Three-dimensional Laser Lithography Research Articles

Laser-written wave plates inside the silicon enabled by stress-induced birefringence.

Laser writing enables optical functionality by altering the optical properties of materials. To achieve this goal, efforts generally focus on laser-written regions. It has also been shown that birefringence surrounding the modified regions can be exploited for achieving functionality. The effect has been used to fabricate wave plates in glass, with significant potential for other materials. Here, we establish analogous stress control and birefringence engineering inside silicon. We first develop a robust analytical model enabling the prediction of birefringence maps from arbitrary laser-written patterns. Then, we tailor three-dimensional laser lithography to create the first, to the best of our knowledge, polarization-control optics inside silicon.

Intracavity spatiotemporal metasurfaces

Optical metasurfaces are endowed with unparallel flexibility to manipulate the light field with a subwavelength spatial resolution. Coupling metasurfaces to materials with strong optical nonlinearity may allow ultrafast spatiotemporal light field modulation. However, most metasurfaces demonstrated thus far are linear devices. Here, we experimentally demonstrate simultaneous spatiotemporal laser mode control using a single-layer plasmonic metasurface strongly coupled to an epsilon-near-zero (ENZ) material within a fiber laser cavity. While the geometric phase of the metasurface is utilized to convert the laser’s transverse mode from a Gaussian beam to a vortex beam carrying orbital angular momentum, the giant nonlinear saturable absorption of the ENZ material enables pulsed laser generation via the Q-switching process. The direct integration of a spatiotemporal metasurface in a laser cavity may pave the way for the development of miniaturized laser sources with tailored spatial and temporal profiles, which can be useful for numerous applications, such as superresolution imaging, high-density optical storage, and three-dimensional laser lithography.

Simulation Model for Direct Laser Writing of Metallic Microstructures Composed of Silver Nanoparticles

Three-dimensional metallic microstructures find applications as stents in medicine, as ultrabroadband antennas in communications, in micromechanical parts or as structures of more fundamental interest in photonics like metamaterials. Direct metal printing of such structures using three-dimensional laser lithography is a promising approach, which is not extensively applied yet, as fabrication speed, surface quality, and stability of the resulting structures are limited so far. In order to identify the limiting factors, we investigate the influence of light-particle interactions and varying scan speed on heat generation and particle deposition in direct laser writing of silver. We introduce a theoretical model which captures diffusion of particles and heat as well as the fluid dynamics of the photo-resist. Chemical reactions are excluded from the model but particle production is calibrated using experimental data. We find that optical forces generally surmount those due to convection of the photo-resist. Simulations predict overheating of the photo-resist at laser powers similar to those found in experiments. The thermal sensitivity of the system is essentially determined by the largest particles present in the laser focus. Our results suggest that to improve particle deposition and to achieve higher writing speeds in metal direct laser writing, strong optical trapping of the emerging particles is desirable. Furthermore, precise control of the particle size reduces the risk of spontaneous overheating.

Polymer-based MHCG as selective mirror

In this paper, we present the simulation and preparation in IP-Dip material of a polymer grating, which is used as a highly reflective and spectrally selective mirror based on monolithic high-contrast grating (MHCG) geometry. We simulated the power reflectance as a function of the grating parameters and prepared the grating structure in IP-Dip material using three-dimensional laser lithography. The 3D morphology of the prepared devices was analyzed using a scanning electron microscope. Finally, their spectral power reflectance characteristics were measured and compared with the simulations. The prepared and simulated MHCG structures exceeded 70% power reflectance in the narrow spectral region of 740–810 nm.

Dissolving undercut microneedle arrays for multicomponent cutaneous vaccination

The skin is an attractive tissue target for vaccination, as it is readily accessible and contains a dense population of antigen-presenting and immune-accessory cells. Microneedle arrays (MNAs) are emerging as an effective tool for in situ engineering of the cutaneous microenvironment to enable diverse immunization strategies. Here, we present novel dissolving undercut MNAs and demonstrate their application for effective multicomponent cutaneous vaccination. The MNAs are composed of micron-scale needles featuring pyramidal heads supported by undercut stem regions with filleted bases to ensure successful skin penetration and retention during application. Prior efforts to fabricate dissolving undercut microstructures were limited and required complex and lengthy processing and assembly steps. In the current study, we strategically combine three-dimensional (3D) laser lithography, an emerging micro-additive manufacturing method with unique geometric capabilities and nanoscale resolution, and micromolding with favorable materials. This approach enables reproducible production of dissolving MNAs with undercut microneedles that can be tip-loaded with multiple biocargos, such as antigen (ovalbumin) and adjuvant (Poly(I:C)). The resulting MNAs fulfill the geometric (sharp tips and smooth edges) and mechanical-strength requirements for failure-free penetration of human and murine skin to simultaneously deliver multicomponent (antigen plus adjuvant) vaccines to the same cutaneous microenvironment. Cutaneous vaccination of mice using these MNAs induces more potent antigen-specific cellular and humoral immune responses than those elicited by traditional intramuscular injection. Together, the unique geometric features of these undercut MNAs and the associated manufacturing strategy, which is compatible with diverse drugs and biologics, could enable a broad range of non-cutaneous and cutaneous drug delivery applications, including multicomponent vaccination.

