Three-dimensional Direct Laser Research Articles

Brillouin Light Scattering Characterisation of Gray Tone 3D Printed Isotropic Materials.

Three-dimensional direct laser writing technology enables one to print polymer microstructures whose size varies from a few hundred nanometers to a few millimeters. It has been shown that, by tuning the laser power during writing, one can adjust continuously the optical and elastic properties with the same base material. This process is referred to as gray-tone lithography. In this paper, we characterize by Brillouin light scattering the complex elastic constant of different reticulated isotropic polymers, at longitudinal phonon frequencies of the order of 16 GHz. We estimate the real part of the constant to vary from 7 to 11 GPa as a function of laser power, whereas its imaginary part varies between 0.25 and 0.6 GPa. The linear elastic properties are further measured at a fixed laser power as a function of temperature, from C to C. Overall, we show that our 3D printed samples have a good elastic quality with high Q factors only ten times smaller than fused silica at hypersonic frequencies.

Three-dimensional direct laser writing of biomimetic neuron interfaces in the era of artificial intelligence: principles, materials, and applications

The creation of biomimetic neuron interfaces (BNIs) has become imperative for different research fields from neural science to artificial intelligence. BNIs are two-dimensional or three-dimensional (3D) artificial interfaces mimicking the geometrical and functional characteristics of biological neural networks to rebuild, understand, and improve neuronal functions. The study of BNI holds the key for curing neuron disorder diseases and creating innovative artificial neural networks (ANNs). To achieve these goals, 3D direct laser writing (DLW) has proven to be a powerful method for BNI with complex geometries. However, the need for scaled-up, high speed fabrication of BNI demands the integration of DLW techniques with ANNs. ANNs, computing algorithms inspired by biological neurons, have shown their unprecedented ability to improve efficiency in data processing. The integration of ANNs and DLW techniques promises an innovative pathway for efficient fabrication of large-scale BNI and can also inspire the design and optimization of novel BNI for ANNs. This perspective reviews advances in DLW of BNI and discusses the role of ANNs in the design and fabrication of BNI.

Structuring light using solgel hybrid 3D-printed optics prepared by two-photon polymerization.

Three-dimensional direct laser writing based on a two-photon polymerization process of hybrid organic-inorganic material was used to print micrometer-scale refractive phase elements that were designed to manipulate incoming Gaussian beams into line and square intensity-flattened profiles. Here we present new results of shaping light beams, enabled by tailoring a two-photon absorption process for printing hybrid material structures based on a fast solgel process. The optical design and calculations of the optical elements are described, along with characterization of their performance in manipulating incoming light beams. The novelty described in this work, to the best of our knowledge, is the implementation of 3D solgel materials as better and improved micro-optics. This new ability provides upgraded 3D high resolution and smooth, printed optical phase structures using tailored hybrids with improved optical and mechanical properties compared to standard common photoresists. This opens new and exciting opportunities for compact and robust beam shaping by reaching glassy material properties and overcoming limitations of organic polymers.

3D printed hybrid refractive/diffractive achromat and apochromat for the visible wavelength range.

Three-dimensional (3D) direct laser writing is a powerful technology to create nano- and microscopic optical devices. While the design freedom of this technology offers the possibility to reduce different monochromatic aberrations, reducing chromatic aberrations is often neglected. In this Letter, we successfully demonstrate the combination of refractive and diffractive surfaces to create a refractive/diffractive achromat and show, to the best of our knowledge, the first refractive/diffractive apochromat by using DOEs and simultaneously combining two different photoresists, namely IP-S and IP-n162. These combinations drastically reduce chromatic aberrations in 3D printed micro-optics for the visible wavelength range. The optical properties, as well as the substantial reduction of chromatic aberrations, are characterized, and we outline the benefits of 3D direct laser written achromats and apochromats for micro-optics.

Three-Dimensional Direct Laser Writing of PEGda Hydrogel Microstructures with Low Threshold Power using a Green Laser Beam

Three-Dimensional Direct Laser Writing of PEGda Hydrogel Microstructures with Low Threshold Power using a Green Laser Beam

Challenges in a Hybrid Fabrication Process to Generate Metallic Polarization Elements with Sub-Wavelength Dimensions.

