Four-beam Laser Research Articles

Three-Dimensional Nano-displacement Measurement by Four-Beam Laser Interferometry

A 3D nano-displacement measurement method, where the difference in phase between the beams in a four-beam laser interference is changed, is proposed. Simulation results demonstrate that the variation of phase difference causes the deviation of the interference pattern in the laser interference system. Based on this theory, we design and build a four-beam laser interference system. The corner cube prism in the optical path is shifted, and the phase of the beam is changed by applying different voltages to a piezoelectric stage. The phase difference is obtained by analyzing the lattice pattern with subpixel precision, and then the displacement is determined by correlation operation. The experimental measurement results are consistent with the theoretical analysis, thereby verifying the feasibility of this measurement method.

Wettability control of polymeric microstructures replicated from laser-patterned stamps

In this study, two-step approaches to fabricate periodic microstructures on polyethylene terephthalate (PET) and poly(methyl methacrylate) (PMMA) substrates are presented to control the wettability of polymeric surfaces. Micropillar arrays with periods between 1.6 and 4.6 µm are patterned by plate-to-plate hot embossing using chromium stamps structured by four-beam Direct Laser Interference Patterning (DLIP). By varying the laser parameters, the shape, spatial period, and structure height of the laser-induced topography on Cr stamps are controlled. After that, the wettability properties, namely the static, advancing/receding contact angles (CAs), and contact angle hysteresis were characterized on the patterned PET and PMMA surfaces. The results indicate that the micropillar arrays induced a hydrophobic state in both polymers with CAs up to 140° in the case of PET, without modifying the surface chemistry. However, the structured surfaces show high adhesion to water, as the droplets stick to the surfaces and do not roll down even upon turning the substrates upside down. To investigate the wetting state on the structured polymers, theoretical CAs predicted by Wenzel and Cassie-Baxter models for selected structured samples with different topographical characteristics are also calculated and compared with the experimental data.

Formation of laterally ordered quantum dot molecules by in situ nanosecond laser interference

We demonstrate the growth and surface characterization of laterally ordered arrays of InAs quantum dot molecules (QDMs) on GaAs (100) substrates produced by a combination of in situ interferometric nanopatterning and molecular beam epitaxy growth. Four-beam ultraviolet laser interference is applied during the growth process resulting in the formation of quasi two-dimensional islands due to localized surface diffusion. With further InAs deposition, the edges of the islands are observed to act as preferential sites for the nucleation of InAs quantum dots. Well-ordered square arrays of lateral QDMs with a period of 300 nm and site occupancy ranging from single dot up to hexa-molecules are obtained by varying the InAs coverage from 1.55 ML to 1.75 ML.

Effect of polarization mode on interference processing by dual-injection four-beam laser

The four-beam laser interference processing technology has obtained good theoretical and experimental progress in the preparation of drug-loaded microstructures of coronary stent, and further improving the effect of processing has become a hotspot in recent research. This paper analyzes and calculates the light intensity distribution under different polarization combinations of four-beam lasers. Through modeling and simulation, the interference processes and results under three different polarization modes were simulated, and the higher interference light intensity was obtained in TE-TE-TM-TM mode; based on this, a dual-injection four-beam interference lithography system was built, and interference processing experiments were performed on silicon wafer. The laser wavelength used is 1064 nm, the energy of the four lasers is 97 mJ, 80 mJ, 97 mJ, and 78 mJ, all four beams have an incident angle of 45 degrees, the azimuth angles are 0 degrees, 90 degrees, 180° and 270°, the pulse width is 8.2 ns, the repetition frequency is 10 Hz, and the exposure time is 60 s. In the experiment, the microarray structure of the hole array with a period of 1.073 μm was obtained, which is in line with the simulation results. The work in this paper shows that when the combined polarization mode is TE-TE-TM-TM, the dual-injection four-beam interference processing system can achieve the best processing effect.

Precise Arrays of Epitaxial Quantum Dots Nucleated by In Situ Laser Interference for Quantum Information Technology Applications.

