Figure - available from: Advanced Optical Materials
This content is subject to copyright. Terms and conditions apply.
Metasurface fabricated for the design point of 0% sloping using the mask displayed in Figure 3c. Panels (a) and (b) show the MS under angled viewing and in cross‐section, respectively, while the predicted reflectance contours as a function of feature height and fill factor are shown in (c). The location marked with the yellow “x” in (c) denotes this fabricated MS.
Source publication
Optic processing advances have shifted system limitations, with current constraints consisting of antireflective (AR) coatings applied to optics and the inability to reduce size, weight, and price. Metasurfaces, and more broadly metaoptics, provide an avenue to overcome these limitations. The ability to generate substrate‐engraved metasurfaces that...
Similar publications
The contact interface between the stator and the rotor tip of the spindle could be destructed when the spindle is rotating continually at high speed, which will cause strong noise and severe vibration. In order to reduce the sound pressure level of the noise generated by the rotating spindle, three different coating materials, that is, Al-Ti-Cr-C,...
The microstructure and composition of micro-arc oxidation (MAO) Zn-Si-containing calcium phosphate (Zn-Si-CaP) coatings deposited at different values of the applied voltages were investigated. It was shown that the increase of the anodic voltage from 150 to 350 V led to the linear increase of the coating’s thickness, surface roughness, surface and...
This piece of work deals with the influence assessment of the kind of coating of the cutting inserts and their wear on the dimensional accuracy and the top layer microstructure and roughness of the surface machined with constant cutting parameters vc = 85 m/min, f = 0.14 mm/obr and ap = 0.2 mm. The tests were performed on shafts made of Inconel 718...
Citations
... This latter, bio-inspired approach [16,[50][51][52][53] has become more popular in recent years thanks to its good performances and to the progress in micro-and nano-fabrication. 3D structures can be obtained via top-down lithography [16,48,51,[54][55][56][57][58][59][60][61][62][63][64][65], colloidal self-assembly assisted lithography [56,66,67], nano-imprint lithography of polymers [45,46,49,51] and of metal oxides [42][43][44]68]. ...
... For these reasons, the use of ARCs based on adiabatic index matching is nowadays a wellestablished strategy that extends the usable power range of pulsed and CW lasers. These 3D structures are built with a material having a refractive index close to that of the substrate [43,68] or are directly engraved in the substrate itself [16,37,39,57,59,[61][62][63][64][65][66][67]. The 3D features of the ARCs have relatively large vertical aspect ratio (height over lateral size h/d⪆1) a height close or larger than the wavelength of the incident light (h⪆λ), high density (⪆10/λ 2 ) and can be either ordered or disordered. ...
... This kind of ARCs can be tailored to have high transmission and handle high-power lasers: they reduce the impact of the incident light by confining the field intensity in the air gaps between the 3D dielectric elements [73][74][75]. Recent reports of this approach showcased outstanding performances providing LIDT very close to that of the underlying fused silica (FS) substrate (30 J/cm 2 at 351nm with 8 ns pulses, 74 J/cm 2 at 1053 nm with 4 ns pulses), and reflectance below 1% from 400 to 1100 nm [62][63][64][65]. ...
We demonstrate efficient anti reflection coatings based on adiabatic index matching obtained via nano-imprint lithography. They exhibit high total transmission, achromaticity (99.5% < T < 99.8% from 390 to 900 nm and 99% < T < 99.5% from 800 to 1600 nm) and wide angular acceptance (T > 99% up to 50 degrees). Our devices show high laser-induced damage thresholds in the sub-picosecond (>5 J/cm ² at 1030 nm, 500 fs), nanosecond (>150 J/cm ² at 1064 nm, 12 ns and >100 J/cm ² at 532 nm, 12 ns) regimes, and low absorption in the CW regime (<1.3 ppm at 1080 nm), close to those of the fused silica substrate.
... These set of requirements for large aperture size scalability and laser power-energy durability and the challenges described to the more typical "shape-sensitive" MS are addressed with the "averaged-index" MS approach we have developed [2][3][4][5][6][7][8][9][10][11][12][13][14], as will be describe next. However, for these "averaged index" MS to become a viable solution there were different obstacles and challenges that had to be overcome first, such as substantial increase in the MS layer thickness. ...
... The increase in particle height could enable and increase in the MS depth, and the increase in FF could typically further assist in achieving lower reflectivity. Utilizing the technique of "seeded dewetting" we have been able to enhance the bandwidth of the AR based on the baseline process [10]. In fig 5a, ARMS using "seeded dewetting" and Au NP as etch mask result in AR that is comparable and even shows improvement over commercial broadband MLD coatings. ...
