Single Laser Beam Research Articles

Experimental research on mechanism of collagen remodeling and excellent properties of skin incisions under dual beam laser welding

For problems of water loss caused by rapid energy dissipation and insufficient depth of heat-affected zone (HAZ) during skin welding with single laser beam. A dual beam 1064 nm semiconductor laser was used to weld incisions on the back of porcine skin, and the dual beam laser was consisted of preliminary beam and the secondary beam. The main beam is vertically incident, and the secondary beam is deflected by 30° on a vertical basis. In this study, there are three types of energy ratios of dual beam laser, which are 1:1, 2:1 and 3:1. From 77.22 J/cm2 to 135.4 J/cm2 stepped increasing energy density, the fusion performances of skin incisions after welding were comprehensively analyzed and characterized. Using Matlab and high-precision dynamometer to evaluate thermal denaturation and biomechanical properties, combined with H&E staining, Masson and Sirius red staining to analyze the microstructure characteristics, collagen deposition behavior and distribution around the HAZ of incisions after welding. The results showed that when the energy density was 102.96 J/cm2, at the energy ratio of 1:1, the collagen network structure was dense, collagen deposition was 48 %, thermal damage value was 0.39, and the immediate tensile strength was 206.3 N/cm2, which was far above the standard of wound healing performances after surgical treatment, and the thermal denaturation was controlled at a low level, realizing the reconstruction of collagen after fracture, achieving the optimal dual-beam laser welding performance, in vivo test results found that above laser type and energy ratio can reduce healing cycle into 7 days, which provided important references for later study on laser tissue welding technology.

Independent multicolored bottle-beam generation using acousto-optic spatial shaping of a femtosecond laser beam.

We report on the development of a tunable spectral and spatial frequency shaping system for ultrashort laser pulses using acousto-optic filters. The system enables the creation of arbitrary axially symmetric multi-wavelength field configurations in the Ti:sapphire laser emission range near 800 nm and controlling them at a multi-kilohertz rate. We experimentally demonstrate independent generation of two-colored annular intensity distributions from a single femtosecond laser beam and a bottle beam having the hollow cylindrical volume with the aspect ratio of 9:1. This laser beam shaping system can be useful in creating advanced setups for an optical control of cold atoms.

The velocity field behavior and the nature of deposition of microparticles in a thin layer of colloidal solution at wall heating from one and two laser beams

To date, heat transfer, convection and particle deposition have been mainly investigated for the case of homogeneous wall heating. Convection and particle deposition during local heating, when there are one or more local heating sources, have not been practically studied. Experimental studies of free convection and particle deposition in a layer of colloidal solution have been carried out. Convection was created by heating the liquid using one and two laser beams. The colloidal solution consisted of water and microscopic TiO2 particles. The novelty of the work is the demonstration of the effectiveness of local heating in creating high rates of convection and particle deposition at low energy costs. With two-point laser heating, the convection rate is higher than with single-point heating. When using two laser beams, the Marangoni number increases in comparison with single-point laser heating. As a result, the Bo number becomes lower than the critical value and the stability of the velocity field increases. In contrast to single-point heating, the use of two laser beams does not change the vortex flow pattern with increasing layer height. The particle deposition rate is higher when using a single laser beam than when using two beams and is two orders higher than the deposition without convection. An expression linking the deposition rate with time, layer height and fluid velocity is derived. The obtained results on the use of local heating sources are applicable for enhancing convection, as well as in technologies for cleaning solutions from solid impurities.

