Development of broadband high efficiency Mid-IR gratings for high-energy ultrafast lasers

Broadband high-efficiency diffraction gratings play a crucial role in the pulse stretcher and compressor of high-energy ultrafast lasers. Nevertheless, conventional grating manufacturing techniques, including mechanical ruling and holographic recording, face challenges in creating accurate blazed groove profiles necessary for the fabrication of broadband, high-efficiency midinfrared gratings. In this work, we utilized combined electron-beam lithography and anisotropic wet etching technology to fabricate nearly perfect blazed grooves, producing high efficiency broadband mid-infrared (IR) grating for 4.3 μm 100 femtosecond laser. Global optimization was performed to achieve a design of > 90% efficiency over spectral range of 3.6 μm - 6.6 μm. Hybrid metal-dielectric coating (Au-Al2O3) is employed and optimized to minimize absorption and to enhance diffraction efficiency and laser-induced damage threshold (LIDT). Prototype gratings undergo testing at a desired application wavelengths of 4.3 μm in a tunable range of 0.2 μm, revealing that the optimal sample achieves a diffraction efficiency of 92%, closely approaching the theoretical value of 94.2%.