We report on the challenges in a hybrid sub-micrometer fabrication process while using three dimensional femtosecond direct laser writing and electroplating. With this hybrid subtractive and additive fabrication process, it is possible to generate metallic polarization elements with sub-wavelength dimensions of less than 400 nm in the cladding area. We show approaches for improving the adhesion of freestanding photoresist pillars as well as of the metallic cladding area, and we also demonstrate the avoidance of an inhibition layer and sticking of the freestanding pillars. Three-dimensional direct laser writing in a positive tone photoresist is used as a subtractive process to fabricate free-standing non-metallic photoresist pillars with an area of about 850 nm × 1400 nm, a height of 3000 nm, and a distance between the pillars of less than 400 nm. In a subsequent additive fabrication process, these channels are filled with gold by electrochemical deposition up to a final height of 2200 nm. Finally, the polarization elements are characterized by measuring the degree of polarization in order to show their behavior as quarter- and half-wave plates.

Direct femtosecond laser writing of inverted array for broadband antireflection in the far-infrared

The surface optical loss in optical windows is primarily attributed to Fresnel reflection at the interface between air and substrate of high refractive index materials such as zinc sulfide (ZnS). In this study, the concave antireflective subwavelength structures (ASS) on ZnS have been numerically and experimentally investigated to obtain high transmittance over a wide bandwidth in the far-infrared range from 7 μm to 14 μm. The mechanism for transmittance enhancement is explored by localized field selective enhancement in structures based on Wood-Rayleigh law, also being confirmed by the light energy flowing in Poynting vector distribution. The geometric parameters including shapes, period, and depth of as-designed array have been specifically optimized by finite-difference time-domain (FDTD) method and effective medium theory (EMT). Hereby, three-dimensional direct femtosecond laser writing (3D fs-DLW) is employed to fabricate the ASS in inverted conical and pyramidal array with the largest transmittance reaching to 85.2% in 9 μm wavelength and robust mechanical characteristics (hardness >2.39 GPa), expecting to be of great potential applications in infrared optical windows.

Three-Dimensional Direct Laser Writing of PEGda Hydrogel Microstructures with Low Threshold Power using a Green Laser Beam

Three-Dimensional Direct Laser Writing of PEGda Hydrogel Microstructures with Low Threshold Power using a Green Laser Beam

Self-Compensating Liquid-Repellent Surfaces with Stratified Morphology.

Artificial liquid-repellent surfaces have recently attracted vast scientific attention; however, achieving mechanical robustness remains a formidable challenge before industrialization can be realized. To this end, inspired by plateaus in geological landscapes, a self-compensating strategy is developed to pave the way for the synthesis of durable repellent surfaces. This self-compensating surface comprises tall hydrophobic structural elements, which can repel liquid droplets. When these elements are damaged, they expose shorter structural elements that also suspend the droplets and thus preserve interfacial repellency. An example of this plateau-inspired stratified surface was created by three-dimensional (3D) direct laser lithography micro-nano fabrication. Even after being subjected to serious frictional damage, it maintained static repellency to water with a contact angle above 147° and was simultaneously able to endure high pressures arising from droplet impacts. Extending the scope of nature-inspired functional surfaces from conventional biomimetics to geological landscapes, this work demonstrates that the plateau-inspired self-compensating strategy can provide an unprecedented level of robustness in terms of sustained liquid repellency.

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.

Near-infrared transmittance enhancement using fully conformal antireflective structured surfaces on microlenses fabricated by direct laser writing

Structured surfaces composed of subwavelength-sized features offer multifunctional properties including antireflective characteristics that are increasingly important for the development of micro-optical components. Here, three-dimensional (3-D) direct laser writing, via two-photon polymerization, is used to fabricate planoconvex spherical microlenses with antireflective structured surfaces. The surfaces are composed of subwavelength-sized conicoid structures, which are arranged fully conformal to the convex surface of the microlenses. The dimensions of the conicoid structures are optimized to effectively reduce Fresnel reflection loss over a wide band in the near-infrared spectral range from 1.4 to 2.2 μm, with a maximum reduction at 1.55 μm. Infrared reflection and transmission measurements are used, in combination with 3-D finite element calculations, to investigate the performance of the microlenses. The experimental results reveal that in the spectral range from 1.4 to 2.2 μm an effective suppression of the Fresnel reflection loss at the convex surface of spherical microlenses can be achieved. The transmittance enhancement is ranging from 1% to 3% for spherical microlenses with antireflective structured surfaces, in comparison to an uncoated reference.

