Fabrication of anti-reflective microstructures on chalcogenide crystals by femtosecond laser ablation

Review of Surface Modification Technologies for Mid‐Infrared Antireflection Microstructures Fabrication

“…To prove the statements above, we numerically calculated the dependence of ARM transmittance on depth using the finite element method in our previous work. [ 51 ] Here, we provide more results of a similar calculation of ARM transmittance dependence on four morphological characteristics (shown in Figure 3). If the aspect ratio of ARM is more than 1.5, more than 98% transmittance of light can be reliably achieved (see Figure 3a).…”

“…This result is in accordance with the other research of the same phenomena [ 34,39 ] and was proved with experimental measurements conducted in ref. [51]. Further increase in depth will lead to an increase in average transmittance across mid‐IR spectral range, which is crucial for broadband AR in the mid‐IR.…”

“…In ref. [51], ARMs were fabricated using Yb:KGW with wavelengths of fundamental (1026 nm) and second (513 nm) harmonics. A pulse duration of 200 fs was focused onto the sample surface with 100 × objective lenses.…”

“…Although the aspect ratio was about 1.5 and the control of the cross‐section profile was barely possible, this setup provides a throughput of several centimeters per hour. Using the described setup, ARMs of decent quality (see Figure a) were fabricated on binary cadmium selenide‐sulfide compound (CdSSe) sample with approximately 99% per‐surface transmittance in the 5–6 m range, while the average transmittance was 97% in the 2.5–10 m range [ 51 ] (see Figure a). This method was also utilized for the treatment of ZnSe [ 127 ] to achieve an average transmittance higher than 95% in the 4–10 m range and a maximum of 97% in the 6–8 m range (see Figure 17b).…”

“…Adapted with permission. [ 51 ] Copyright 2019, The Optical Society. Direct laser writing on sapphire substrate (b).…”