally, a given T/R ratio is achieved by using a non-quarterwave design. We propose a quarter-wave design strategy for arbitrary T/R ratios by using mixture layers with tunable refractive index (n) and optical band gap as high-n layers. Two quarter-wave PLBS coatings based on Al2O3-HfO2 mixture with a designed T/R ratio of 50:50 are experimentally demonstrated and compared with the traditional PLBS coating. The mixture-based PLBS coating shows good spectral performance, low surface roughness, and high LIDT. For an s-polarized 8 ns pulse laser at a wavelength of 1064 nm, a mixture-based PLBS coating design can improve LIDT by a factor of ~2 with a slightly wider bandwidth. This tunable mixture-based PLBS coating design strategy provides support for the increasingly high output power of high-power laser systems.

用于高功率激光应用中光强分束的平板激光分束器（Plate Laser Beam Splitter, PLBS）涂层正面临日益严苛的性能要求，其核心挑战在于需同时满足特定带宽下的透射率（T）/反射率（R）分束比要求，以及极高的激光损伤阈值（Laser Induced Damage Threshold, LIDT）。传统上，特定的T/R分束比需通过非四分之一波长设计实现。本研究提出一种基于可调谐折射率（n）与光学带隙的混合层作为高折射率层的四分之一波长设计策略，可实现任意T/R分束比。我们通过基于氧化铝-二氧化铪（Al₂O₃-HfO₂）混合材料的方案，制备了两款设计光强分束比为50:50的四分之一波长PLBS涂层，并与传统PLBS涂层开展对比实验。该混合层基PLBS涂层展现出优异的光谱性能、较低的表面粗糙度以及较高的激光损伤阈值。针对波长1064 nm的s偏振8纳秒脉冲激光，该混合层基PLBS涂层可将激光损伤阈值提升约2倍，同时拥有略宽的带宽。这种可调谐混合层基PLBS涂层设计策略，为高功率激光系统不断提升的输出功率需求提供了技术支撑。