A study of error correction method based on selective focus for curved rail profile measurement

Rail profile detection is an important means of railway operation and maintenance. Currently, structured light profile measurement technology is mainly used for vehicle-mounted rail profile measurement. The body attitude of the vehicle will change as it passes by a curve, and the laser plane of the rail profile measurement device would be non-perpendicular to the rail in the local longitudinal direction, resulting in errors in rail profile measurement. To address this issue, an error correction method based on selective focus for curved rail profile measurement is proposed. The virtual 3D rail is generated with the section image of a single-beam laser and projected onto the image plane, which is then combined with the projection data of virtual 3D rail and the actual rail from the rail image to build the optimization function. The optimal auxiliary plane perpendicular to the rail’s longitudinal direction is then determined. Finally, error correction is achieved by projecting the measured data onto the optimal auxiliary plane. The effectiveness and accuracy of the proposed method are validated through experiments, demonstrating that regardless of the laser plane’s relative pitch or yaw motion with respect to the rail, the corrected profile wear measurement error was under 0.10 mm, satisfying the requirement for rail wear measurement accuracy. In this study, the plane perpendicular to the longitudinal direction of the rail was obtained through selective focus, thus providing a new insight into future work on rail profile measurement error correction.

Investigations of the scan characteristics with special focus on multi-target capability for the 2D laser scanner RIEGL miniVUX-2UAV

Abstract Due to recent improvements in sensor technology, UAV-based laser scanning is nowadays used in more and more applications like topographic surveying or forestry. The quality of the scanning result, a georeferenced 3D point cloud, mainly depends on errors coming from the trajectory estimation, the system calibration and the laser scanner itself. Due to the combined propagation of errors into the point cloud, the individual contribution is difficult to assess. Therefore, we propose an entire investigation of the scan characteristics of a 2D laser scanner without the use of the other sensors included in the system. The derived parameters include the range precision, the rangefinder offset as part of the range accuracy, the angular resolution capability and the multi-target capability of the RIEGL miniVUX-2UAV. The range precision is derived from amplitude values by a stochastic model, with observations fitting a theoretical model very well. The resolution capability in the angular direction is about twice the laser beam footprint size and therefore increases linearly for larger distances. Further, a new approach with the corresponding methodology for the investigation of multi-target capability is presented. The minimum distance between two targets to appear as separated echoes within a single laser beam is about 1.6 m and inliers within the measurement precision occur from 1.9 m separation distance. The scan attributes amplitude and deviation, which are computed during the online waveform processing, show a clear systematic relation to the range precision, also in cases of multiple echoes.

A new spin on Ashkin's laser trapping forces in the ray optics regime

We repeat the derivation of the forces of a single-beam gradient laser trap on a dielectric sphere in the ray optics regime as first reported by Ashkin; in this case, however, we investigate the impact of partial absorption of light by the sphere on these trapping forces. Our model indicates that the effect of absorption is to reduce the axial and transverse trapping forces as a function of absorption, as well as changing the axial trap position. The trap stiffness is predicted to remain relatively unchanged even for high levels of absorption. The model also predicts that a rotational force is imparted on the sphere as a consequence of absorption. The torque associated with a single ray is first derived, which is shown to increase as a function of both absorption, radius, and the angle of incidence. This enables a derivation of the torque acting on a trapped sphere as it is laterally displaced from the trapping position, which is found to increase linearly with respect to the transverse displacement of the sphere. The torque is derived to be zero for the case of no absorption, and also for the case of axial displacement of the sphere, regardless of absorption. The model reduces exactly to Ashkin's model for the case of zero absorption.

Thermal and Nonlinear Optical Properties of Sudan III.

We report the experimental and theoretical study of the diffraction patterns (DPs) and thermal properties of Sudan III. DPs are used in the calculation of the Sudan III nonlinear refractive index (NLRI), . As high as = 7.69 ×10-6 cm2/W is obtained. The study of the Sudan III thermal conductivity, TC, shows the reduction of the TC against the increase of the Sudan III temperature. The property, all-optical switching (AOS), is studied in details, both static and dynamic ones, using two, cw, visible, single mode laser beams of wavelengths 473 and 635 nm.

