Subwavelength Quasi-Periodic Array for Infrared Antireflection

High-Transmission Biomimetics Structural Surfaces Produced via Ultrafast Laser Manufacturing

Inspired by periodically aligned micro/nanostructures on biological surfaces, researchers have been fabricating biomimetic structures with superior performance. As a promising and versatile tool, an ultrafast laser combined with other forms of processing technology has been utilized to manufacture functional structures, e.g., the biomimetic subwavelength structures to restrain the surface Fresnel reflectance. In this review paper, we interpret the biomimetic mechanism of antireflective subwavelength structures (ARSSs) for high-transmission windows. Recent advances in the fabrication of ARSSs with an ultrafast laser are summarized and introduced. The limitations and challenges of laser processing technology are discussed, and the future prospects for advancement are outlined, too.

Efficient fabrication of infrared antireflective microstructures on a curved Diamond-ZnS composite surface by using femtosecond Bessel-like beams

Antireflective microstructures fabricated using femtosecond laser possess wide-ranging applicability and high stability across different spectral bands. However, due to the limited aspect ratio of the focused light field, traditional femtosecond laser manufacturing faces challenges in efficiently fabricating antireflective microstructures with high aspect ratio and small period, which are essential for antireflection, on curved surfaces. In this study, we present a robust and efficient method for fabricating high-aspect-ratio and basal surface insensitive antireflective microstructures using a spatially shaped Bessel-like beam. Based on theoretical simulation, a redesigned telescopic system is proposed to flexibly equalize the intensity of the Bessel beam along its propagation direction, facilitating the fabrication of antireflective subwavelength structures on the entire convex lens. The fabricated microstructures, featuring a width of less than 2 µm and a depth of 1 µm, enhance transmittance from 75% to 85% on Diamond-ZnS composite material (D-ZnS) surfaces. Our approach enables the creation of high aspect ratio subwavelength structures with a z-position difference exceeding 600 µm. This practical, efficient, and cost-effective method is facilitated for producing antireflective surfaces on aero-optical components utilized in aviation.

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

Enhancing the infrared window transmittance of zinc sulfide (ZnS) is important to improve the performance of infrared detector systems. In this work, a new hybrid micro/nanostructure was fabricated by an optimal Bessel femtosecond laser on ZnS substrate. The surface morphologies and profiles of ASS ablated by a 20× microscope objective Bessel beam are described, indicating that the nanoripples on the micropore were formed by the SPP interference and the SPP scattering in a particular direction. Further, the maximum average transmittance of ASS increased by 9.7% and 12.3% in the wavelength ranges of 5~12 μm and 8~12 μm, respectively. Finally, the antireflective mechanism of the hybrid micro/nanostructure is explored using the novel electromagnetic field model based on the FDTD method, and we attribute the stable antireflective performance of ASS in broadband to the interface effective dielectric effect and LLFE.

Antireflection microstructures fabricated on the surface of a LiGaSe2 nonlinear crystal

LiGaSe₂ is a propitious material for nonlinear parametric conversion in the mid-infrared (mid-IR) range. Its refractive index of n = 2.25 in the 2-12 µm wavelength range results in significant losses due to Fresnel reflection. However, the conventional method of increasing the transmittance with antireflection coatings (ARCs) significantly reduces the damage threshold of the material. Fabrication of the antireflection microstructures (ARMs) is an alternative approach for increasing the surface transmittance. In this work, ARMs were fabricated on the surface of a LiGaSe₂ crystal using a single-pulse femtosecond laser ablation method. An average transmittance of 97.2% in the 2-8 µm spectral range and the maximum transmittance of 98.6% at 4.1 µm were achieved.