Two-beam Interference Setup Research Articles

Multi-Scale Structuring of CoCrMo and AZ91D Magnesium Alloys Using Direct Laser Interference Patterning

In this work, the technique of Direct Laser Interference Patterning (DLIP) was used to fabricate micrometric structures at the surface of Cobalt-Chromium-Molybdenum and AZ91D magnesium alloys. Line-like patterns with spatial periods of 5 μm were textured using an ultra-short pulsed laser (10 ps pulse duration and 1064 nm wavelength) with a two-beam interference setup. The surface topography, morphology, and chemical modifications were analysed using Confocal Microscopy, Scanning Electron Microscopy, and Energy Dispersive Spectroscopy (EDS), respectively. Laser fluence and pulse overlap were varied to evaluate their influence on the final structure. Homogeneous structures were achieved for the CoCrMo alloy for every condition tested, with deeper structures (up to 0.85 μm) being achieved for higher energy levels (higher overlap and/or fluence). For high energy, sub-micrometric secondary structures, so-called LIPSS, could also be observed on the CoCrMo. The EDS analysis showed some oxidation after the laser texturing. Regarding the AZ91D alloy, deeper structures could be achieved (up to 2.5 μm), but more melting and oxidation was observed, forming spherical oxide particles. Nonetheless, these results bring new perspectives on the fabrication of microtextures on the surface of CoCrMo and AZ91D using DLIP.

Multi-scale textured PEEK surfaces obtained by direct laser interference patterning using IR ultra-short pulses

In this work, we aimed at getting the first insight into the influence of the laser processing parameters on the production of functional multi-scale PEEK surfaces using the Direct Laser Interference Patterning technology. An infrared ultra-short pulsed laser source (1064 nm, 10 ps) and a two-beam interference setup were used. The fabricated structures morphology was analyzed by Scanning Electron Microscopy and Confocal Microscopy. As a result, line-like structures with periodic spatial repetition (p) at two levels were produced: main structures with p = 5 µm and mean depth values up to ∼2.5 µm (aspect ratio of ∼0.5) and secondary structures, perpendicularly oriented relative to the main structures, formed at DLIP maxima position (top part of ridges) with p≈1 µm (LIPSS).

Measurement of the Pancharatnam–Berry phase in two-beam interference

Young’s dual-pinhole interference experiment with arbitrary fully correlated and polarized vector light fields leads to a Pancharatnam–Berry geometric phase that is related to the associated dynamical phase. We demonstrate theoretically and experimentally how the dynamical phase across the interference pattern can be deciphered from the total phase, thereby leaving only the geometric phase. Our results constitute the first genuine interferometric phase measurements that yield the Pancharatnam–Berry geometric phase in Young’s two-beam interference setup.

Prediction of Optimum Process Parameters Fabricated by Direct Laser Interference Patterning Based on Central Composite Design.

In this study, we report on the optimization of the direct laser interference patterning process by applying the design of experiments approach. The periodic line-like microstructures of a 8.50 µm spatial period were fabricated by a two-beam interference setup with nanosecond laser pulses, varying laser fluence, pulse overlap, and hatch distance. Central composite design with three factors and five levels was implemented to optimize the required number of experiments. The experimental and numerical results show the impact of various structuring process parameters on surface uniformity. The responses measured are the structure height, height error, and waviness of the pattern. An analysis of the microstructures on the patterned surface was conducted by confocal microscopy and scanning electron microscopy. A 3D-characterization method based on morphological filtering, which allows a holistic view of the surface properties, was applied, and a new qualification scheme for surface microstructures was introduced. Empirical models were also developed and validated for establishing relationships between process parameters and performance criteria. Multi-objective optimization was performed to achieve a minimal value of structure height errors and waviness.

Fabrication of hierarchical surface textures using multi-pulse direct laser interference patterning with nanosecond pulses

Abstract In this study, we report on the one-step fabrication of hierarchical microstructures on stainless steel substrates using multi-pulse Direct Laser Interference Patterning. The complex structures are produced using a two-beam interference setup with nanosecond laser pulses. The effect of laser fluence and number of pulses on the formation of multi-scale microstructures is systematically investigated. The resulting surface structures are characterized by scanning electron microscopy and white light interference microscopy. It was observed that at low laser fluence, the periodic microstructures remain defined and grow in height above the initial surface, independent on the number of pulses. For higher laser fluences as well as larger number of pulses, the structures adopt a crater-like morphology including a periodic line-like structure.

