Multi-beam Laser Interference Research Articles

Theoretical study of micro-structure fabrication by multi-beam laser interference lithography with different polarization combinations

In this study, we systematically and comprehensively investigated the influence of polarization angle on the fabrication of micro-structures by multi-beam laser interference lithography. Using theoretical analysis and simulation, we studied the effect of different polarization combinations, i.e. transverse electric (TE) and transverse magnetic (TM) polarization combinations, on the characteristics of the micro-structures fabricated by three-, four-, and six-beam laser interference lithography. We successfully obtained micro-structures with different periodic patterns such as honeycomb dots, quasi-elliptic dots, different square dots, and quasi-triangular dots. The simulation results illustrate that polarization affects the formation of interference patterns, pattern contrasts, and periods. The methods discussed herein are simple, low cost, and allow excellent control over structural parameters, and hence are useful for the micro-structure manufacturing industry.

Thermodynamic processes on a semiconductor surface during in‐situ multi‐beam laser interference patterning

Laser interference has been widely used to produce one-dimensional gratings and more recently has shown great potential for two-dimensional patterning. In this study, the authors examine by simulation, its application to in-situ patterning during materials growth. To understand the potential, it is important to study the surface processes resulting from the laser–matter interaction, which have a key influence on the resulting growth mechanisms. In this work, the intensity distribution and the laser–semiconductor interaction resulting from four-beam interference patterns are analysed by numerical simulations. In particular, the authors derive the time and spatially dependent thermal distribution along with the thermal-induced desorption and surface diffusion. The results provide a crucial understanding of the light-induced thermal profile and show that the surface temperature and the surface adatom kinetics can be controlled by multi-beam pulsed laser interference patterning due to photothermal reactions. The approach has potential as an in-situ technique for the fast and precise nanostructuring of semiconductor material surfaces.

Thermodynamic Processes on a Semiconductor Surface during In-Situ Multi-Beam Laser Interference Patterning

Thermodynamic Processes on a Semiconductor Surface during In-Situ Multi-Beam Laser Interference Patterning

Micro and nano dual-scale structures fabricated by amplitude modulation in multi-beam laser interference lithography

In this work, an effective method was presented to obtain a specific micro and nano dual-structures by amplitude modulation in multi-beam laser interference lithography (LIL). Moire effect was applied to generate the amplitude modulation. The specific intensity modulation patterns can be obtained by the control of the parameter settings of incident laser beams. Both the incident angle and azimuth angle asymmetric configurations can cause the amplitude modulation in the interference optic field and the modulation period is determined by the angle offset. A four-beam LIL system was set up to fabricate patterns on photoresist and verify the method. The experimental results are in good agreement with the theoretical analysis.

Bio-inspired hierarchical patterning of silicon by laser interference lithography.

This paper presents a facile approach for the rapid and maskless fabrication of hierarchical structures by multibeam laser interference. In the work, three- and four-beam laser interference lithographies were proposed to fabricate ordered multiscale surface structures instead of six or more beam interference with a complicated system setup. The pitch and shape of hierarchical structures can be controlled by adjusting the parameters of incident light. The experiment results have shown that the hierarchical anisotropy and isotropy surface structures can be fabricated by this method with the control of the parameters of each incident beam, which is in accordance with the theoretical analysis and computer simulations.

Selected laser methods for surface structuring of biocompatible diamond-like carbon layers

Laser based surface structuring methods are among the fastest growing techniques and displace other surface treatments for applications such as marking, change of topography and microstructure. Such changes may lead to controlled modification of material properties, including their biocompatibility. The paper presents two laser techniques — picosecond Direct Laser Writing (DLW) and multi-beam Direct Laser Interference Lithography (DLIL). The purpose of the research was to create different shapes and dimensions of 2D and 3D periodical microstructures on the surface of thin diamond like carbon (DLC) coatings on different substrates. Resulting structures were further tested to find the influence of laser processing on the interaction of created scaffolds with the living cells in the direction of improvement of their directional growth and adhesion. The use of two different patterning methods (DLW and DLIL) allowed creation of structures with periods ranging between sub-microns to tens of microns, with different pattern resolutions, shapes (linear, dotted, crossed, hierarchical) and depths. Preliminary analyses have shown the possibility of high degree of control and improvement in the directional growth of smooth muscle cells and the proliferation of the endothelial cells, cultivated on migration channels created at DLC layers.

An equivalent method of multi-beam laser interference lithography for 2D plasmonic crystals fabrication

We proposed an approach to fabricate two-dimensional (2D) plasmonic crystals based on equivalent multi-beam interference lithography. With a self-designed truncated hexagonal pyramid, three sub-wavelength structures were demonstrated and characterized, and the corresponding simulation was also carried out and well fitting. Further, the plasmonic Bloch waves (PBWs)–mediated fluorescence radiation was investigated and the wavelength-dependent fluorescence directional emission was observed. This work might provide a simple, flexible and low-cost way to achieve complex large-scale plasmonic crystals with nanoscale features for some practical applications, such as surface-enhanced Raman scattering (SERS) substrates, photovoltaic devices and biological chips.

