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

Abstract

Mid‐infrared materials antireflection is in high demand for high‐powered or ultra‐broadband coherent light sources, where conventional antireflection coatings cannot be reliably applied. This work provides a critical review of the recent advances in microstructure fabrication technology for mid‐infrared antireflection applications. Several techniques are reviewed, including direct imprinting, wet and reactive ion etching using conventional photoresist masking, novel colloid crystal masks, and maskless etching, laser‐induced periodic structure formation, and multiple laser ablation method modifications, including femtosecond laser direct writing, direct laser interference ablation, and single pulse ablation. The advantages and drawbacks of the different approaches are discussed in detail to highlight the most promising techniques for the fabrication of antireflection microstructures capable of achieving 99% transmittance in the 2–16 μm range.

A heavily doped germanium pyramid array for tunable optical antireflection in the broadband mid-infrared range

“…This property leads to vast applications in MIR optical sensing and communications such as civilian and military purposes in tracking and positioning. 4 Most MIR transparent materials possess a high reflective index larger than 2. The surface made of materials with a high refractive index results in low transmittance due to the surface reflection loss associated with a refractive index ( n e ).…”

Substrate-Independent Maskless Writing of Functionalized Microstructures Using CHic Chemistry and Digital Light Processing

“…With photocurable resins, the fabrication of microstructures has increasingly attracted interest in both academia and industry. Over the past decades, significant efforts have been made in developing maskless technologies to fabricate microstructures at significantly reduced costs and increased flexibility. , Among them, one of the most promising maskless technologies is photolithography based on digital light processing (DLP). − DLP is a projection technology using a so-called digital micromirror device (DMD) as a spatial light modulator invented by Texas Instruments in 1987 . DMDs consist of an array of several hundred thousand microscopic mirrors which can be rotated in such a way that the light is either directed to a substrate or (in the dark mode) to a light dump.…”

“…Over the past decades, significant efforts have been made in developing maskless technologies to fabricate microstructures at significantly reduced costs and increased flexibility. 2 , 3 Among them, one of the most promising maskless technologies is photolithography based on digital light processing (DLP). 4 − 6 DLP is a projection technology using a so-called digital micromirror device (DMD) as a spatial light modulator invented by Texas Instruments in 1987.…”

CO and CO2 laser beam guiding with silver halide polycrystalline fibers and hollow waveguides

“…The industrial and medical applications of these lasers can be essentially extended by means of flexible fiber-optic cables that transmit the laser power to desired locations. There are plenty of infrared materials transparent in the spectral range from 2 to 18 µm, but only a few of them can be used for the manufacturing of uniform long-length IR fibers with acceptable optical and mechanical properties [2,3]. For the mid-infrared spectral range various fibers are commercially available: chalcogenide, polycrystalline silver halide and hollow-core fibers.…”