Three-dimensional direct laser written achromatic axicons and multi-component microlenses.

Femtosecond 3D printing is an important technology for manufacturing nano- and microscopic optical devices and elements. However, most structures in the past have been created using only one photoresist at a time, thus limiting potential applications. In this Letter, we successfully demonstrate the combination of two different photoresists, namely, IP-S and IP-Dip, to realize multi-component three-dimensional direct laser written optics. We use the combination of IP-S and IP-Dip to correct chromatic aberrations and to realize an achromatic axicon. In a second step, we demonstrate, to the best of our knowledge, the first three-dimensional direct laser written Fraunhofer doublet. We characterize their optical properties and measure the substantial reduction in chromatic aberrations. We outline the possibilities and benefits of creating three-dimensional direct laser written multi-component structures for micro-optics.

Three-dimensional direct laser writing of biomimetic neuron structures.

Building biomimetic neuron structures that emulate the topological features of biological neural networks at multiple scales has been an active area in neuron cell culturing, neuron-chip interface and computer chip design. However, due to the fact that biological neural networks possess extraordinary connectivity and complexity from millimeter down to nanometer scale, with different dendritic branch angles, branch lengths, and branch diameters, previous methods to reproduce the topological features of biological neural networks are either limited to two dimensions or lack of fabrication resolution in building three-dimensional (3D) structures. Here we report on the generation of 3D biomimetic neuron structures at a micrometer scale, with high mechanical stability and controlled topologies by studying the effect of 3D direct laser writing (DLW) on the capillary force. This work provides an optical technology platform to replicate the topological features of biological neural networks and paves the avenue towards more applications of using 3D direct laser writing in engineered neural networks.

Micro-/Nanorobots Propelled by Oscillating Magnetic Fields.

Recent strides in micro- and nanomanufacturing technologies have sparked the development of micro-/nanorobots with enhanced power and functionality. Due to the advantages of on-demand motion control, long lifetime, and great biocompatibility, magnetic propelled micro-/nanorobots have exhibited considerable promise in the fields of drug delivery, biosensing, bioimaging, and environmental remediation. The magnetic fields which provide energy for propulsion can be categorized into rotating and oscillating magnetic fields. In this review, recent developments in oscillating magnetic propelled micro-/nanorobot fabrication techniques (such as electrodeposition, self-assembly, electron beam evaporation, and three-dimensional (3D) direct laser writing) are summarized. The motion mechanism of oscillating magnetic propelled micro-/nanorobots are also discussed, including wagging propulsion, surface walker propulsion, and scallop propulsion. With continuous innovation, micro-/nanorobots can become a promising candidate for future applications in the biomedical field. As a step toward designing and building such micro-/nanorobots, several types of common fabrication techniques are briefly introduced. Then, we focus on three propulsion mechanisms of micro-/nanorobots in oscillation magnetic fields: (1) wagging propulsion; (2) surface walker; and (3) scallop propulsion. Finally, a summary table is provided to compare the abilities of different micro-/nanorobots driven by oscillating magnetic fields.

High-contrast infrared polymer photonic crystals fabricated by direct laser writing.

One-dimensional (1D) photonic crystals (PCs) were fabricated by three-dimensional (3D) direct laser writing using a single polymer to obtain reflectance values approaching that of a gold reference in the near-infrared (near-IR) spectral range. The PCs are composed of alternating compact and low-density polymer layers that provide the necessary periodic variation of the refractive index. The low-density polymer layers are composed of subwavelength-sized pillars which simultaneously serve as a scaffold while also providing refractive index contrast to the adjacent compact polymer layers. The Bruggemann effective medium theory and stratified-layer optical-model calculated reflectivity profiles were employed to optimize the PC's design to operate at a desired wavelength of 1.55μm. After the fabrication, the PC's structure was compared to the nominal geometry using complementary scanning electron microscopy and optical microscopy micrographs identifying a true-to-form fabrication. The performance of the PCs was investigated experimentally using FTIR reflection and transmission measurements. A good agreement between stratified-layer optical-model calculated and measured data is observed. Therefore, we demonstrate the ease of predictive design and fabrication of highly efficient 1D PCs for the IR spectral range using 3D direct laser writing of a single polymer.

