Rapid and flexible laser marking and engraving of tilted and curved surfaces

We present a novel method for rapid and flexible laser marking and engraving of tilted, curved and freeform work-piece surfaces. The method is based on integrating a three-dimensional (3D) laser measurement system into a 3D laser marking system. We use the same laser source and optics for measurement and processing with a minimum of additional hardware components. A low power CW laser regime is used to measure the 3D shape of a work-piece surface while a high-peak power-pulsed laser regime is used for processing. The acquired 3D surface data are used to determine the 3D trajectory of the processing beam focus. Neither the 3D shape of the work-piece nor its orientation needs to be known in advance as long as the processed surface lies within the working range of the 3D laser processing system. This eliminates the need for exact work-piece positioning before processing and substantially improves processing flexibility (allowing, e.g. variations in work-piece shape or/and orientation from mark to mark). This paper discusses key issues concerning an implementation of the method and presents typical examples of markings and engravings, which demonstrate the advantages of the method with respect to the existing industrial 2D and 3D laser marking and engraving methods. The method can also be applied to flexible laser structuring and microprocessing of curved surfaces.     

Atomic force microscopy of the mirror cleavage surface of defect TGS crystals

The nanorelief of the mirror cleavage surface of triglycine sulfate crystals with various defect densities has been studied. Typical nanorelief features of both defect and clean (without artificial impurity) crystals are two-dimensional rounded bumps (dips) of equal height (depth) of about half the lattice parameter and sub-micrometer lateral sizes. The density, lateral size, and scatter of such 2D structures are several times larger for defect crystals than for clean ones. The correlation between the crystal defect density and the density and lateral size of 2D structures on the cleavage surface has been revealed. Conclusions are made about the defect origin of the typical nanorelief on the mirror cleavage.     

Calculation algorithm of high-precision two-dimensional broadband laser warning parameters北大核心CSCD

High precision grating diffraction laser warning system is a photoelectric countermeasure equipment to judge and locate the incoming laser function. In order to improve the positioning accuracy, an improved algorithm for calculating and fitting the calculation parameters of the spot center was proposed. Firstly, the laser spot was preprocessed, and the center coordinates of the connected area were obtained by using the improved connected area marking algorithm and spot center extraction algorithm. Secondly, the azimuth angle and pitch angle were set, the images were collected and the spot center was calculated, and the pixel horizontal and vertical coordinates in x and y direction as well as fitting surfaces of laser parameters were fitted, so as to judge the azimuth angle, pitch angle and wavelength of the incoming laser. Finally, the improved connected area marking algorithm, spot center extraction algorithm and parameter fitting calculation results were compared with the traditional algorithm. The experimental results show that the pitch angle error between the fitting calculation results and the real data is less than 0.4°, and the azimuth angle error is less than 0.2°, which greatly improves the accuracy of laser direction recognition. Copyright ©2022 Journal of Applied Optics. All rights reserved.     

Effect of surface on phase modulation of light in a nematic layer

The nanorelief of orienting surfaces in a nematic layer is studied experimentally. The initial inclination angle of the director and the phase retardation of light in the crystal are determined, and the director reorientation dynamics in the crystal under SB deformation in an electric field is analyzed. It is shown that a thin layer of amorphous hydrogenated carbon (a-C: H) deposited on a GeO monoxide layer with an anisotropic nanorelief produced by the inclined deposition method smoothens the surface topography without changing the surface structure. Modification of the structure and physicochemical properties of the GeO surface alters the conditions of the anisotropic-elastic interaction at the interface with the liquid crystal, as evidenced by an increase in the S-effect threshold and a decrease in the initial inclination of the director from 22° (on the GeO surface) to 0–6°. Strong influence of the surface nanostructure on the dynamics of the director reorientation in the electric field and on the phase modulation of light is experimentally demonstrated. It is shown that the phase retardation of light in the GeO layer covered by an a-C: H film is twice as large as in the layer of the same thickness with a virgin surface.     

Studies on CO2 laser marking

The nature of CO₂ laser marking was studied with a view to putting these lasers to practical use in the semiconductor industry. The marking is found to be due to surface spattering rather than burning, which is the main factor in YAG laser marking. The visibility greatly increases by the application of a surface treatment such as marker ink, varnish or poster color. The CO₂ laser may therefore be used in place of the YAG laser, now widely used for marking, with some merits: CO₂ laser marking is cheaper and faster, and in addition there is no danger of injury from irradiating laser light.     

Laser marking of a laminated surface characterized by an optodynamic method

Marking plain surfaces using laser ablation is widely used in a serial production. However, during a laser marking of small laminated surfaces, a problem arises as a consequence of the gaps between the laminations; this tends to decrease the efficiency of the process. Therefore, a real-time measuring method that can be implemented in an industrial system for laser processing is required. In this contribution, we describe an optodynamic method for the on-line characterization of pulsed-laser marking of a laminated surface. The processing-laser beam generates an optodynamic response, i.e., the shock waves, which then spread into the surrounding gas. By using a laser-beam-deflection probe, the analysis of the obtained signals indirectly enables the real-time monitoring of the surface structure. Evaluation of the results obtained by our on-line measuring method is made by two techniques: non-destructive microscopy with extended depth of field and destructive cross-section measurements with optical microscopy. The performed experiments demonstrate that the established experimental system can simultaneously detect the changes in the laser-marking process. Furthermore, it can provide the position and the size of a gap as well as the orientation and the inclination of the samples.     