Three-Dimensional Printed Surfaces Inspired by Bi-Gaussian Stratified Plateaus.

Wettability of artificial surfaces is attracting increasing attention for its relevant technological applications. Functional performance is often achieved by mimicking the topographical structures found in natural flora and fauna; however, surface attributes inspired by geological landscapes have so far escaped attention. We reproduced a stratified morphology of plateaus with a bi-Gaussian height distribution using a three-dimensional direct laser lithography. The plateau-inspired artificial surface exhibits a hydrophobic behavior even if fabricated from a hydrophilic material, giving rise to a new wetting mechanism that divides the well-known macroscopic Wenzel and Cassie states into four substates. We have also successfully applied the plateau-inspired structure to droplet manipulation.

Polymer-based holograms with individually adjustable structure angle

We present polymer-based holograms with varying structure angle for each individual micrometer-sized pixel. The holograms are numerically calculated utilizing an iterative optimization procedure, including a first-order Taylor series expansion to determine the slope of each pixel. The holograms are fabricated by three-dimensional laser lithography. Due to the small pixel sizes and the individual slope of each pixel, aliases can be avoided and the overall intensity of the desired projection is strongly increased compared to holograms consisting of larger and uniform pixels. Furthermore, the discrepancy between calculated and measured intensity distribution is strongly reduced.

Controlling the shape of 3D microstructures by temperature and light

Stimuli-responsive microstructures are critical to create adaptable systems in soft robotics and biosciences. For such applications, the materials must be compatible with aqueous environments and enable the manufacturing of three-dimensional structures. Poly(N-isopropylacrylamide) (pNIPAM) is a well-established polymer, exhibiting a substantial response to changes in temperature close to its lower critical solution temperature. To create complex actuation patterns, materials that react differently with respect to a stimulus are required. Here, we introduce functional three-dimensional hetero-microstructures based on pNIPAM. By variation of the local exposure dose in three-dimensional laser lithography, we demonstrate that the material parameters can be altered on demand in a single resist formulation. We explore this concept for sophisticated three-dimensional architectures with large-amplitude and complex responses. The experimental results are consistent with numerical calculations, able to predict the actuation response. Furthermore, a spatially controlled response is achieved by inducing a local temperature increase by two-photon absorption of focused light.

3D laser lithographic fabrication of hollow microneedle mimicking mosquitos and its characterisation

Microneedles mimicking mosquitos were fabricated by employing a three-dimensional laser lithography. An ultra-precision three-dimensional laser lithography system 'Nanoscribe GT' is employed. On the basis of two-photon absorption phenomenon, an extremely small space of less than 200 nm in the photocurable polymer material is cross-linked, where a laser beam is focused. The total cross-linked space finally emerges after development process. First a bundled needle comprising three parts was fabricated, which imitates central hollow labrum of sucking blood, and two side solid maxillae having jagged edges. Second, a practical needle comprising two parts was proposed and fabricated. The functions of three-piece mosquito's proboscis (one labrum and two maxillae) are integrated to two parts. Each half-needle has semi-circular channel and jagged edges. By combining the two-halves, one hollow microneedle is realised. Alternative motion like mosquito maxillae is possible. Fluid is introduced into the channel through small holes in the wall, and is drawn up by capillary force. Reduction in number of microneedles simplifies both fabrication process and drive system for puncturing. It was experimentally confirmed that the needle successfully penetrates PDMS skin. The effectiveness of alternative motion of two parts with 90° phase to each other was also investigated.

Intregrating metallic wiring with three-dimensional polystyrene colloidal crystals using electron-beam lithography and three-dimensional laser lithography

We demonstrate a method to fabricate narrow, down to a few micron wide metallic leads on top of a three-dimensional (3D) colloidal crystal self-assembled from polystyrene (PS) nanospheres of diameter 260 nm, using electron-beam lithography. This fabrication is not straightforward due to the fact that PS nanospheres cannot usually survive the harsh chemical treatments required in the development and lift-off steps of electron-beam lithography. We solve this problem by increasing the chemical resistance of the PS nanospheres using an additional electron-beam irradiation step, which allows the spheres to retain their shape and their self-assembled structure, even after baking to a temperature of 160 °C, the exposure to the resist developer and the exposure to acetone, all of which are required for the electron-beam lithography step. Moreover, we show that by depositing an aluminum oxide capping layer on top of the colloidal crystal after the e-beam irradiation, the surface is smooth enough so that continuous metal wiring can be deposited by the electron-beam lithography. Finally, we also demonstrate a way to self-assemble PS colloidal crystals into a microscale container, which was fabricated using direct-write 3D laser-lithography. Metallic wiring was also successfully integrated with the combination of a container structure and a PS colloidal crystal. Our goal is to make a device for studies of thermal transport in 3D phononic crystals, but other phononic or photonic crystal applications could also be envisioned.

