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Examples of the grayscale lithography applications made by the DWL-series systems from Heidelberg Instruments: (A) Diffraction optical elements, IGI; (B) “Moth-eye” microlenses array, ShenZhen Nahum-Eli Optical Technology Inc, (C) Retro-reflector design, karmic.ch.
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Grayscale lithography is used to produce three-dimensional (3D) structures on micro- and nanoscale. During the last decade, micro-optics and other applications were actively pushing the market demand for such structures. Direct-write systems that use lasers and heated scanning probes can be used for high-precision grayscale micro- and nanolithograp...
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Citations
... In recent years, ultrafast direct laser writing (DLW) has become a popular and costeffective method for facilitating the fabrication process [23,24]. Several strategies have explored the inclusion of this technique, for example, 3D laser-assisted lithography, where electron beam lithography is substituted in the exposure of the photoresist [25,26], or oblique engraving, which can be achieved by significantly tilting the substrate with respect to the incident laser beam [27,28]. ...
Blazed gratings are periodic surface structures of great interest for applications such as friction control, light trapping, and spectrometry. While different laser processing methods have been explored to produce these elements, they have not yet surpassed conventional surface manufacturing techniques, often based on lithography processes or mechanical ruling. This work introduces a new approach based on the combination of ultrashort pulses and triangular beam shaping, which enables the generation of asymmetrical grooves in a single step. The main advantage of this strategy is that by simply changing the laser processing direction we can induce a significant modification in the ratio of asymmetry between the sidewall angles of the machined channels. The paper includes a comprehensive study, which has been supported by statistical tools, of the effect of this and other experimental parameters on the morphology of grooves machined on stainless steel. As a result, we achieved a wide range of geometries, with asymmetry ratios spanning from 1 to 5 and channel depths between 3 and 15 µm. Furthermore, we demonstrate the validity of the approach through the successful manufacture of blazed gratings of various slopes. The results reflect the versatility and cost-efficiency of the proposed fabrication strategy, and thus its potential to streamline the production of sawtooth gratings and other devices that are based on asymmetrical features.
... The feasibility of manufacturing TLDOEs was not taken into account in detail, but it can be assumed that their fabrication is challenging. Nevertheless, depending on the specific materials employed, it should be possible to use well-established fabrication steps such as, for example, grayscale lithography [28], ion beam etching [29], precision glass molding [30], or polymer UV molding [31] to assemble a prototype, whereas the implementation of layer-to-layer-alignment is crucial. For systems using fluids, state-of-the-art manufacturing technologies for microfluidic components [32] can be applied. ...
Diffractive optical elements (DOEs) fundamentally provide the possibility to simultaneously utilize multiple orders for different imaging functions within a system. However, to take advantage of this property, it is necessary to tailor the assignment of specific wavelengths or wavelength ranges with high diffraction efficiency to specific diffraction orders. To achieve this wavelength-selective assignment to different orders, simple diffractive profile shapes are not suitable; instead, multilayer DOEs are required. In this study, we conducted theoretical, scalar investigations on the diffraction efficiency of triple-layer double-relief DOEs for the purpose of tailored wavelength selectivity. Specific materials such as nanocomposites, layer materials, and high-refractive-index liquids with strong dispersion were included, in addition to inorganic glasses, to enable wide design freedom for wavelength selectivity across multiple orders. To simultaneously account for both positive and negative orders, specific material combinations featuring intersecting or touching dispersion curves were utilized. For various material combinations, we calculated significantly different efficiency profiles for multiple orders by varying the relief depths. Further, we discuss the possibility of fine-tuning the efficiency profiles by using high-index liquids as an intermediate layer between two solid profiles, whose dispersion properties can be varied continuously or at least in small steps.
... photolithography or direct machining methods. Moreover, fabrication of highly-complex elements by binary photolithography is fundamentally limited due to per-step accumulated error and practically-bounded number of possible etching steps; grayscale-photolithography, which overcomes some of these limitations, is typically complicated by high sensitivity to material and process parameters and the requirement for complex illumination or scanning 1,13 . ...
Diffractive optical elements (DOEs) have a wide range of applications in optics and photonics, thanks to their capability to perform complex wavefront shaping in a compact form. However, widespread applicability of DOEs is still limited, because existing fabrication methods are cumbersome and expensive. Here, we present a simple and cost-effective fabrication approach for solid, high-performance DOEs. The method is based on conjugating two nearly refractive index-matched solidifiable transparent materials. The index matching allows for extreme scaling up of the elements in the axial dimension, which enables simple fabrication of a template using commercially available 3D printing at tens-of-micrometer resolution. We demonstrated the approach by fabricating and using DOEs serving as microlens arrays, vortex plates, including for highly sensitive applications such as vector beam generation and super-resolution microscopy using MINSTED, and phase-masks for three-dimensional single-molecule localization microscopy. Beyond the advantage of making DOEs widely accessible by drastically simplifying their production, the method also overcomes difficulties faced by existing methods in fabricating highly complex elements, such as high-order vortex plates, and spectrum-encoding phase masks for microscopy.