Correction of field distortion of laser marking systems using surface compensation function

Laser scanning systems are extensively applied in laser marking, laser printers, laser projection, and laser coding. They represent a very mature technique in the marking industry, and the galvanometric scanning systems are usually adopted in the laser marking system. Although the galvanometric scanning system usually increases the marking speed, it is usually accompanied by field distortion. The paper gives a correction method for the field distortion of a laser marking system, which, using the surface curve fitting function, corrected the control system of the scanning system. The field distortion errors of the laser marking system are corrected by the surface compensation function, which, using the surface curve fitting method, obtained the corrected position of laser spots. The results in this paper indicate that field-distortion errors of laser marking systems are effectively corrected by the surface compensation function. Moreover, the compensation method would be widely adopted to increase the accuracy of most two-dimensional machine systems, such as XY table, etc.     

Efficient speckle-free laser marking using a spatial light modulator

An approach for laser marking surfaces using a liquid–crystal-based spatial light modulator (LC-SLM) for beam patterning and manipulation is presented, designed to avoid the speckle interference problem which is a typical drawback of current SLM-based laser marking processes. In our approach, the LC-SLM is used to generate complex two-dimensional micropatterns (e.g., 20 × 20 datamatrices) with overall dimensions of < 320 by 320 μm. The micropatterns are generated in a series of 16 steps, using a Fresnel zone lens (FZL) combined with a computer-generated hologram (CGH); for each step the whole kinoform (FZL + CGH) is spatially shifted off-axis by a different amount of pixels to build-up the required pattern. In comparison with other SLM-based laser marking approaches already reported in the literature, our method not only eliminates (or at least significantly reduces) unwanted speckle interference but also reduces the laser power required for marking.     

Femtosecond laser writing of subwave one-dimensional quasiperiodic nanostructures on a titanium surface

One-dimensional quasiperiodic structures whose period is much smaller than the wavelength of exciting radiation have been obtained on a titanium surface under the multipulse action of linearly polarized femtosecond laser radiation with various surface energy densities. As the radiation energy density increases, the one-dimensional surface nanorelief oriented perpendicularly to the radiation polarization evolves from quasiperiodic ablation nanogrooves to regular lattices with subwave periods (100–400 nm). In contrast to the preceding works for various metals, the period of lattices for titanium decreases with increasing energy density. The formation of the indicated surface nanostructures is explained by the interference of the electric fields of incident laser radiation and a surface electromagnetic wave excited by this radiation, because the length of the surface electromagnetic wave for titanium with significant interband absorption decreases with an increase in the electron excitation of the material.     

Nanostructuring of thin gold films by femtosecond lasers

Novel experimental data on microstructuring of thin (60 nm) gold films by femtosecond laser pulses are presented and discussed. Material modifications are induced by different laser field distributions on the sample surface. Images of specially fabricated masks are transferred onto the gold surface with a 50× and 100× demagnifications. It is shown that, in the irradiated region of the gold film, the heated material tends to concentrate in the center. For example, a square-like field distribution on the target surface produces a cross with a jet in the middle. It is shown that this technique allows producing of a variety of microstructures with controllable nanorelief. Possible mechanisms leading to the observed material modifications as well as the resolution limits of this technique are discussed.     

Ultra short pulse laser annealing of FeB metallic glasses

We present the results of picosecond laser annealing of as-quenched Fe₈₅B₁₅ and Fe₈₂B₁₈ metallic glasses. The influence of the laser radiation on the surface and bulk properties are studied using CrK X-ray diffraction and transmission Mössbauer spectroscopy. The X-ray data show that the amorphous nature of the surface of the samples can be improved with laser treatment. The mat (cooling) surfaces of the ribbons appear to be more affected by the laser treatment, and show a higher stability. The Mössbauer data reveal that laser annealing of ribbon surfaces also affects the bulk properties of these materials due to induced stresses from the surface layer. The magnetic properties of these materials can be modified by laser annealing.     

Anisotropic dissolution of single-crystal silicon near the chemical mask edge on the (001) surface

The features of the micro- and nanorelief of the single-crystal silicon (001) surface formed near the vertex of the convex right corner of 〈110〉- and 〈100〉-oriented edges of a chemical mask during etching in KOH aqueous solutions (8–16 mol/l) at temperatures of 60–80°C were studied using a LEO-1420 scanning electron microscope and a MII-4 microinterferometer. It was found that microfacets formed immediately near the vertex of a convex corner of the mask are not perfect low-index microfaces of the crystal. The dependences of the crystallographic orientation and normal etch rates of such facets on experimental conditions were determined. The dependence of the effective activation energy of dissolution of the studied surfaces on the KOH concentration was estimated.     