Precisely ordered arrays of InAs quantum dots are formed on a nanoisland-structured GaAs (100) surface using in situ laser interference during self-assembled molecular beam epitaxial growth. Nanoislands induced by single-pulse four-beam laser interference act as preferential nucleation sites for InAs quantum dots and result in site occupation dependent on the size of nanoislands, the InAs coverage, and the laser parameters. By optimizing the growth and interference conditions, regular dense ordering of single dots was obtained for the first time using this in situ noninvasive approach. The photoluminescence spectra of the resulting quantum dot arrays with a period of 300 nm show good optical quality and uniformity. This technique paves the way for the rapid large-scale fabrication of arrays of single dots to enable quantum information technology device platforms.

Preparation of miRNA137 biomimetic coated coronary stent by dual-injection four-beam laser interference

In recent years, miRNA137 has shown great potential in inhibiting postoperative restenosis. In this paper, a mutual injection dual-output solid-state laser was used as the light source to construct a four-beam interferometric processing system to perform micro-nano processing on the surface of the metal coronary stent, which provides a good substrate for loading the miRNA137 onto the surface of the stent. The laser used in the experiment has a working wavelength of 1064 nm, and the energy of the two lasers is 183 mJ and 181 mJ, the energy of the four laser beams obtained by beam splitters is 97mJ, 83mJ, 95mJ and 82mJ respectively, the angle between the beams is 90 degrees and the exposure time is 60 s. When the incident angle is 14.52 degrees, a bionic micro/nano structure with a period of 3.077 μm is obtained. According to the preliminary comparative test, the structed stent with a period of 3.077 μm has stronger adhesion property and longer drug release period to miRNA137 compared with the period of 1.063 μm and 5.082 μm.

Demonstration of 2.5 J, 10 Hz, nanosecond laser beam combination system based on non-collinear Brillouin amplification.

We demonstrated a four-beam combined laser system based on Brillouin amplification with a nanosecond output of 2.5 J at a 10 Hz repetition rate. We used simulations and experiments to assess factors affecting the energy extraction efficiency of non-collinear Brillouin amplification. Our results indicate that higher efficiency can be achieved by adding pump beams to the Brillouin amplification process, which enhances optical field intensity and interaction strength. To the best of our knowledge, this is the first demonstration of a multi-beam combination system based on Brillouin amplification with an output of joule level energy, high peak power and nanosecond pulses in 10Hz repetitive operation.

In-situ laser nano-patterning for ordered InAs/GaAs(001) quantum dot growth

A study of in-situ laser interference nano-patterning on InGaAs wetting layers was carried out during InAs/GaAs (001) quantum dot molecular beam epitaxy growth. Periodic nano-islands with heights of a few atomic layers were obtained via four-beam laser interference irradiation on the InGaAs wetting layer at an InAs coverage of 0.9 monolayer. The quantum dots nucleated preferentially at edges of nano-islands upon subsequent deposition of InAs on the patterned surface. When the nano-islands are sufficiently small, the patterned substrate could be spontaneously re-flattened and an ordered quantum dot array could be produced on the smooth surface. This letter discusses the mechanisms of nano-patterning and ordered quantum dot nucleation in detail. This study provides a potential technique leading to site-controlled, high-quality quantum dot fabrication.

高度方向性多光束有机激光

The advantages of organic lasers with DFB distributed feedback structures have attracted much attention, however, there are few reports on the principle of multi-beam organic lasers using high-order Bragg feedback. Different from single-waveguide or single-beam lasers implemented by low-order Bragg feedback in the past, high-order Bragg feedback is introduced into a planar organic semiconductor waveguide to produce red and blue multi-beam organic lasers in this paper. Using a fourth-order Bragg feedback and PVK:DCJTI film, a three-beam red laser is realized with an exit angle of ±53° and 0.5°. A four-beam blue laser is implemented using a fifth-order Bragg feedback and PS:DSA-ph film with exit angles of ±18° and ±75°. The relationship between higher-order Bragg grating feedback and device characteristics is studied by combination of plane waveguide and grating coupling. The results show that the theoretically calculated beam coupling angle is consistent with the actual test, which provides guidance for the design of multi-beam organic laser devices to some extent.