... This technique enables the fabrication of almost arbitrarily shaped continuous relief structures with maximum flexibility in local variation, achieving structural resolutions down to the sub-µm range. Via suitable control of the exposure dose and selection of the appropriate photo-sensitive resist, diffractive, refractive, and hybrid 2.5D structures with depths of several 10 µm can be produced [1][2][3][4]. Here, the term "hybrid" refers to a combination of refractive and diffractive structures. ...
... Disadvantages of this method include long writing times and the occurrence of stitching effects, i.e., inaccuracies in the aligned positioning of consecutively exposed areas of limited extension, making it difficult to structure large areas. Alternatives are mask-based lithographic gray tone processes, with halftoning, thin-film coatings, or HEBS glass-based approaches being examples of gray tone masks offering locally variable transparency [2][3][4][5][6][7][8]. The process of exposure is faster compared to direct laser writing, but the fabrication of the gray tone masks is demanding and in addition, the option of quickly modifying the structures to be exposed is eliminated. ...
Annular lithography is a recently introduced, flexible technique that has been tailored to the fabrication of rotationally symmetric optical structures in the meso and micro range. The optical concept for the exposure tool is based on a combination of axicons with movable components that create a ring-shaped light distribution with variable diameter in the image plane. This contribution demonstrates for the first time the use of gray tone exposure in annular lithography to fabricate continuous relief structures, overcoming the previous limitation using binary structures. For the controlled exposure of the continuous relief structures, the sensitivity curve of the resist, the exposure dose decreasing with increasing ring diameter, and the exposure time have to be considered. A control and simulation tool is introduced to provide radius-dependent exposure data and, furthermore, to control and iteratively improve the fabricated structures. To demonstrate the gray tone capabilities, various diffractive elements as well as refractive spherical and aspherical elements with a maximum diameter of ~6 mm and a maximum height of 4 µm are shown as examples. Profile shape measurements of fabricated elements show good agreement with the expectations.
... Taking inspiration from similar challenges in microoptic fabrication, grayscale lithography offers a solution to mitigate the staircase effect. Grayscale lithography is a novel approach in photolithography for 2.5D patterning (x,y,z) with ultrasmooth surfaces that exhibits improved shape accuracy [57,58]. In 2019, Nanoscribe GmbH & Co launched the Quantum X platform that commercialized maskless grayscale lithography for microoptics made via 2PP, a process called "Two-Photon Grayscale Lithography" (2GL ® ) [59,60]. ...
Microneedles and, subsequently, microneedle arrays are emerging miniaturized medical devices for painless transdermal drug delivery. New and improved additive manufacturing methods enable novel microneedle designs to be realized for preclinical and clinical trial assessments. However, current literature reviews suggest that industrial manufacturers and researchers have focused their efforts on one-size-fits-all designs for transdermal drug delivery, regardless of patient demographic and injection site. In this perspective article, we briefly review current microneedle designs, microfabrication methods, and industrialization strategies. We also provide an outlook where microneedles may become personalized according to a patient’s demographic in order to increase drug delivery efficiency and reduce healing times for patient-centric care.
... This disadvantage is in general compensated for by avoiding the design and fabrication of complicated and costly masks, a higher flexibility in possible shapes and the steadily decreasing process time with modern exposure systems. Thus, the exposure using a direct laser writer allows for rapid and cost-effective prototyping as shown for example by Grushina (2019). In the following, it will be shown how grayscale lithography can be used for the manufacturing of 3D microfluidic valve structures in silicon and glass substrates. ...
A fabrication strategy for high-efficiency passive three-dimensional microfluidic valves with no mechanical parts fabricated in silicon and glass substrates is presented. 3D diffuser-nozzle valve structures were produced and characterized in their added value in comparison to conventional diffuser-nozzle valve designs with rectangular cross sections. A grayscale lithography approach for 3D photoresist structuring combined with a proportional transfer by reactive ion etching allowed to transfer 3D resist valve designs with high precision into the targeted substrate material. The efficiency with respect to the rectification characteristics or so-called diodicity of the studied valve designs is defined as the ratio of the pressure drops in backward and forward flow directions. The studied valve designs were characterized experimentally as well as numerically based on finite element simulations with overall matching results that demonstrate a significantly improved flow rectification of the 3D valves compared to the corresponding conventional structure. Our novel 3D valve structures show, for instance, even without systematic optimization a measured diodicity of up to 1.5 at low flow rates of only about 10 μl/s.
... [6][7][8][9][10][11] Thus far, the mainstream approaches for accurate nanofabrication with arbitrary shapes are photolithography and laser direct write lithography. [12][13][14][15][16][17][18][19][20][21][22] Photolithography can provide large scale patterning and laser direct write lithography has shown its great potential in the fabrication of complex threedimensional micro-nano structures. However, they suffer from their limited pattern resolution by the intrinsic property of light diffraction. ...