Automated aberration correction of arbitrary laser modes in high numerical aperture systems.

Controlling the point-spread-function in three-dimensional laser lithography is crucial for fabricating structures with highest definition and resolution. In contrast to microscopy, aberrations have to be physically corrected prior to writing, to create well defined doughnut modes, bottlebeams or multi foci modes. We report on a modified Gerchberg-Saxton algorithm for spatial-light-modulator based automated aberration compensation to optimize arbitrary laser-modes in a high numerical aperture system. Using circularly polarized light for the measurement and first-guess initial conditions for amplitude and phase of the pupil function our scalar approach outperforms recent algorithms with vectorial corrections. Besides laser lithography also applications like optical tweezers and microscopy might benefit from the method presented.

Wiring up pre-characterized single-photon emitters by laser lithography.

Future quantum optical chips will likely be hybrid in nature and include many single-photon emitters, waveguides, filters, as well as single-photon detectors. Here, we introduce a scalable optical localization-selection-lithography procedure for wiring up a large number of single-photon emitters via polymeric photonic wire bonds in three dimensions. First, we localize and characterize nitrogen vacancies in nanodiamonds inside a solid photoresist exhibiting low background fluorescence. Next, without intermediate steps and using the same optical instrument, we perform aligned three-dimensional laser lithography. As a proof of concept, we design, fabricate, and characterize three-dimensional functional waveguide elements on an optical chip. Each element consists of one single-photon emitter centered in a crossed-arc waveguide configuration, allowing for integrated optical excitation and efficient background suppression at the same time.

Optical properties of woodpile photonic crystals produced by three-dimensional laser lithography

Photonic crystals having a woodpile lattice structure with the lateral sizes of up to 200 × 200 μm and lattice period of 1 to 2 μm have been produced by additive three-dimensional laser lithography. The sample structure has been analyzed by optical and scanning electron microscopy. The ideal woodpile consists of “logs” with a rectangular cross section but, in the synthesized structures, the angles are rounded. Calculations of the photonic band structure of woodpiles, in which the cross sections of logs are specified by the Lame curves, have made it possible to estimate the influence of the rounding on the optical properties. Due to significant sample sizes, patterns of optical diffraction in white and monochromatic light have been studied experimentally. The experimental results have been interpreted using calculations of diffraction patterns in the Born approximation of scattering theory.

Fabrication of Microneedle Mimicking Mosquito Proboscis Using Nanoscale 3D Laser Lithography System

A mosquito’s proboscis, which is used for sucking blood, consists of seven complicated parts. For example, the labrum has a hollow structure, and the maxillae have micrometer-sized tooth like projections on its tip. In this study, microneedles imitating one labium and two maxillae were fabricated using a precision three-dimensional laser lithography system “Nanoscribe.” The maximum length of the fabricated microneedle was 2.0 mm, the minimum length required to reach human capillary blood vessel underneath the epidermis.

Gold triple-helix mid-infrared metamaterial by STED-inspired laser lithography.

In analogy to wire-grid polarizers for linear polarization, metal-helix metamaterials can act as broadband circular polarizers. This concept has brought circular-polarization capabilities to mid-infrared and terahertz frequencies, which were previously difficult to access. Due to the lack of rotational symmetry, however, single-helix metamaterials exhibit unwanted circular-polarization conversions. Recent theoretical work showed that conversions can be fully eliminated by intertwining N=3 or 4 helices within each unit cell. While direct laser writing in positive-tone photo-resist yielded good results for single-helix metamaterials operating at mid-infrared frequencies, the axial resolution is insufficient for N-helix metamaterials. Here, we use stimulated emission depletion-inspired three-dimensional laser lithography to fabricate such microstructures. We measure all entries of the Jones transmission and reflection matrices and show experimentally that polarization conversions are minimized, in good agreement with theory.

1P1-R05 光造形装置による蚊の口針を3次元的に模擬したマイクロニードルの作製

Proboscis of a mosquito for sucking blood consists of complicated seven parts. For example, labrum has hollow structure, and maxilla has micrometer-sized toothlike projections on its tip part. In this study, microneedls imitating one labium and two maxillae were fabricated using precision three-dimensional laser lithography system "Nanoscribe" Maximum length of the fabricated microneedle is 1.5 mm, which is minimal to reach to capillary blood vessel underneath human epidermis.

Fabrication of submicron structures by three-dimensional laser lithography

This study was partially supported by the Government of the Russian Federation (project no. 074U01) and the Russian Foundation for Basic Research (project no. 130200186).

Three‐dimensional laser lithography

AbstractIn the last decades micro‐ and nanotechnology have made enormous progress. One of the key success factors is the continuous improvement of lithographic techniques which are the driving forces of innovation in many industrial areas. So far, lithography on the sub‐micrometer scale has mostly been limited to planar objects. Trends towards further miniaturization and high‐density integration call for disruptive developments of production standards. The next logical step is to go from planar two‐dimensional lithography to the third dimension.