Target reconstruction algorithm for four-beam sheared coherent imaging

Sheared-beam imaging, which is a nonconventional coherent laser imaging technique, can be used to better solve the problem of taking pictures with high resolution for remote targets through turbulent medium than conventional optical methods. In the previous research on this technique, a target was illuminated by three coherent laser beams that were laterally arranged at the transmitter plane into an L pattern. In order to obtain a high quality image, a series of time-varying scattered signals is collected to reconstruct speckled images of the same object. To overcome atmospheric turbulence, multiple sets of three-beam laser should be emitted, which increases data acquisition time. In this paper, aiming at the quasi real-time problem of conventional sheared beam imaging technique, we use four-beam laser with rectangular distribution instead of the traditional L type sheared three-beam laser to illuminate the target. According to this, we propose a target reconstruction algorithm for four-beam sheared coherent imaging to reconstruct four target images simultaneously in one measurement, which can acquire high quality images by reducing the amount of measurement and the speckle noise. Meanwhile, it can greatly reduce the amount of beam switching in multi-group emission and improve the imaging efficiency. Firstly, the principle of the four-beam sheared coherent imaging technique is deduced. Secondly, in the algorithm, the speckle amplitude and phase difference frames can be extracted accurately by searching for the accurate positions of the beat frequency components. Based on the speckle phase difference frames, four sets of wavefront phases can be demodulated by the least squares method, and wavefront amplitude can be obtained by algebraic operation of speckle amplitude. The reconstructed wavefront is used for inverse Fourier transform to yield a two-dimensional image. A series of speckled images is averaged to form an incoherent image. Finally, the validity of the proposed technique is verified by simulations. From the simulation results, the image quality of the proposed method is better than that of the traditional method in the same amount of measurement. Furthermore, on the premise of the same image quality, the data acquisition amount of the proposed method is 2-3 times as large as that of the traditional method. In other words, compared with that of the traditional method, the data acquisition time of the proposed method is reduced at least by half and the algorithm processing time is less. It can be concluded that the proposed imaging technique can not only improve the efficiency of target reconstruction, but also present a better way of imaging the remote moving targets.

Preparation of the micro/nano structures of the biomimetic coating stent for loading MiRNA126 by four-beam laser interference

We demonstrated the preparation of drug loading micro structures on the surface of metal coronary stent by using laser interference and provide a good substrate for the next step by using the method of miRNA-126 for the first time to our knowledge. Compared with the drug used in the existing drug eluting stent, miRNA-126 has a better effect on promoting the differentiation of vascular endothelial cells, inhibiting the inflammatory reaction and the proliferation of smooth muscle cells. The laser wavelength is 1064nm, the single pulse energy is 2J, the pulse width is 8ns and the exposure time is 80s. When the incident angle is 2.8°, between beam angle is 90°, we got the bionic micro nano structure witch cycle is 10.21μm. Different cycles can be obtained by changing the angle of incidence and the angle between the laser beam, After a preliminary comparison test, the cycle 10.21μm bracket micro nano structure is better than cycle 5.077μm and 20.9μm in the assembly adhesion force and loading capacity.

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.

Periodic structures fabricated by nanosecond laser four-beam interference ablation