Alignment-Based Optically Pumped Magnetometer Using a Buffer-Gas Cell

Alignment-based optically pumped magnetometers (OPMs) are capable of measuring oscillating magnetic fields with high sensitivity in the $\mathrm{fT}/\sqrt{\mathrm{Hz}}$ range. Until now, alignment-based magnetometers have only used paraffin-coated vapour cells to extend the spin relaxation lifetimes of the alkali vapour. The drawback of these cells is that they are hand blown and are therefore time intensive, and somewhat unreliable, to produce. Buffer-gas cells, on the other hand, can be manufactured on a mass scale using microfabrication techniques. In this work we use hand-blown cells, but our methods also apply to microfabricated buffer-gas cells. We present the first demonstration of an alignment-based magnetometer using a buffer-gas vapour cell containing caesium (Cs) alkali vapour and nitrogen (${\mathrm{N}}_{2}$) buffer gas. The OPM is operated at $55{\phantom{\rule{0.1em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ and we achieve a $325\phantom{\rule{0.2em}{0ex}}\mathrm{fT}/\sqrt{\mathrm{Hz}}$ sensitivity to 10 kHz oscillating magnetic fields with an 800 Hz bandwidth. The alignment-based magnetometer uses a single low-power laser beam for optical pumping and probing and could potentially allow for more rapid commercialization of radio-frequency OPMs, due to the robustness of the one-beam geometry.

Research on new technology of laser forging coupled arc welding of E690 marine steel

PurposeThe purpose of this study is to reduce the cracks, pores and unfused defects in arc welding, improve the crystalline structure of the weld, refine its grains and improve the mechanical properties.Design/methodology/approachTaking E690 marine steel as the research object, the experiment adopts a new process method of laser forging coupled arc welding. Welding for comparative experiments. Experiments show that the “V”-shaped groove arc welding process has a larger fusion area, but has pores, the arc current is 168 A, the arc voltage is 28 V and the welding speed is 600 mm/min.FindingsIt can be seen from tensile tests that the coupling welding process has the highest tensile strength and yield strength, 872 MPa and 692 MPa, respectively, and the fracture elongation is 29.29%. The single-beam laser forging coupled arc welding process has a distance of laser and wire of 6–8 mm, a laser wavelength of 1,064 nm and the highest weld fusion ratio. The microhardness test shows that the average hardness of single-beam laser forging in the weld zone is 487.54 HV, which is 10.30% higher than that of arc welding. The average hardness in the fusion zone is 788.08 HV, which is 14.52% higher than that of the arc welding process.Originality/valueThe originality of the experiment: proposed a new process method of coupling arc repair for offshore steel forging; adopted a new process method of simultaneous coupling of single-beam short-pulse laser, double-beam short-pulse laser and arc welding; and obtained effect of pulsed laser and arc composite repair on porosity and fusion of E690 marine steel welds.

Multistage Smoothing Compressor for Multistep Pulse Compressors

Ultrahigh peak-power lasers are important scientific tools for frontier laser physics research, in which both the peak power improvement and operating safety are very important. Based on spatial-chirp-induced beam smoothing in both the near field and far field, a multistage-smoothing-based multistep pulse compressor (MS-MPC) is proposed here to further improve safety and operating convenience. In the MS-MPC, beam smoothing is not simply executed in the pre-compressor or main compressor but is separated into multiple stages. As a result, important and expensive optics are directly protected in every stage. The prism-pair-based pre-compressor induces a small spatial chirp, making it both easier to achieve than the previous multistep pulse compressor and sufficient to protect the first grating directly. Furthermore, the asymmetric four-grating compressor, which serves as the main compressor, induces a spatial chirp that further smooths the laser beam, protecting the last grating. In this way, a 10 s to 100 s petawatt laser pulse can be compressed with a single laser beam using the currently available optics. Additionally, an extra beam-smoothing stage can be added before the main amplifier to safeguard the largest amplification crystal from damage. The MS-MPC can be easily integrated into all existing PW laser facilities to improve their potential compressed pulse energy and operational safety.