Nanolithography techniques providing good scalability and feature size controllability are of great importance for the fabrication of integrated circuits (IC), MEMS/NEMS, optical devices, nanophotonics, etc. Herein, a cost-effective, easy access, and high-fidelity patterning strategy that combines the high-resolution capability of maskless plasmonic lithography with the spatial morphology controllability of grayscale lithography is proposed to generate the customized pattern profile from microscale to nanoscale. Notably, the scaling effect of gap size in plasmonic lithography with a contact bowtie-shaped nanoaperture (BNA) is found to be essential to the rapid decay characteristics of an evanescent field, which leads to a wide energy bandwidth of the required optimal dose to record pattern in per unit volume, and hence, achieves the volumetrically scalable control of the photon energy deposition in the space more precisely. Based on the proper calibration and cooperation of pattern width and depth, a grayscale-patterned map is designed to compensate for the dose difference caused by the loss of the high spatial frequency component of the evanescent field. A Lena nanostructure with varying feature sizes by spatially modulating the exposure dose distribution was successfully demonstrated, and besides, we also successfully generated a microlens array (MLA) with high uniformity. The practical patterning method makes plasmonic lithography significant in the fabrication of functional nanostructures with high performance, including metasurfaces, plasmonics, and optical imaging systems.
... Thus, addressing these challenges should result in the measured focusing efficiencies approaching the simulated values of nearly 90% across the visible. Advancements in the multiphoton laser technology to improve fabrication area and throughput could enable the production of larger area lenses and achromatic MLAs [54][55][56] . We believe the achromats presented in this work will inspire further research into hybrid diffractive/refractive systems that manipulate light for applications, including near-eye displays, lightweight cameras, light-field imagers, and light-field displays. ...
Compact visible wavelength achromats are essential for miniaturized and lightweight optics. However, fabrication of such achromats has proved to be exceptionally challenging. Here, using subsurface 3D printing inside mesoporous hosts we densely integrate aligned refractive and diffractive elements, forming thin high performance hybrid achromatic imaging micro-optics. Focusing efficiencies of 51–70% are achieved for 15μm thick, 90μm diameter, 0.3 numerical aperture microlenses. Chromatic focal length errors of less than 3% allow these microlenses to form high-quality images under broadband illumination (400–700 nm). Numerical apertures upwards of 0.47 are also achieved at the cost of some focusing efficiency, demonstrating the flexibility of this approach. Furthermore, larger area images are reconstructed from an array of hybrid achromatic microlenses, laying the groundwork for achromatic light-field imagers and displays. The presented approach precisely combines optical components within 3D space to achieve thin lens systems with high focusing efficiencies, high numerical apertures, and low chromatic focusing errors, providing a pathway towards achromatic micro-optical systems.
... photolithography or direct machining methods. Moreover, fabrication of highly-complex elements by binary photolithography is fundamentally limited due to per-step accumulated error and practically-bounded number of possible etching steps; grayscale-photolithography, which overcomes some of these limitations, is typically complicated by high sensitivity to material and process parameters and the requirement for complex illumination or scanning 1, 13 . ...
Diffractive optical elements (DOEs) have a wide range of applications in optics and photonics, thanks to their capability to perform complex wavefront shaping in a compact form. However, widespread applicability of DOEs is still limited, because existing fabrication methods are cumbersome and expensive. Here, we present a simple and cost-effective fabrication approach for solid, high-performance DOEs. The method is based on conjugating two nearly refractive index-matched solidifiable transparent materials. The index matching allows for extreme scaling up of the elements in the axial dimension, which enables simple fabrication of a template using commercially available 3D printing at tens-of-micrometer resolution. We demonstrated the approach by fabricating and using DOEs serving as microlens arrays, vortex plates, including for highly sensitive applications such as vector beam generation and super-resolution microscopy using MINSTED, and phase-masks for three-dimensional single-molecule localization microscopy. Beyond the advantage of making DOEs widely accessible by drastically simplifying their production, the method also overcomes difficulties faced by existing methods in fabricating highly complex elements, such as high-order vortex plates, and spectrum-encoding phase masks for microscopy.
... One way to create different colors over the same substrate using the multilayer thin film structures (i.e., realizing monolithic color integration) is to create stepwise micro-or nano-cavities. Towards such goal, grayscale lithography [221][222][223][224] and nanoimprint lithography [225][226][227][228][229][230] have been exploited. During the device fabrication process, a thickness-modulated photoresist is commonly employed either as the dielectric layer in the cavity or as the etching mask to transfer the stepwise thickness profile onto the underneath dielectric layer. ...
Recent years have witnessed a rapid development in the field of structural coloration, colors generated from the interaction of nanostructures with light. Compared to conventional color generation based on pigments and dyes, structural color generation exhibits unique advantages in terms of spatial resolution, operational stability, environmental friendliness, and multiple functionality. Here, we discuss recent development in structural coloration based on layered thin films and optical metasurfaces. This review first presents fundamentals of color science and introduces a few popular color spaces used for color evaluation. Then, it elaborates on representative physical mechanisms for structural color generation, including Fabry–Pérot resonance, photonic crystal resonance, guided mode resonance, plasmon resonance, and Mie resonance. Optimization methods for efficient structure parameter searching, fabrication techniques for large-scale and low-cost manufacturing, as well as device designs for dynamic displaying are discussed subsequently. In the end, the review surveys diverse applications of structural colors in various areas such as printing, sensing, and advanced photovoltaics.