Periodic micro/nano-structure has been playing an important role in microelectronics, microfluidics, micro/nano-optics. There are many technologies that have been proposed for structure manufacture, for example, photolithography, electron beam etching technique, nanoimprint technology. Although these technologies have their advantages, it is troubled by template production, corrosion solution and material choices. Multi-beam interference is one of the common technologies for fabrication of periodic structures as sacrificial layer. It is widely used for its easy setup, quick, and low cost capacities. Laser processing has the advantages of direct writing by light-absorbing under high energy density of pulsed laser of low costs, high quality, fine precision, non-flat three dimensional fabrication ability in transparent medium. Herein, based on principle of interference lithography especially four-beam interference and laser ablation, we proposed one step method of fabrication of large-area mocro/nano-structures by multiple beam laser interference ablation technology. As we all know, light intensity would be redistributed and represent periodic strong and weak variation. Quanta-Ray Nd:YAG Laser of wavelength 355 nm, repetition of 10 Hz and pulse duration of 10 ns was used for laser interference ablation with maximum power 1100 mW and diameter of 10 mm. Area under high light intensity above the threshold will be ablated and removed, while area under low light intensity below the threshold will be left. Thus with this periodic intensity distribution in multiple beam interference and the ablation mechanism, two-dimensional periodic structures in large area can be fabricated maskless on zinc sulfide (ZnS) surface in one step. Additionally, the experiment is in normal atmosphere and donnot need vacuum, which makes it easy and low cost. Structure with period of 3 μm at incident angle of 4.8° was chosen for example to investigate the transition of structure type, as well as the morphology evolution with exposure time in detail. While the incident angle of any beam is slightly changed, the two-dimensional distribution will break into two types, both of which have its own distribution. At the same time, these two types are distributed periodically. In our experiment, periodic holes and pillars were fabricated repeatedly on ZnS surface in the interference ablated area with a larger period about 74 μm. Periodic holes were of period 3 μm while pillars were of period 3 μm 1 / 2 . Distribution directions of pillars were 45° titled with that of holes. Further, the phenomenon of phase shift was studied by adjusting the incident angle of one beam in theory, which explained the experiment results well. At last, according to our study in recent years, the opportunity and challenge of multiple-beam interference ablation technology was discussed in this article. We are believed this interference ablation technology will be taking an important role in hard material processing, two dimensional periodic and quasi-periodic structure fabrication, OLED, solar cells and many more potential micro and nanotechnology regions.

Effects of laser fluence on silicon modification by four-beam laser interference

This paper discusses the effects of laser fluence on silicon modification by four-beam laser interference. In this work, four-beam laser interference was used to pattern single crystal silicon wafers for the fabrication of surface structures, and the number of laser pulses was applied to the process in air. By controlling the parameters of laser irradiation, different shapes of silicon structures were fabricated. The results were obtained with the single laser fluence of 354 mJ/cm2, 495 mJ/cm2, and 637 mJ/cm2, the pulse repetition rate of 10 Hz, the laser exposure pulses of 30, 100, and 300, the laser wavelength of 1064 nm, and the pulse duration of 7–9 ns. The effects of the heat transfer and the radiation of laser interference plasma on silicon wafer surfaces were investigated. The equations of heat flow and radiation effects of laser plasma of interfering patterns in a four-beam laser interference distribution were proposed to describe their impacts on silicon wafer surfaces. The experimental results have shown that the laser fluence has to be properly selected for the fabrication of well-defined surface structures in a four-beam laser interference process. Laser interference patterns can directly fabricate different shape structures for their corresponding applications.

Periodic nanostructures fabricated on GaAs surface by UV pulsed laser interference

In this paper, periodic nanostructures were fabricated on GaAs wafers by four-beam UV pulsed laser interference patterning. Significant different results were observed on epi-ready and homo-epitaxial GaAs substrate surfaces, which suggests GaAs oxide layer has an important effect on pulsed laser irradiation process. In the case of two-pulse patterning, a noticeable morphology transformation induced by the second pulse was observed on homo-epitaxial GaAs substrate. Based on photo-thermal mode, temperature distribution on sample surface as a function of time and position was calculated by solving the heat diffusion equations.

Bactericidal activity of titanium dioxide ultraviolet-induced films

TiO2 films are used as a self-sterilization surface due to their property to form reactive oxygen species (ROS) when irradiated with ultraviolet light. These ROS attack bacteria and kill them. We present a new way to enhance the bactericidal activity of TiO2-films: formation of nanopores on the surface by four-beam high-power laser irradiation. Such surfaces have significantly higher antibacterial activity as compared to conventional TiO2 surfaces after 15 and 60min of UV irradiation. Study of the bacterial cell morphology by atomic force microscopy after 60min irradiation showed that Staphylococcus aureus 956 and Escherichia coli 321–5 undergo significant morphological changes. S. aureus assume atypical elongated shapes after UV treatment alone and swollen forms with protrusions after UV treatment on TiO2 surface. E. coli exhibit oval or round forms after UV treatment alone, and round forms with small protrusions, and destroyed cells after incubation under UV on the TiO2 film.