One-step fabrication of asymmetric saw-tooth-like surface structures on stainless steel using Direct Laser Interference Patterning

We report about the fabrication of asymmetrical periodic arrays on stainless steel by means of Direct Laser Interference Patterning. The fabrication strategy consists in irradiating the surface of the material under a certain inclination angle using a two-beam interference setup equipped with a pulsed picosecond laser system (70 ps) operating at a wavelength of 1064 nm. In particular, for tilting angles higher than 30°, well-defined saw-tooth like geometries could be produced. Due to the ultra-short duration of the laser pulses, also Laser Induced Periodic Surfaces Structures are fabricated, which create hierarchical morphologies similar to the one present in nature.

Fabrication and characterization of diffraction gratings in ophthalmic polymers by using UV direct laser interference patterning

The fabrication of diffractive elements in ophthalmic polymers to induce refractive index changes which may be applied for refractive correction is of great interest in the fields of Optics and Ophthalmology. In this work, poly-hydroxyethyl-methacrylate and silicone hydrogel polymers used as soft contact lenses were structured with linear periodic patterns by means of Direct Laser Interference Patterning (DLIP). As the laser source, a Q-switched laser system emitting 10 ns pulses at a wavelength of 266 nm was used to generate the periodic modulation on the surface of the polymer materials. The experiments were carried out employing a two-beam interference setup, studying the features of the laser processed areas as a function of both the laser fluence and the interference period. The topography of the structured areas was investigated using optical confocal microscopy. Compositional and structural modifications on the materials were studied by means of micro-Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Finally, periodic patterns were characterized through diffractive techniques under illumination of a continuous-wave 632.8 nm He-Ne laser to determine the diffractive properties of the DLIP periodic patterns and the refractive index change induced by the laser processing.

Realizing Large-Area Arrays of Semiconducting Fullerene Nanostructures with Direct Laser Interference Patterning.

We present a laser interference patterning method for the facile fabrication of large-area and high-contrast arrays of semiconducting fullerene nanostructures, which does not rely on a tedious application of sacrificial photoresists or photomasks. A solution-deposited phenyl-C61-butyric acid methyl ester (PCBM) fullerene thin film is exposed to a spatially modulated illumination intensity, as realized by a two-beam laser interference. The PCBM molecules exposed to strong intensity are photochemically transformed into a low-solubility dimeric state, so that the nontransformed PCBM molecules can be selectively removed in a subsequent solution-based development step. Following brief exposure to green laser light (λ = 532 nm, t = 5 s, p = 0.17 W cm-2) in the designed two-beam interference setup, and a 1 min development in a tuned acetone-chloroform solution, we realize well-defined and ordered PCBM nanostripe patterns with a fwhm line width of ∼200 nm and a repetition rate of ∼2.900 lines mm-1 over a large area of 1 cm2. We demonstrate that a desired high contrast is effectuated because the initial PCBM-dimer transformation rate is dependent on the square of the illumination intensity. The semiconducting functionality of the patterned fullerene is verified in a field-effect transistor experiment, where a typical PCBM nanostripe featured an electron mobility of 5.3 × 10-3 cm2 V-1 s-1 and an on/off ratio of 3 × 103.

Identity authentication based on two-beam interference and nonlinear correlation

In this paper, a new approach to identity authentication is proposed, which takes advantage of the two-beam interference setup and the nonlinear correlation technique. According to the traditional two-beam interference encryption/decryption structure, we design a modified iterative phase retrieval algorithm (MIPRA), which takes the random binary amplitudes as the constraints at the input plane to encode different images (standard reference images) into a set of sparse phase distributions. In the MIPRA, a given random phase distribution serves as a system lock, and it is placed at one of the arms of the two-beam interference setup and keeps unchanged in the whole iterative phase retrieval algorithm but equivalently provides a fixed shifting vector toward the output complex amplitude field. While the peak-to-correlation value (between the output intensity and the original image) reaches a presetting threshold value, or the iterative numer of time reaches a presetting maximum value, the MIPRA stops. Here, the phase lock is assumed to be the same for all the users and thus it is placed and fixed in the system, while the calculated phase distributions vary from the MIPRA to different binary constraints, which are related to different users. Meanwhile, we also study an extension version of the proposed method. By using a superposition multiplexing technique and a nonlinear correlation technique, we can realize a function of hierarchical authentication for various kinds of users through a similar but more smart decision strategy. For example, we adopt the MIPRA four times with different constraints (random binary amplitude distribution) to obtain four phase distributions, the sum of them will be regarded as a final phase key and is designed to the user with the highest privilege. He is then able to pass all the authentication process for each standard reference image with his multiplexed phase key, that is to say, there are obvious peaks in all the nonlinear correlation maps between all the output images and the corresponding standard reference images. In a similar way, the user with the lowest privilege can only pass one authentication process. Compared with the previous identity authentication methods in the optical security area, the phase key for each user, no matter what level he belongs to, is easy to be stored and transmitted because its distinguishing feature of sparsity. It is worthwhile to note that the cross-talk between different output images are very low and will has no effect on the authentication decision since we deliberately assemble all the binary distributions, which act as constraints at the input plane in the MIPRA. Moreover, the output results are all noise-like distributions, which makes it nearly impossible for any potential intruders to find any clues of the original standard reference images. However, on the other hand, with the nonlinear correlation technique, we can easily extract enough information from these noise-like output results to authorize any users, usually we can obtain an obvious peak at the center of the correlation results but there is no peak if we adopt the traditional correlation algorithms. This feature helps reduce the risk of information leakage, thereby providing an additional protection layer. Also, weinvestigate the robustness properties by taking the sparsity ratio, Gaussian noise, and shear/occluded attack into consideration. Some previous tests alsoindicated that our scheme can resist the attack employing incorrect random phase keys. Theoretical analysis and a series simulation results are provided to verify the feasibility and effectiveness of the proposed scheme.

