High-Transmission Biomimetics Structural Surfaces Produced via Ultrafast Laser Manufacturing

Abstract

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.

Keywords: antireflective surfaces; biomimetic structures; high transmission; ultrafast laser manufacturing.

Figure 1

(a) Moth eyes; (b) scanning electron microscopy (SEM) image of the details of ommatidia; (c) flat substrate; (d) one-dimensional grating surface; (e) multilevel surface profile; (f) continuous conical surface profile; (g) continuous parabolic conical surface profile. (a,b) Reproduced from Sun et al. [65] and Müller et al. [48], with permission from Springer Nature and MDPI, respectively.

Figure 2

(a) Top view and (b) cross-section profile of the designed antireflective subwavelength structures (ARSSs); (c) Contour plot of transmittance as a function of period p and incident wavelength measured via rigorous coupled-wave analysis (RCWA); (d) corresponding simulated period-dependent transmittance spectra; (e) contour plot of transmittance as a function of height h and incident wavelength measured using RCWA; (f) corresponding simulated height-dependent transmittance spectra. Reprinted from Wang et al. [68], Copyright 2023, with permission from Elsevier.

Figure 3

(a) absorption spectrum of zinc sulfide (ZnS) ranging from 200 to 500 nm; (b) gratings of period with 1μm; periodic square arrangement pillars of (c) 1 μm, (d) 2 μm, (e) 3 μm and (f) 4 μm. The scale bar for (a–f) represents 5 μm. Reprinted with permission from [72] © The Optical Society.

Figure 4

(a) Transmittance of single- and double-sided zinc sulfide (ZnS); (b) transmittance of double-sided ZnS with varying pillar depths; (c) transmittance of double-sided ZnS with varying periods; (d) transmittance of band double-sided ZnS at incident angles ranging from 0° to 40°. Reprinted with permission from [72] © The Optical Society.

Figure 5

(a) Scanning electron microscopy (SEM) image of antireflective subwavelength structures (ARSSs) on sapphire without etching; (b) SEM image of ARSS on sapphire after etching; (c) measured transmittance of fabricated ARSS on sapphire with and without etching. Reprinted with permission from [77] © The Optical Society.

Figure 6

(a) The experimental setup for parallel femtosecond laser fabrication. MLA, microlens array; OL, objective lens; D, distance between MLA and OL; Sample, ZnS; (b) photograph of an ARSS sample fabricated using parallel femtosecond laser; (c) typical optical field intensity distribution of 5 × 5 foci diffraction pattern. Adapted from Zhang et al. [82], Copyright 2018, with permission from OSA Publishing.

Figure 7

SEM images of microstructures were captured at different laser repetition rates: (a) 167 Hz, (b) 200 Hz, (c) 250 Hz. The morphologies of the microstructures were further analyzed with varying incident laser polarizations, as shown in (d,f). Laser polarization directions are indicated by yellow arrows; (g) duty ratio of the nanogratings’ area in the entire micrograting region under different laser energies. The inset is the SEM image of the fabricated surface corresponding to the laser energy; (h) simulated nanograting period versus excitation of electron. The inset is the SEM image of the typical nanograting. The scale bars in (a–f,h) represent 5 μm and 400 nm, respectively. Adapted from Zhang et al. [82], Copyright 2018, with permission from OSA Publishing.

Figure 8

(a) Transmittance spectra of the flat zinc sulfide (ZnS) and antireflective subwavelength structures (ARSSs) were tested (exp) and simulated (sim); (b) transmittance spectra of the fabricated ARSS were examined after undergoing different circle-of-abrasion tests; (c) transmittance spectra of ARSS fabricated with different laser powers of 50 mW, 60 mW and 70 mW; (d) transmittance spectra of the ARSS were studied with different orientation angles β between the nanogratings and microgratings. The scanning electron microscopy (SEM) image inset displays the ARSS with an angle of β = 60°. The incident angle θ-dependent measured transmittance spectra of ZnS with a one-sided (e) or double-sided (f) ARSS. Adapted from Zhang et al. [82], Copyright 2018, with permission from OSA Publishing.

Figure 9

(a) Schematic illustration of the fabrication procedure of a sapphire surface with antireflective subwavelength structures (ARSSs); (b–d) SEM images of ARSS on sapphire; (e) three-dimensional (3D) morphology and (f) cross-section profile of the biomimetic sapphire surface with ARSS. Adapted from Liu et al. [89]. Copyright © 2022 Springer Nature.

Figure 10

(a) Experimentally measured and (b) theoretically simulated transmittance of sapphire with antireflective subwavelength structures (ARSSs) on one side and both sides; (c) transmittance of the biomimetic sapphire surface with ARSS on both sides concerning incident angle; (d) relationship between transmittance of the ARSS and the incident angle at a fixed wavelength of 4 μm; (e) schematic illustration for the measurement and simulation of transmittance with different incident angles; (f) theoretically simulated transmittance and reflectance of the ARSS on both sides regarding the incident angle, with a fixed wavelength of 4 μm. Copyright © 2022 Springer Nature [89].

Figure 11

(a–d) Photograph of a Cicada Cretensis wing and scanning electron microscopy (SEM) images (45° tilted) at different magnifications showing the transparent antireflective area, with the red spot indicating the SEM imaging area; (e–h) photograph of a fused silica plate and SEM images (45° tilted) showing a spot fabricated on the surface, with the red spot indicating the location of irradiation; (i) period of nanospikes as a function of pulses number of NP; (j) period of nanospikes as a function of fluence at number of pulses NP = 10; (k) SEM images (45° tilted) of a single nanospike; (l) radius of nanospikes as a function of NP for fixed fluence (FI) = 6.6 J/cm²; (m) radius of nanospikes as a function of fluence for NP = 10; (n) cross-section SEM image of the femtosecond-laser-induced nanospikes; (o) height distribution. Reprinted from Antonis et al. [95], Copyright 2019, with permission from Wiley.

Figure 12

Antireflection measurement (a) A photograph of a fused silica sample plate, with the central part being subjected to laser treatment to create nanospikes. The reflectance of the flat and laser-treated areas on one or both sides of the fused silica plate is shown in (b,c). Reprinted from Antonis et al. [42], Copyright 2019, with permission from Wiley.

Figure 13

Applications of ARSS in some fields. (a) ARSS produced by femtosecond laser on ZnS. (b) Photography of the encapsulated PV module. (c) Photography of flat ZnS and laser-treat ZnS for infrared detection. (d) Transparent antireflection surface with high contact angle, with images of three liquid droplets: water (bottom middle), oleic acid (bottom left), and hexadecane (bottom right). (e) Water droplets on a transparent surface with ARSS and on flat glass. The very low reflectance and high water contact angle of the surface with ARSS contrast intense reflection and low water contact angle on flat glass. (a) Adapted from Wang et al. [71], with permission from MDPI; (b) adapted from Luo et al. [100], with permission from Elsevier; (c) adapted from Wang et al. [70], with permission from Elsevier; (d) adapted from Mazumder et al. [101], with permission from RightsLink; (e) adapted from Kyoo-Chul et al. [13], with permission from Rightslink. All rights reserved.