Evolution of Optical Diffraction Patterns on Disordered Woodpile Photonic Structures

Using three-dimensional direct laser writing, ordered and disordered photonic woodpile structures have been produced. An ideal woodpile is formed by layers of parallel “logs” turned through 90° with respect to logs of the previous layer. The disorder was specified by a random deviation in the angle with respect to their parallel arrangement in each layer of the woodpile. The quality of samples was tested by scanning electron microscopy. The optical diffraction patterns were studied experimentally on microsamples with different degrees of disorder and structure periods. With an increase in the degree of the disorder, the diffraction patterns changed qualitatively with the preservation of the zero diffraction order and formation of a speckle field pattern by higher diffraction orders.

Sub-10-nm suspended nano-web formation by direct laser writing

A diffraction-limited three-dimensional (3D) direct laser writing (DLW) system based on two-photon polymerization can routinely pattern structures at the 100 nm length scale. Several schemes have been developed to improve the patterning resolution of 3D DLW but often require customized resist formulations or multi-wavelength exposures. Here, we introduce a scheme to produce suspended nano-webs with feature sizes below 10 nm in IP-Dip resist using sub-threshold exposure conditions in a commercial DLW system. The narrowest suspended lines (nano-webs) measured 7 nm in width. Larger ∼20 nm nano-webs were patterned with ∼80% yield at increased laser powers. In addition, closely spaced nano-gaps with a center-to-center distance of 33 nm were produced by patterning vertically displaced suspended lines followed by metal deposition and liftoff. We provide hypotheses and present preliminary results for a mechanism involving the initiation of a percolative path and a strain-induced narrowing in the nano-web formation. Our approach allows selective features to be patterned with dimensions comparable to the sub-10 nm patterning capability of electron-beam lithography (EBL).

Three-dimensional direct laser written graphitic electrical contacts to randomly distributed components

The development of cost-effective electrical packaging for randomly distributed micro/nano-scale devices is a widely recognized challenge for fabrication technologies. Three-dimensional direct laser writing (DLW) has been proposed as a solution to this challenge, and has enabled the creation of rapid and low resistance graphitic wires within commercial polyimide substrates. In this work, we utilize the DLW technique to electrically contact three fully encapsulated and randomly positioned light-emitting diodes (LEDs) in a one-step process. The resolution of the contacts is in the order of 20,upmu hbox {m}, with an average circuit resistance of 29 pm 18,hbox {k}Omega per LED contacted. The speed and simplicity of this technique is promising to meet the needs of future microelectronics and device packaging.

Broadband near-infrared antireflection coatings fabricated by three-dimensional direct laser writing.

Three-dimensional direct laser writing via two-photon polymerization is used to fabricate anti-reflective structured surfaces (ARSSs) composed of subwavelength conicoid features optimized to operate over a wide bandwidth in the near-infrared range from 3700 cm-1 to 6600 cm-1 (2.7-1.52μm). Analytic Bruggemann effective medium calculations are used to predict nominal geometric parameters such as the fill factor of the constitutive conicoid features of the anti-reflective structured surfaces (ARSSs) presented here. The performance of the ARSSs was investigated experimentally using infrared reflection and transmission measurements. An enhancement of the transmittance by 1.35%-2.14% over a broadband spectral range from 3700 cm-1 to 6600 cm-1 (2.7-1.52μm) was achieved. We further report on finite-element-based reflection and transmission data using three-dimensional (3D) model geometries for comparison. A good agreement between experimental results and the finite-element-based numerical analysis is observed once as-fabricated deviations from the nominal conicoid forms are included in the model. 3D direct laser writing is demonstrated here as an efficient method for the fabrication and optimization of ARSSs designed for the infrared spectral range.

Эволюция картин оптической дифракции на неупорядоченных фотонных структурах типа поленница

AbstractUsing three-dimensional direct laser writing, ordered and disordered photonic woodpile structures have been produced. An ideal woodpile is formed by layers of parallel “logs” turned through 90° with respect to logs of the previous layer. The disorder was specified by a random deviation in the angle with respect to their parallel arrangement in each layer of the woodpile. The quality of samples was tested by scanning electron microscopy. The optical diffraction patterns were studied experimentally on microsamples with different degrees of disorder and structure periods. With an increase in the degree of the disorder, the diffraction patterns changed qualitatively with the preservation of the zero diffraction order and formation of a speckle field pattern by higher diffraction orders.