Ultrabroadband suppression of mid-infrared reflection losses of a layered semiconductor by nanopatterning with a focused ion beam

Abstract

Moth-eye structures are patterned onto gallium selenide surfaces with sub-micrometer precision. In this way, Fresnel reflection losses are suppressed to below one percent within an ultrabroad optical bandwidth from 15 to 65 THz. We tune the geometry by rigorous coupled-wave analysis. Subsequently, ablation with a Ga+ ion beam serves to write optimized structures in areas covering 30 by 30 μm. The benefits are demonstrated via optical rectification of femtosecond laser pulses under tight focusing, resulting in emission of phase-stable transients in the mid-infrared. We analyze the performance of antireflection coating directly in the time domain by ultrabroadband electro-optic sampling.

Detection Efficiency and Bandwidth Optimized Electro-Optic Sampling of Mid-Infrared Waves

“…Up to now, anti-reflection coating of GaSe was demonstrated in [151] for 800-nm wavelength with magnetron sputtering of SiO 2 and SiO 2 /Si 3 N 4 layers, leading to a higher THz generation efficiency, as less driving pulse power is reflected off the front surface. Furthermore, [152,153] show that the fabrication of anti-reflection micro-structures can be used to increase the MIR transmission of GaSe crystals. However, the effect of the microstructures on the crystal damage threshold still has to be investigated.…”

Optical Absorption, Photocarrier Recombination Dynamics and Terahertz Dielectric Properties of Electron-Irradiated GaSe Crystals

“…The high reflection coefficient for the near-IR radiation and limited applicability of standard methods and materials to produce the antireflection coatings (AR) also limit the efficiency of the applications of this material. Nevertheless, there are examples of ARs for GaSe crystals developed during the last five years [22,23].…”