Surface topography enhances differentiation of mesenchymal stem cells towards osteogenic and adipogenic lineages

Surface topography impacts on cell growth and differentiation, but it is not trivial to generate defined surface structures and to assess the relevance of specific topographic parameters. In this study, we have systematically compared in vitro differentiation of mesenchymal stem cells (MSCs) on a variety of groove/ridge structures. Micro- and nano-patterns were generated in polyimide using reactive ion etching or multi beam laser interference, respectively. These structures affected cell spreading and orientation of human MSCs, which was also reflected in focal adhesions morphology and size. Time-lapse demonstrated directed migration parallel to the nano-patterns. Overall, surface patterns clearly enhanced differentiation of MSCs towards specific lineages: 15 μm ridges increased adipogenic differentiation whereas 2 μm ridges enhanced osteogenic differentiation. Notably, nano-patterns with a periodicity of 650 nm increased differentiation towards both osteogenic and adipogenic lineages. However, in absence of differentiation media surface structures did neither induce differentiation, nor lineage-specific gene expression changes. Furthermore, nanostructures did not affect the YAP/TAZ complex, which is activated by substrate stiffness. Our results provide further insight into how structuring of tailored biomaterials and implant interfaces – e.g. by multi beam laser interference in sub-micrometer scale – do not induce differentiation of MSCs per se, but support their directed differentiation.

Fabrication of Periodic Microstructures on Nickel Template by Multi-Beam Laser Interference

Complex microstructures can be fabricated on nickel template directly by femtosecond laser. But the efficiency is low and much time is inevitable when large scale microstructures are fabricated. The multi-beam interference provides an effective method for fabrication of large scale microstructures. This paper mainly focuses on direct ablation of nickel template by four-beam interference and fabricating periodic microstructures by laser interference lithography. Experimental results show that submicron periodic stripes and column structures can be produced on the nickel template by laser interference, laying the foundation of making nickel molds for microfluidic chips.

Throughput comparison of multiexposure and multibeam laser interference lithography on nanopatterned sapphire substrate process

In this research, we describe a new approach, i.e., laser interference lithography (LIL), to fabricating pattern sapphire substrate (PSS) and nanopatterned sapphire substrate (NPSS). There are two ways to pattern hexagonal 2D arrays on sapphire by LIL: multiexposure LIL and multibeam LIL. In conclusion, the simulation results in this research verified that multibeam LIL has significantly better throughput than multiexposure LIL. The result also supports the advantages of a negative photoresist over a positive photoresist.

Formation and applications of periodic structures in transparent materials induced by single fs laser beam

In this paper, we present our recent research development on single fs laser beam induced periodic structures, i.e. nanovoid array, tilted grating structures, nanograting etc, and discuss the mechanisms and promising applications of the observed periodic structures. Periodic structures can be used as grating and lens etc. Usually they are prepared by point-by-point or line by line laser scanning and using multi-beam laser interference technique. However, periodic nanovoid array was observed in transparent materials along the propagation direction of single fs laser beam. (1) By adopting a physical model which combines the nonlinear propagation of fs laser pulses with the spherical aberration (SA) effect at the interface of two mediums of different refractive indices, reasonable agreements between the simulation results and the experimental results were obtained. By comparing the fluence distributions of the case with both SA and nonlinear effects included and the case with only consideration of SA, we suggest that SA, which results from the refractive index mismatch between air and fused silica glass, is the main reason for the formation of the self-organized void array. (2) We observed self-organized microgratings in the bulk SrTiO3 crystal by scanning the laser focus in the direction perpendicular to the laser propagation axis. The groove orientations of those gratings could be controlled by changing the irradiation pulse number per unit scanning length, which could be implemented either through adjusting the scanning velocity at a fixed pulse repetition rate or through varying the pulse repetition rate at a fixed scanning velocity. (3)

Low-cost micro-lens arrays fabricated by photosensitive sol–gel and multi-beam laser interference

In this paper, we introduce a low-cost approach for fabricating micro-lens arrays that is based on photosensitive sol–gel and multi-beam laser interference. UV photosensitive ZrO2 gel films are prepared with Zr(O(CH2)3CH3)4 and BzAcH as the precursor and chemical modifier, respectively. With UV laser irradiation via different dose, nonlinear photodecomposition occurs in this film. Large scale 2D micro lens arrays with the sizes of 830nm×830nm and 280nm×280nm are fabricated by four-beam laser interference. The surface profile modeling shows that the micro lens is plano convex lens, and the effective focal lengths are 812.0nm and 317.6nm, respectively.