A Centimeter-Scale Dielectric Metasurface for the Generation of Cold Atoms

The single-beam magneto-optical trap (MOT) based on the diffractive optical element offers a new route to develop compact cold atom sources. However, the optical efficiency in the previous single-beam MOT systems is usually low and unbalanced, which will affect the quality of the trapped atoms. To solve this issue, we developed a centimeter-scale dielectric metasurface optical chip with dynamic phase distributions, which was used to split a single incident laser beam into five separate ones with well-defined polarization states and uniform energy distributions. The measured diffraction efficiency of the metasurface is up to 47%. A single-beam MOT integrated with the metasurface optical chip was then used to trap the 87Rb atoms with numbers ∼1.4 × 108 and temperatures ∼7.0 μK. The proposed concept in this work may provide a promising solution for developing ultracompact cold atom sources.

Centroid Extraction of Laser Spots Captured by Infrared Detectors Combining Laser Footprint Images and Detector Observation Data

On-orbit geometric calibration of satellite-borne laser based on infrared detectors is the key tool to ensure the elevation measurement accuracy, and the accuracy of on-orbit geometric calibration is directly determined by laser spots captured by detectors. Mathematical methods, such as gray-scale barycenter, are widely applied for centroid extraction of spots captured by infrared detectors and completely depend on the energy values at points measured by detectors, which have low precision and are greatly affected by the consistency of the detectors and other factors at present. Based on the above question, considering the consistency between the real laser footprint shape and spot captured by detectors, a centroid extraction method of laser spots captured by infrared detectors combining laser footprint images and detector observation data is proposed for making up this defect to some extent. First, the self-adaptive “two-step method” is used to denoise footprint images hierarchically to obtain the real shape of footprints for constraining the spots captured by detectors, and then the centroids of spots are extracted by using the energy-weighted barycenter method based on regional blocks. In the experiment, Gaofen-7 (GF-7) satellite is taken as the research object, and the proposed method, as well as the other six methods, are used for the centroid extraction of laser spots captured by detectors, the calculation of calibration parameters based on the single-beam and dual-beam laser calibration models, the positioning of laser footprints, and cross verification. According to the results, the plane accuracy of centroid extraction using the proposed method is as follows: 0.34 grids for Beam 1 and 0.33 grids for Beam 2. In addition, on flat terrain, the elevation accuracy of Beam 1 and Beam 2 in 2021 is 5.2 cm and 5.0 cm, respectively, 0.6 cm and 4.2 cm higher than those in the most accurate one among other methods; the elevation accuracy in 2020 is 23.3 cm and 7.1 cm, respectively, 7.7 cm and 2.7 cm higher than those in the most accurate one among other methods. On slopes and gentle slopes, the method proposed is also superior to other methods. Since the change of pointing angle caused by satellite jitter, atmosphere, etc., between different years, the accuracy drops when laser footprints of 2020 are located using the parameters of 2021. In summary, under different terrains and years, the results fully demonstrate the effectiveness and accuracy of the proposed method, which has more significant advantages than other traditional methods.

Synthesis, band gap structure and third order non-linear optical properties of zinc tungsten oxide nanocomposite using a single CW laser beam.

In this study, a composite of zinc tungsten oxide nanoparticles (W-ZnO NPs) has been synthesized via mixing Na2WO4 and zinc acetate in water, followed by dropwise addition of NaOH. The synthesized W-ZnO NPs were characterized using measurement methods such as XRD, dynamic light scattering (DLS), Scanning electron microscopy (SEM) and UV-Vis. Also, the results were compared with the pure synthesized ZnO and WO3 NPs. Non-linear optical properties of the synthesized composite were measured using the Z-scan technique with a continuous wave Nd-Yag laser. The negative non-linear absorption coefficient of the components was obtained which indicates that the saturation absorption occurred in this composite. In comparison with pure ZnO NPs, non-linear absorption decreases which can be attributed to the negligible optical response of WO3 structures. Also, the negative value of the close aperture Z-scan curve shows that the thermal lensing effect is the main reason for the third-order non-linear refraction.