... Broadband anti-reflective (AR) MS demonstration: (a) broadband ARMS: spectral transmission (blue) compared to comercially available multilayer dielectric broadband AR (black, red), and SEM of the ARMS and image of the sample[10]. (b) ultrabandwidth ARMS: spectral transmission (blue) compared to the broadband ARMS from (a) (black) and reference window (magenta), and SEM of the ARMS and image of the double sided AR 2-inch round sample[12]. ...
... The requirement for large-aperture optics and nanoscale feature spacing brings the focus to rAR technologies; within this subcategory, there are two common approaches: an in situ maskless approach, and an etching mask approach. The latter etching mask approach enables additional control over the Research Article nanoscale MS feature size, spacing, and shape, and consequently is the fabrication method of choice for this work [18][19][20][21]. In addition to AR technologies, this mask-based technology has recently been used to demonstrate optics element patterning and birefringence from a nonbirefringent material [22,23]. ...
... The etched structure is depicted in the electron micrograph in Fig. 1. Dewetting of gold on fused silica, in addition to the MS fabrication process discussed here, has been well documented elsewhere [18,19,[29][30][31][32]. After etching, semiconductor-grade gold etchant is used to remove any residual metal, resulting in the all-glass metasurface. ...
... The MS portrayed in Fig. 1 corresponds to the red 'x' on the contour plot in Fig. 2. Experimental reflectance measurements of this sample at 351-nm incident light yielded 0.37% R, agreeing very well with the model's predicted reflectance of 0.41%. The agreement between the model and fabricated structures has been reported multiple times before, so we encourage the readers to refer to those publications for more details [18][19][20][21]. Reflectance contour plot from a metasurface with feature sidewalls that are 65% sloped. ...
To fabricate optical components with surface layers compatible with high-power laser applications that may operate as antireflective coatings, polarization rotators, or harness physical anisotropy for other uses, metasurfaces are becoming an appealing candidate. In this study, large-beam (1.05 cm diameter) 351-nm laser-induced damage testing was performed on an all-glass metasurface structure composed of cone-like features with a subwavelength spacing of adjacent features. These structures were fabricated on untreated fused silica glass and damage tested, as were structures that were fabricated on fused silica glass that experienced a preliminary etching process to remove the surface Beilby layer that is characteristic of polished fused silica. The laser-induced damage onset for structures on untreated fused silica glass was ${19.3}\;{{\rm J}\cdot {\rm cm}^{- 2}}$ 19.3 J ⋅ c m − 2 , while the sample that saw an initial pretreatment etch exhibited an improved damage onset of ${20.4}\;{{\rm J}\cdot {\rm cm}^{- 2}}$ 20.4 J ⋅ c m − 2 , only 6% short of the reference pretreated glass damage onset of ${21.7}\;{{\rm J}\cdot {\rm cm}^{- 2}}$ 21.7 J ⋅ c m − 2 . For perspective, the National Ignition Facility operational average fluence at this wavelength and pulse length is about ${10}\;{{\rm J/cm}^2}$ 10 J / c m 2 . At a fluence of ${25.5}\;{{\rm J}\cdot {\rm cm}^{- 2}}$ 25.5 J ⋅ c m − 2 , the reference (pretreated) fused silica initiated 5.2 damage sites per ${{\rm mm}^2}$ m m 2 , while the antireflective metasurface sample with a preliminary etching process treatment initiated 9.8 damage sites per ${{\rm mm}^2}$ m m 2 . These findings demonstrate that substrate-engraved metasurfaces are compatible with high energy and power laser applications, further broadening their application space.
... Two substrate-engraving techniques based on directional dry etch that have demonstrated potential for scaling up to meter-length scale optics apertures while maintaining few tens of nanometers period scale are: (1) ion bombardment or the creation of in situ nucleation sites, [26][27][28] and (2) etching masks to guide the etching process. [29][30][31][32] The result of dry etching in normal incidence are metasurfaces with randomly distributed nanofeatures, yet with a well-controlled and predictive distribution of properties that determine the effective optical properties of the layer from mixing formula rules of the constituents (i.e., glass features and air vacancies). In this work we modify technique (2), since being a mask-based method, it enables the formation and control over the nanoparticle (NP) mask based on prior knowledge, and anisotropy is obtained by tilting the incidence angle of the ion beam with respect to the mask. ...