A study of the compounds which are induced on the metallic target surface under the action of a pulsed laser plasmatron

The compounds induced on the surface of titanium and copper targets by a breakdown plasma produced by focused TEA-CO₂ high-repetition frequency laser pulses was studied by transmission electron microscopy and selected area diffraction in correlation with absorptivity data determined before and after laser irradiation. The possibility of using TEA-CO₂ lasers to produce complex thermal treatments was demonstrated for metallic surfaces by the modification of the physico-chemical properties at the sites of plasma action on these surfaces.     

X-ray analysis of mechanical and thermal effects induced by femtosecond laser treatment of aluminum single crystals

Surface marking of aluminum single crystal is performed with femtosecond laser pulses. X-ray analysis allows to measure thermal and mechanical effects induced by the femtosecond laser pulses. These effects are estimated by comparing the pole figures (crystallinity) and the broadening of the diffraction peaks (mechanical contribution) before and after the laser irradiation. The results show that the femtosecond laser treatment ensures a re-crystallization of the structure and the presence of mechanical residual stresses. The analysis of the pole figures provides the sign of a re-crystallization on smaller volumes compared to initial ones. After the laser irradiation, the crystallization is perfectly oriented like the (1 1 0) orientation of the massive sample. Moreover, following the laser treatment, we show that the crystallographic structure is purer than the initial one. We also prove that the laser effect is persistent on a typical scale of 10 μm beyond the surface.     

The effects of pulsed Nd:YAG laser irradiation on surface energy of copper

The effect of laser surface treatment on the surface energy of copper plate was investigated in terms of the surface microstructure analysis and theoretical computation in this paper. The surfaces of the copper plates were treated by Nd:YAG pulsed laser with different powers. The microstructures of the treated copper plates were analyzed by optical microscopy and X-ray diffraction (XRD), and the wetting experiment was performed to evaluate the variation of surface energy. The results showed that the surface microstructure and the corresponding surface energy of copper, changed with the variation of the laser power. The experimental results further explained by XRD results and theoretical calculation, demonstrated that the surface energy changed when the crystal structure in the surface layer was re-oriented in a preferred orientation after laser irradiation.     

F-θ镜头的光学设计

介绍一种适合于激光打标的聚焦镜头－F-θ镜头的光学设计.通过引入桶形畸变，得到的F-θ镜头的像高与入射角成正比，可实现打标速度的线性控制.优化设计得到的工作面积达500×500 mm2的F-θ镜头，结构简单紧凑、聚焦性能达到衍射极限.     

Laser cleaning of copper roofing sheets subjected to long-lasting environmental corrosion

The study was concerned with the effect of the laser fluence and pulse duration on the microstructure of copper roofing of the Wilanów Palace in Warsaw (Poland) subjected to environmental degradation since the turn 19th century. The techniques used for the microstructure examinations included: SEM+EDS, X-ray diffraction analysis, surface profiling and colour analysis. The measurements of colour of the laser-cleaned surfaces showed that series of 100-μs pulses offer the most effective cleaning. It was also found that by controlling the number of laser pulses it is possible to control the roughness of the cleaned surface.     

Observations of higher-order laser-induced surface ripples on 〈111〉 germanium

We report the observation and analysis of higher-order optical diffraction patterns arising from linear combinations of the primary laser-induced gratings or ripples on germanium surfaces. These higher-order surface structures presumably arise from nonlinear interactions between superimposed primary gratings with different grating wave vectors. For gratings produced by normally incident laser beams on Ge 〈111〉 surfaces, the diffraction patterns exhibit a strongly hexagonal symmetry.     

Van der Waals surface of InSe as a nanorelief standard in metrology of nano-objects

Rapid progress of nanotechnology requires metrological provision systems and, first of all, a standard of length in the nanometer range including a surface nanorelief standard. One such standard is the periodical arrangement of atoms in the lattice of single crystals. The cleavage surface of layered crystals is very suitable in this respect. The cleavage surface of an InSe layered semiconductor is a van der Waals surface. It features a high chemical stability and a low roughness, is easy to obtain by cleavage, and has extended atomically smooth areas of a highly ordered rhombohedral lattice with unit cell parameter a = 0.4003 nm. Therefore, this surface, like the surface of highly oriented pyrographite, can be used as a nanorelief standard.     

Influence of random,mirror surface defects on the diffraction performance of a confocal strip laser resonator

A confocal strip resonator is allowed to have random, mirror surface defects. A self-consistent field requirement involving both mirrors leads to a homogeneous integral equation with a complex-valued, nonsymmetric, random kernel. The statistics of the modulus of the first eigenvalue (which is directly related to the diffraction loss per transit) is studied via Monte Carlo type methods. It is shown that the influence of the random mirror surfaces on the diffraction performance of the laser is not small, even when the mirror surface roughness is small in magnitude.