Bibliometric analysis of holographic data storage literature

Objectives. Snapshots of data can be stored in a holographic medium at varying depths. Data can be written via a spiral data channel in spinning holographic media in the form of circular disks like CDs or DVDs. This data is then read by shining a reference beam through the refraction following writing. However, holographic storage is distinct from CD/DVD media in the sense that information is encoded in all three dimensions. Two-dimensional data is written using a single laser beam that spirals around the material. Prototype holographic storage solutions use minuscule cones formed by individual snapshots or pages to store one million pixels. As compared with magnetic disks and tapes, which have a finite lifespan of 50 years at most, the longevity and dependability of optical media storage is advantageous for long-term archiving. Holographic technology allows for the portability of data-intensive media such as broadcast or high-definition video. However, the shelf life of holographic media remains low due to its sensitivity to light. The primary goals of most storage devices are more storage space and faster data transport. Holographic storage devices have the potential to outperform traditional optical storage devices both in terms of capacity and performance. The present paper aims to evaluate the current international research trends in Holographic Data Storage (HDS) and produce a graphical mapping of co-authorship and countries.Methods. The major outputs of the dataset were authors, document type, publication, institution, nation, and citations. After exporting 1052 data sources, HistCite software was used to analyze the citations; visualization mapping was carried out using VOSviewer software and R programming language for the analysis of the authorcountry-title association on Holographic Storage Devices.Results. The most prominent authors, papers, journals, organizations, and nations in the field of HDS were identified in HistCite. Then, four clusters were investigated using VOSviewer based on author keywords, citation collaboration networks among different organizations, countries, and the HDS co-authorship network.Conclusions. During the study period from 2000–2020 (21 years), 4636 authors contributed to 1052 publications. The highest number of publications was in 2009, with a linear adjustment of R2 = 0.0136. The most prolific author, Lee J., published 3.14% of the articles on this subject. In terms of country distribution, Japan took first-place ranking, claiming 16.54% of the total number of articles. The “holographic” keyword was used in 62.55% of the articles.

Self-focusing effect of focused array beams propagating from the space orbit through the atmosphere to the ground

For the incoherent beam combination, the self-focusing effect of focused array beams propagating from the space orbit through the atmosphere to the ground is studied. It is shown that the self-focusing effect in the atmosphere becomes stronger as the fill factor increases. When the circumcircle diameter and the fill factor of array beams are fixed, the self-focusing effect in the atmosphere becomes stronger as the element number N decreases. However, for the maximal beam compression case, the self-focusing effect in the atmosphere can assist delivering much more powerful array beams from the space orbit to the ground as N increases, and an array beam has the advantage to deliver powerful laser beam compared with a single laser beam. In particular, an effective design rule for maximal compression without filamentation of transported array beams from orbit to the ground is derived.

An Integrated Single-Beam Three-Axis High-Sensitivity Magnetometer

Three-axis atomic magnetometers have great advantages for interpreting information conveyed by magnetic fields. Here, we demonstrate a compact construction of a three-axis vector atomic magnetometer. The magnetometer is operated with a single laser beam and with a specially designed triangular 87Rb vapor cell (side length is 5 mm). The ability of three-axis measurement is realized by reflecting the light beam in the cell chamber under high pressure, so that the atoms before and after reflection are polarized along two different directions. It achieves a sensitivity of 40 fT/Hz in x-axis, 20 fT/Hz in y-axis, and 30 fT/Hz in z-axis under spin-exchange relaxation-free regime. The crosstalk effect between different axes is proven to be little in this configuration. The sensor configuration here is expected to form further values, especially for vector biomagnetism measurement, clinical diagnosis, and field source reconstruction.

Electronic‐Resonance‐Enhanced Coherent Raman Spectroscopy with a Single Femtosecond Laser Beam