Birefringent materials—which are highly needed in high power laser systems—may be limited in usage due to the laser‐induced damage threshold of traditional birefringent materials. This work reports here on all‐glass metasurfaces, fabricated by angled etching through sacrificial metal nanoparticle (NP) etching masks, for generation of effective birefringence in the formed layer. As a result, a fused silica metasurface, monolithic to the underlying substrate, is demonstrated to exhibit a birefringence of 6.57° under 375 nm illumination. Full‐wave analysis shows a good agreement with the measurement and presents potential paths forward to increasing the effective metasurface birefringence. This is the first demonstration, to the best of knowledge, of an etching technique to obtain the resulting tilted pillar‐like nanofeatures. The anisotropy of the metasurface nanoelements along the two window in‐plane major axes presents different effective paths for the two polarizations and thus generates birefringence in a nonbirefringent material. Additionally, the imparted anisotropy lends itself to manipulation of physical properties of the surface as well, with metasurface feature orientation suppressing water flow along one principal axis and giving rise to water flow steering capabilities.
... [29] Existing techniques for construction of a substrate-engraved MS that could be practically applied to a large optical aperture consist of directional dry etching processes that either (i) take advantage of ion bombardment or the creation of in situ nucleation centers [30,31] or (ii) utilize masks to guide the etching process. [29,32,33] Metasurfaces generated by both techniques could provide solutions to high power laser systems, which require optics [34] of dimensions ≈1 m 2 and a MS feature center-to-center spacing less than ≈100 nm for operation in the ultraviolet wavelengths. Fabrication of such structures for usage in the UV necessitates an unfathomable ≈100 trillion features per optic. ...
... Further discussion of metasurfaces with feature geometries ranging from vertical sidewalls to the completely sloped as shown in Figure 1 can be found elsewhere. [32,38] As the targeted application is a broadband AR layer with minimized reflection across the ultraviolet (UV)-visible-nearinfrared (NIR), the impact increasing the aspect ratio has on the AR performance can be investigated through transfer matrix analysis. For this work, the incoming light has an angle of incidence of 10°with respect to the surface normal and is P-polarized to match measurements that will be presented later, although we note that for near-normal incidence there is not a large variation between P-and S-polarization. ...
... Using the basic scheme, previous work utilizing traditional solid-state dewetting to fabricate an ensemble of gold nanoparticles to function as an etching mask yielded a MS-A.R. ≈ 1.5. [29] An advancement we reported recently to mask formation utilized a "seeded" dewetting technique of gold, [32] growing the mask nanoparticles while maintaining their period, and thus yielding MS-A.R. ≈ 3. Even though gold provides numerous advantages as a mask material, such as forming a small period and oxidation-resistant nanoparticles, the key limitation of gold utilization was that its mask sputters off too easily while etching, hindering production of a high MS-A.R. Therefore, following a material experimental study searching for metal films capable of forming nanoparticle masks under dewetting with the spatial scale required, while simultaneously exhibiting a characteristic sputter rate lower than gold (the limiting factor for gold), we have identified platinum as a better material of choice. ...
For many optics technologies, such as display screens, solar cells, laser systems, and eyeglasses, antireflective (AR) coatings are well integrated; these applications frequently benefit from the ability to function as broadband AR. Here, all‐glass metasurfaces are reported on, exhibiting a measured reflectance of 0.18% ± 0.23% per interface, averaged across wavelengths spanning from 350 nm (ultraviolet) to 2350 nm (mid‐infrared); to the best of knowledge, this is the first‐ever demonstration of an AR layer capable of this. Furthermore, acceptance angles up to 100° (angle of incidence = ±50°) results in %R < 0.6% per interface over the band 350–1300 nm for P‐polarization and S‐polarization, with wavelength averaged reflectance values 0.04% ± 0.05% and 0.11% ± 0.15%, respectively – another technological first. The process advancements presented here allow for reflectance suppression over a broad range of wavelengths, angles, and polarizations.
... The requirement for large-aperture optics and nanoscale feature spacing brings the focus to rAR technologies; within this subcategory, there are two common approaches: an in situ maskless approach, and an etching mask approach. The latter etching mask approach enables additional control over the Research Article nanoscale MS feature size, spacing, and shape, and consequently is the fabrication method of choice for this work [18][19][20][21]. In addition to AR technologies, this mask-based technology has recently been used to demonstrate optics element patterning and birefringence from a nonbirefringent material [22,23]. ...