Surface Characterization of Carbon Fiber Polymer Composites and Aluminum Alloys After Laser Interference Structuring

The increasing use of carbon fiber-reinforced polymer matrix composites (CFPC) and aluminum alloys as lightweight materials in the automotive and aerospace industries demands enhanced surface preparation and control of surface morphology prior to joining. In this study, surfaces of both composite and aluminum were prepared for joining using an Nd:YAG laser in a two-beam interference setup, enabling the (1) structuring of the AL 5182 surface, (2) removal of the resin layer on top of carbon fibers, and (3) structuring of the carbon fibers. CFPC specimens of T700S carbon fiber, Prepreg—T83 epoxy, 5 ply thick, 0°/90° plaques were used. The effects of laser fluence, scanning speed, and number of shots-per-spot were investigated on the removal rate of the resin without an excessive damage of the fibers. Optical micrographs, 3D imaging, and scanning electron microscope imaging were used to study the effect of the laser processing on the surface morphology. It was found that an effective resin ablation and a low density of broken fibers for CFPC specimens was attained using laser fluences of 1–2 J/cm2 and number of 2–4 pulses per spot. A relatively large area of periodic line structures due to energy interference were formed on the aluminum surface at laser fluences of 12 J/cm2 and number of 4–6 pulses per spot.

Photorefractive properties of iron-doped lithium tantalate crystals

Summary form only given. We have grown congruent iron-doped LiTaO/sub 3/ crystals with six different iron concentrations. Photorefractive properties are studied by means of a two-beam interference setup. Holograms are recorded and erased with ordinarily polarized light of different wavelengths of an Ar-ion laser.

Quasi-collinear and partially degenerate four-wave mixing: An alternative explanation of the phase-conjugation property of backward stimulated scattering

A quasi-collinear and partially degenerate four-wave mixing model is proposed to explain the optical phase-conjugation property of various types of stimulated backscattering. According to this model, after passing through a phase-disturbed medium or an aberration plate, the input pump beam can be resolved into two portions: a stronger undisturbed regular portion and a weaker phase-disturbed irregular portion. These two portions interfere with each other and create a volume holographic grating in the pumped region of the scattering medium. Only the stronger undisturbed portion of the pump field can excite an initial backward stimulated scattering beam with a regular wavefront. When the latter (as a reading beam) passes through the induced holographic grating, a diffracted wave will be created and then amplified together with the reading beam. A rigorous mathematical analysis shows that under certain conditions the combination of these two portions (the reading wave and the diffracted wave) of the backward stimulated scattering can be an approximate phase-conjugate field of the input pump field. The major theoretical conclusions are basically supported by the experimental results based on a specially designed two-beam interference setup.

Optical and Photorefractive Characterization of BTO Crystals Doped with Cd, Ca, Ga, and V

Single crystals of Bi12TiO20 (BTO) are grown by a modified Czochralski technique. Doping with cadmium, calcium, gallium, and vanadium is performed by adding corresponding oxides to the melt. Optical parameters like refractive index, optical absorption, optical activity, light induced absorption, electrooptic coefficient, and photoconductivity are determined. Photorefractive properties of the samples are characterized with the help of a conventional two-beam interference setup. Diffraction efficiency and decay time constant of elementary holograms are determined. The influence of the utilized dopands is discussed.