AbstractCoherent Raman scattering (CRS) spectroscopy holds versatile applications in many fields ranging from measuring temperature and concentration in reacting flows to imaging biological molecules in living cells. Although the powerful spectroscopic technique has been studied for a few decades, significant attention is still paid to developing state‐of‐the‐art CRS spectroscopy with the simpler design and higher sensitivity for practical applications in harsh or complex environments. Herein, a novel electronic‐resonance‐enhanced coherent Raman scattering (ERE‐CRS) technique is developed with a single femtosecond laser beam. Such single‐beam ERE‐CRS scheme is accomplished with the narrowband air lasing signal naturally generated in the interaction region as a probe source. The developed technique not only avoids fine spatio‐temporal control in the conventional multibeam configuration, but also accomplishes 1–2 orders of magnitude enhancement of Raman signal due to the resonance of air lasing with electronic transition of the target gas. The dramatic enhancement effect is also manifested through the comparative measurements in CO2 isotopes. The single‐beam ERE‐CRS spectroscopy shows an unprecedented opportunity for the high‐sensitivity standoff detections of gas‐phase molecules and plasmas.

New insight into microstructure and mechanical properties of heterostructures 7075 Al joint prepared via single mode laser welding

The application of lightweight and high-strength Al alloys are crucial to reduce energy consumption and emissions in today's world. The lightweight and high strength 7 series aluminum alloy is widely used in aerospace, but its poor welding performance has been a bottleneck restricting the further lightweight of structural parts. In this work, a lightweight and high-strength Al joint with a tensile strength of ∼400 MPa was successfully prepared by single mode laser beam welding using non-weldable 7075 aluminum alloy as the experimental mode. The superfine laser beam reduces the volume of molten pool and increases the solidification rate of molten pool, which significantly inhibits the growth behavior of each microstructure, thus refining the microstructure. The geometrically necessary dislocations (GND) density of each microstructure of 7075 joint after tensile test was: 1.32 × 1014 m−1 for EZ, 1.21 × 1014 m−1 for CLZ, HAZ is 1.17 × 1014 m−1 for HAZ. The synergistic effect of heterogeneous microstructure and work hardening enhanced the tensile strength of 7075 joint. Furthermore, TEM, FIB and EBSD were used to characterize the fracture behavior of the 7075 joint in detail. TEM images showed that the discordant interface between α-Al grain boundary and SiO2 particle was the potential source of crack initiation. The microstructure refinement design and technical selection strategy of the work provide a new insight for laser welding of lightweight and high strength 2xxx/7xxx aluminum alloy.

Recent Advances on High‐Speed and Holographic Two‐Photon Direct Laser Writing

AbstractTwo‐Photon Lithography, thanks to its very high sub‐diffraction resolution, has become the lithographic technique par excellence in applications requiring small feature sizes and complex 3D pattering. Despite this, the fabrication times required for extended structures remain much longer than those of other competing techniques (UV mask lithography, nanoimprinting, etc.). Its low throughput prevents its wide adoption in industrial applications. To increase it, over the years different solutions have been proposed, although their usage is difficult to generalize and may be limited depending on the specific application. A promising strategy to further increase the throughput of Two‐Photon Lithography, opening a concrete window for its adoption in industry, lies in its combination with holography approaches: in this way it is possible to generate dozens of foci from a single laser beam, thus parallelizing the fabrication of periodic structures, or to engineer the intensity distribution on the writing plane in a complex way, obtaining 3D microstructures with a single exposure. Here, the fundamental concepts behind high‐speed Two‐Photon Lithography and its combination with holography are discussed, and the literary production of recent years that exploits such techniques is reviewed, and contextualized according to the topic covered.

Wavelength selection for spectrally combined laser beams propagating in free space and the atmosphere

Wavelength selection has a major impact on spectral beam combining (SBC) of laser beams that propagate in free space and in the atmosphere. We derive analytical expressions for the intensity and four characteristic quality parameters of free-space SBC beams. We show that the peak intensity, the mean-square beam width, and the M 2 factor of an SBC beam at the target are all larger than those of one single laser beam of the same power and average wavelength. The peak intensity can be made higher by increasing the wavelength spacing but reducing the mean wavelength. However, when an SBC laser beam propagates in the atmosphere, the beam quality depends on the absorption coefficient of the multi-wavelength field due to thermal blooming. A thermal distortion number is introduced for an SBC beam and its validity is confirmed. We show that the power proportion of a high-absorption element within an SBC beam should be as low as possible to reduce the thermal blooming effect.