Fabrication of an Anti-Reflective Microstructure on ZnS by Femtosecond Laser Bessel Beams

Abstract

As an important mid-infrared to far-infrared optical window, ZnS is extremely important to improve spectral transmission performance, especially in the military field. However, on account of the Fresnel reflection at the interface between the air and the high-strength substrate, surface optical loss occurs in the ZnS optical window. In this study, the concave antireflective sub-wavelength structures (ASS) on ZnS have been experimentally investigated to obtain high transmittance in the far-infrared spectral range from 6 μm to 10 μm. We proposed a simple method to fabricate microhole array ASS by femtosecond Bessel beam, which further increased the depth of the microholes and suppressed the thermal effects effectively, including the crack and recast layer of the microhole. The influence of different Gaussian and Bessel beam parameters on the microhole morphology were explored, and three ASS structures with different periods were prepared by the optimized Bessel parameters. Ultimately, the average transmittance of the sample with the ASS microhole array period of 2.6 μm increased by 4.1% in the 6 μm to 10 μm waveband, and the transmittance was increased by 5.7% at wavelength of 7.2 μm.

Carbon Nanotubes Use for the Semiconductors ZnSe and ZnS Material Surface Modification via the Laser-Oriented Deposition Technique

“…schemes as well, and they can dramatically extend the applications of optoelectronics devices [1][2][3][4]. ZnSe and ZnS materials can be considered as perspective semiconductors to form the different detectors for the wide spectral range and to develop the mirrors and the optical limiting instruments [5][6][7][8][9][10][11][12][13][14][15][16][17]. Researchers have revealed the anti-reflective, luminescent properties of these materials and visualized the process of the nanoparticles' creation based on the ZnSe and ZnS structures and their introduction into the polymer matrices [8][9][10][11].…”

“…Researchers have revealed the anti-reflective, luminescent properties of these materials and visualized the process of the nanoparticles' creation based on the ZnSe and ZnS structures and their introduction into the polymer matrices [8][9][10][11]. Treatment of these materials by femtosecond lasers has been explained as well [12,16].…”

Broadband Antireflective Hybrid Micro/Nanostructure on Zinc Sulfide Fabricated by Optimal Bessel Femtosecond Laser

“…Zero-order Bessel beams have a decisive advantage over Gaussian beams [ 36 ] in creating deeper micropores [ 33 ]. In particular, explained from the characteristics of penetration geometry and nonlinear robustness, there are obvious differences in ASS on the ZnS surface fabricated by a Bessel beam with various light field distributions [ 37 , 38 ].…”

“…The laser fluence of the zero-order and the first-order diffraction rings of the Bessel beam was 9.9 J/cm 2 and 0.39 J/cm 2 with a pulse energy of 1.8 μJ, respectively. Since the accumulated energy of multiple pulses was still higher than the ablation threshold of 0.48 J/cm 2 [ 33 ], the molten material in the cavity was sprayed, adhered to, deposited, and then cooled to the edge of the hole, forming the recast layer during the laser ablation, as depicted in Figure 1 a–c. The morphology of the microstructure gradually evolved into a clear micropore as the pulse number decreased from 1 × 10 6 to 1 × 10 4 for the pulse energy of 2 µJ, while the volcanic structure was still formed by the molten material sticking to the edge of the hole, as demonstrated in Figure 1 d–f.…”

“…Zhang et al designed and fabricated an antireflective structure by a femtosecond laser-shaped beam on ZnS, resulting in transmittance enhancement in the 5.5–14 μm wavelength range, expressing broadband response and a large acceptance angle [ 31 ]. Several research teams [ 4 , 32 , 33 ] have agreed that the depth of ASS is a key factor to improve the antireflective performance, since it determines the smoothness of an effective refractive index gradient. However, the depth of ASS processed by the Gaussian beam with a small focal depth and concentrated energy is insufficient, which suppress the transmittance within the infrared band [ 34 ].…”