Determination of beam incidence conditions based on the analysis of laser interference patterns

Beam incidence conditions in the formation of two-, three- and four-beam laser interference patterns are presented and studied in this paper. In a laser interference lithography (LIL) process, it is of importance to determine and control beam incidence conditions based on the analysis of laser interference patterns for system calibration as any slight change of incident angles or intensities of beams will introduce significant variations of periods and contrasts of interference patterns. In this work, interference patterns were captured by a He–Ne laser interference system under different incidence conditions, the pattern period measurement was achieved by cross-correlation with, and the pattern contrast was calculated by image processing. Subsequently, the incident angles and intensities of beams were determined based on the analysis of spatial distributions of interfering beams. As a consequence, the relationship between the beam incidence conditions and interference patterns is revealed. The proposed method is useful for the calibration of LIL processes and for reverse engineering applications.

Effects of azimuthal angles on laser interference lithography.

This paper discusses the effects of azimuthal angles on two-, three-, and four-beam laser interference. In two- or three-beam laser interference, periodic surface structures of lines or dots were obtained. In four-beam laser interference with the polarization mode of TE-TM-TE-TM, the modulation in a particular direction was formed and calculated. In the work, a He-Ne laser system was used to simulate two-, three-, and four-beam laser interference, and the interference pattern was detected by a CCD. A high-power Nd:YAG laser interference lithography system was set up to pattern silicon wafers. In the experiments, one azimuthal angle was changed every time to form interference patterns when polarization states were fixed and incident angles were equal. The experimental results have shown that the azimuthal angle affects the periods and feature sizes of the interference patterns and the fabricated surface structures, which are in accordance with the theoretical and computer simulation results.

Both antireflection and superhydrophobicity structures achieved by direct laser interference nanomanufacturing

Inspired by nature, a number of techniques have been developed to fabricate the bionic structures of lotus leaves and moth eyes in order to realize the extraordinary functions of self-cleaning and antireflection. Compared with the existing technologies, we present a straightforward method to fabricate well-defined micro and nano artificial bio-structures in this work. The proposed method of direct laser interference nanomanufacturing (DLIN) takes a significant advantage of high efficiency as only a single technological procedure is needed without pretreatment, mask, and pattern transfer processes. Meanwhile, the corresponding structures show both antireflection and superhydrophobicity properties simultaneously. The developed four-beam nanosecond laser interference system configuring the TE-TE-TE-TE and TE-TE-TE-TM polarization modes was set up to generate periodic micro cone and hole structures with a huge number of nano features on the surface. The theoretical and experimental results have shown that the periodic microcone structure exhibits excellent properties with both a high contact angle (CA = 156.3°) and low omnidirectional reflectance (5.9–15.4%). Thus, DLIN is a novel and promising method suitable for mass production of self-cleaning and antireflection surface structures.

Superhydrophobic dual micro- and nanostructures fabricated by direct laser interference lithography

A method for the fabrication of highly ordered superhydrophobic dual micro- and nanostructures on silicon by direct laser interference lithography (LIL) is presented. The method offers its innovation that the superhydrophobic dual micro- and nanostructures can be fabricated directly by controlling the process of four-beam laser interference and the use of hydrofluoric acid (HF) to wipe off the silica generated during the process. Different laser fluences, exposure durations, and cleanout times have been investigated to obtain the optimum value of the contact angle (CA). The superhydrophobic surface with the CA of 153.2 deg was achieved after exposure of 60 s and immersion in HF with a concentration of 5% for 3 min. Compared with other approaches, it is a facile and efficient method with its significant feature for the macroscale fabrication of highly ordered superhydrophobic dual micro- and nanostructures on silicon.