多光束激光干涉光刻图样

多光束激光干涉光刻图样

Two different coercivity lattices in Co/Pd multilayers generated by single-pulse direct laser interference lithography

We report on magnetic structuring of Co/Pd multilayer films with strong perpendicular magnetic anisotropy by single-pulse direct laser interference lithography technique. Multibeam laser interference generates patterns of various types. The intense laser irradiation at interference maxima causes chemical intermixing at Co/Pd interfaces, leading to local changes in magnetic properties such as the creation of pinning centers and the reduction in the strength of magnetic anisotropy. We use magnetic force microscopy and Kerr microscopy to study the magnetization reversal processes in the patterned samples and find that the structures show three distinctly different behaviors depending on the intensity of the laser used for irradiation.

Inside Front Cover -Advanced Biomaterials 1/2009

The cover picture by Lasagni et. al shows two-dimensional periodic microstructures of polyethylene glycol diacrylate (PEG-DA) fabricated using nanosecond (top) and femtosecond (bellow) multibeam laser interference patterning (MLI). The periodic topography can be varied by simple control of the interference patterns as well as exposure dosages. Such structures with controlled topography are of relevant importance for applications in biomedical devices.

Fabrication of two-dimensional periodic TiO2 pillar arrays by multi-beam laser interference lithography

Two-dimensional (2D) periodic TiO2 pillar arrays, applicable to photonic crystals and micro-channels, were fabricated by direct patterning of a TiO2-organic hybrid material by multi-beam laser interference lithography and calcination of hybrid patterns. 2D periodic pillars of a TiO2– organic hybrid material were prepared by irra-diation with the interference pattern of femto-second laser beams and removal of the non- irradiated portions. Two types of periodic pillar arrays, standing pillars and top-gathering pillars (four pillars gathered at the top), were obtained, depending on laser irradiation conditions. After calcination of TiO2–organic hybrid pillars, TiO2 pillar arrays were obtained without collapse.

Fabrication of organic-inorganic hybrid patterns by lithography

Periodic patterns with submicrometer to micrometer repetitions are known to be applicable for various optical devices such as diffractive gratings and photonic crystal. In this paper, the periodic patterns of organic-inorganic hybrid materials have been fabricated by photolithography using UV and laser. The hybrid materials derived by the sol-gel method were composed of inorganic materials modified photosensitive organic groups. The photosensitive materials were irradiated periodically by UV light or multi-beam laser interference light, and periodic patterns were fabricated by removal of the unirradiated parts and rinse using the chemical solutions. The pillar sizes such as the height and the distance between neighboring pillars and kinds of the rinse liquids were controlled, resulting in the pillar patterns. Especially, new pillar patterns, in which the pillars are gathered at the top, were obtained by the capillary force between pillars during the drying of the rinse liquid. The interference light of femtosecond beams were irradiated for the TiO2-organic hybrid materials with high refractive index, and periodic patterns with submicrometer repetitions were fabricated. The patterns were controlled by the number of the beam, and various kinds of two- or three-dimensional periodic patterns were obtained.

Multi-step multi-beam laser interference patterning of three-dimensional photonic lattices

We present laser interference patterning of three-dimensional photonic lattice structures with three-step three-beam irradiation. In contrast to one-step four-beam interference patterning, the proposed method makes it possible to continuously tune the lattice constant and the photonic band gap without distortion of the lattice shape. We analytically show that all fourteen Bravais lattices are possible to be produced by choosing proper incident vectors of laser beams. A simple routine to seek the geometrical configuration of the incident beams for producing arbitrary Bravais lattices is shown. Furthermore, We experimentally demonstrate the fabrication of three-dimensional photonic lattices in the photoresist SU-8. Significant photonic band gap effects have been observed from the well-defined photonic lattices.

Periodic Structures of Organic-Titania Hybrid Materials Recorded by Multi-Beam Laser Interference Technique

Photosensitive organic-titania hybrid materials have been prepared from metal alkoxides and various organic ester compounds with \(C{=}C\) double bonds. The refractive index of the film increases with the decrease of the concentration of the organic ester compound, and the highest refractive index of 1.62 is obtained when 2-hydroxymethyl acrylate (HOA) is used as the organic ester and the molar ratio of HOA to Ti is 0.5. The material with the highest refractive index is exposed to femtosecond pulse using the multi-beam laser interference technique. After laser irradiation, the irradiated parts of the material are photopolymerized and periodic structures can be obtained by development of the unirradiated parts. In the case of laser irradiation of 120 μ J total energy for 5 min, the periodic structure obtained corresponds to 2D photonic crystal structure which is composed of two parts; the material with the highest refractive index and the air.

Multiphoton-induced periodic microstructures inside bulk azodye-doped polymers by multibeam laser interference

We report on multiphoton-induced periodic microstructures inside bulk polymers by multibeam interference of femtosecond laser pulses at a wavelength of 800 nm, which is out of the linear absorption range of the polymer sample. Two-dimensional structures and three-dimensional periodic microstructures were fabricated inside bulk azodye-doped polymethylmethacrylate by four-beam interference and five-beam interference, respectively. The Raman spectra measurements for the photomodified area of the sample before and after irradiation with the writing light showed that the periodic microstructures probably arose from photoinduced decomposition reaction of azodye molecules through multiphoton absorption.