... The etched structure is depicted in the electron micrograph in Fig. 1. Dewetting of gold on fused silica, in addition to the MS fabrication process discussed here, has been well documented elsewhere [18,19,[29][30][31][32]. After etching, semiconductor-grade gold etchant is used to remove any residual metal, resulting in the all-glass metasurface. ...
... The MS portrayed in Fig. 1 corresponds to the red 'x' on the contour plot in Fig. 2. Experimental reflectance measurements of this sample at 351-nm incident light yielded 0.37% R, agreeing very well with the model's predicted reflectance of 0.41%. The agreement between the model and fabricated structures has been reported multiple times before, so we encourage the readers to refer to those publications for more details [18][19][20][21]. Reflectance contour plot from a metasurface with feature sidewalls that are 65% sloped. ...
The field of optical metasurfaces is a rapidly growing field due to its potential for the generation of thin optics that have relatively complex geometry while also having flexible functionality. In particular, high power laser systems would benefit from optical metasurfaces capable of beam shaping with optics that may induce less accumulation of nonlinearity and be engineered to incorporate thinner optics. Furthermore, metasurface technology may be harnessed to offer additional laser optics enhancements such as improved anti-reflective layer designs.
One of the limitations facing metasurface technology for high power laser optics is the necessity for both scalability and laser intensity durability. The principal challenge of metasurface creation arises from needing to control local optical properties by tailoring the engineered surface at sub-wavelength scales, while being able to uniformly replicate these morphological features across dimensions typically used with laser optics, i.e. up to the meter scale. Nanofeature patterning techniques in use today include FIB and e-beam lithography that are limited in their scalability, and soft material imprinting which suffers from reduced durability. Following the fabrication of such a metasurface, it remains an open question how this engineered surface will perform under high power laser irradiation.
To obtain scalability and robustness when fabricating large-scale metasurfaces as well as characterize their damage performance, we are developing a durable metasurface technology that does not involve permanent deposition of other materials, i.e. we are just patterning the substrate material. The resultant metasurface generation consists of (1) mask fabrication via thermal annealing of a deposited thin metal film, (2) etching through the mask, and (3) mask removal. In this presentation, we will describe how to fabricate these surfaces and discuss the control we have over the produced metasurfaces via manipulation of the processing parameters. Data and discussion pertaining to the laser damage performance of these engineered large-scale metasurfaces will be presented. This method expands metasurface application fields of interest to areas utilizing high power lasers and, more broadly, to fields that necessitate large and robust optics.
Traditional multilayer antireflection (AR) surfaces are of significant importance for numerous applications, such as laser optics, camera lenses, and eyeglasses. Recently, technological advances in the fabrication of biomimetic AR surfaces capable of delivering broadband omnidirectional high transparency combined with self-cleaning properties have opened an alternative route toward realization of multifunctional surfaces which would be beneficial for touchscreen displays or solar harvesting devices. However, achieving the desired surface properties often requires sophisticated lithography fabrication methods consisting of multiple steps. In the present work, we show the design and implementation of mechanically robust AR surfaces fabricated by a lithography-free process using thermally dewetted silver as an etching mask. Both-sided nanohole (NH) surfaces exhibit transmittance above 99% in the visible or the near-infrared ranges combined with improved angular response at an angle of incidence of up to θi = 60°. Additionally, the NHs demonstrate excellent mechanical resilience against repeated abrasion with cheesecloth due to favorable redistribution of the shearing mechanical forces, making them a viable option for touchscreen display applications.
We investigate laser-induced dewetting of Au films to form nanoparticles with a controlled distribution and to alter these properties spatially with laser parameters for applications of large aperture meta-optics. By performing laser line scans under various parameter space conditions (power, speed, and beam size), we observe that laser power is an effective knob for adjusting the dewetting process while scan speed is not. Temperature numerical calculations show that the scan speeds used in this parameter space do not introduce a large temperature variation but the laser power does. By correlating calculated temperatures and associated experimental dewetting results, we confirm that local temperature is the driving factor in the laser-induced dewetting process. Furthermore, based on in situ thermal emission imaging, the thermal response time is estimated as ∼2 ms and a self-terminating characteristic of the laser-induced dewetting process is observed. This self-terminating effect results in an insignificant change in subsequent laser scans, contributing to the robustness of this process for large area dewetting patterning by beam rastering. Based on these findings, we successfully demonstrate an inch round globe-shaped pattern consisting of Au nanoparticles.
