Laser Beam Configuration Research Articles

Three-dimensional, multi-wavelength beam formation with integrated metasurface optics for Sr laser cooling.

We demonstrate the formation of a complex, multi-wavelength, three-dimensional laser beam configuration with integrated metasurface (MS) optics. Our experiments support the development of a compact Sr optical-lattice clock, which leverages magneto-optical trapping at 461 nm and 689 nm without bulk free-space optics. We integrate six mm-scale metasurfaces on a fused silica substrate and illuminate them with light from optical fibers. The metasurfaces provide full control of beam pointing, divergence, and polarization to create the laser configuration for a magneto-optical trap. We report the efficiency and integration of the visible laser beam configuration, demonstrating the suitability of metasurface optics for atomic laser cooling.

Enhancement of skin tumor laser hyperthermia with Ytterbium nanoparticles: numerical simulation

Laser hyperthermia therapy (HT) has emerged as a well-established method for treating cancer, yet it poses unique challenges in comprehending heat transfer dynamics within both healthy and cancerous tissues due to their intricate nature. This study investigates laser HT therapy as a promising avenue for addressing skin cancer. Employing two distinct near-infrared (NIR) laser beams at 980 nm, we analyze temperature variations within tumors, employing Pennes’ bioheat transfer equation as our fundamental investigative framework. Furthermore, our study delves into the influence of Ytterbium nanoparticles (YbNPs) on predicting temperature distributions in healthy and cancerous skin tissues. Our findings reveal that the application of YbNPs using a Gaussian beam shape results in a notable maximum temperature increase of 5 °C within the tumor compared to nanoparticle-free heating. Similarly, utilizing a flat top beam alongside YbNPs induces a temperature rise of 3 °C. While this research provides valuable insights into utilizing YbNPs with a Gaussian laser beam configuration for skin cancer treatment, a more thorough understanding could be attained through additional details on experimental parameters such as setup, exposure duration, and specific implications for skin cancer therapy.

Dynamical modeling of bi-layer Aluminium adhesive tape for laser shock applications

The presented work covers the response of Aluminium tape (Al tape) under high strain rate of deformation (order of 106s−1) using laser shock. High power laser (J) with a short pulse duration (ns) is used to create laser shock within the water confinement regime on two Al tape configurations in order to apply low and high pressure (order of MPa and GPa). Al tape has been modeled using Johnson-Cook (J-C) material model for the Al layer, and Steinberg–Cochran–Guinan (SCG) material model (elastic with pressure dependence) for the adhesive layer, both material models are coupled with Grüneisen equation of state. The Al tape model has been validated by comparing the simulated Back Face Velocity (BFV) of the target with the measured one by the Velocity Interferometer System for Any Reflector (VISAR). In addition, the validated material model is used to conduct the sensitivity studies about the transmitted pressure depending on the acoustical impedance of the target and adhesive thickness. Moreover, location and magnitude of maximum tensile stress within the target are calculated in function of the adhesive thickness of the Al tape. Finally, it has been proved that using one laser beam configuration, maximum tensile zone could appears close to the front face by increasing the adhesive thickness.

Vacuum breakdown in magnetic dipole wave by 10-PW class lasers.

The vacuum breakdown by 10-PW-class lasers is studied in the optimal configuration of laser beams in the form of an m-dipole wave, which maximizes the magnetic field. Using 3D PIC simulations we calculated the threshold of vacuum breakdown, which is about 10PW. We examined in detail the dynamics of particles and identified particle trajectories which contribute the most to vacuum breakdown in such highly inhomogeneous fields. We analyzed the dynamics of the electron-positron plasma distribution on the avalanche stage. It is shown that the forming plasma structures represent concentric toroidal layers and the interplay between particle ensembles from different spatial regions favors vacuum breakdown. Based on the angular distribution of charged particles and gamma photons a way to experimentally identify the process of vacuum breakdown is proposed.

Enhancing TEM00-Mode Solar Laser With Beam Merging and Ring-Array Concentrator

Abstract It is reported here a large improvement in numerically calculated TEM00-mode side-pumped solar laser efficiency, and brightness figure-of-merit by pumping two thin Nd:YAG laser rods simultaneously with a ring-array solar energy primary concentrator. Two side-pumping configurations were investigated. A single-rod configuration was used to pump a typical single thick laser rod with the full collection area of the ring-array concentrator, and a dual-rod to pump two thin laser rods simultaneously. A three-folding-mirror laser beam merging technique was used, enabling the emission of only one laser beam from the two rods. For the dual-rod single laser beam configuration, 27.50 W continuous-wave TEM00-mode solar laser output power was numerically achieved, corresponding to 16.10 W/m2 TEM00-mode solar laser collection efficiency, 1.70% solar-to-laser power conversion efficiency, 25.00 W brightness figure-of-merit, and 1.54% brightness conversion efficiency, being 1.46, 1.30, 1.75, and 1.40 times, respectively, higher than the previous numerical records, and also 2.04, 1.60, 3.87, and 2.03 times, respectively, more than the previous state-of-the-art experimental records.

Particle trajectories, gamma-ray emission, and anomalous radiative trapping effects in magnetic dipole wave.

In studies of interaction of matter with laser fields of extreme intensity there are two limiting cases of a multibeam setup maximizing either the electric field or the magnetic field. In this work attention is paid to the optimal configuration of laser beams in the form of an m-dipole wave, which maximizes the magnetic field. We consider in such highly inhomogeneous fields the advantages and specific features of laser-matter interaction, which stem from individual particle trajectories that are strongly affected by gamma photon emission. It is shown that in this field mode qualitatively different scenarios of particle dynamics take place in comparison with the mode that maximizes the electric field. A detailed map of possible regimes of particle motion (ponderomotive trapping, normal radiative trapping, radial, and axial anomalous radiative trapping), as well as angular and energy distributions of particles and gamma photons, is obtained in a wide range of laser powers up to 300 PW, and it reveals signatures of radiation losses experimentally detectable even with subpetawatt lasers.

Detection, Acquisition and Processing of Fluorescence from Cold Atoms in Cesium Fountain Primary Frequency Standard at NPL, India

In this paper, detailed geometry of the detection chamber, configuration of detection probe laser beams, data acquisition and processing techniques of the cold atoms in Cs atomic fountain primary standard at NPL, India has been discussed. The S/N ratio in the detected atom count was too low to make a valid estimate of signal. By implementing an efficient design of detection hardware (especially changing photodiode with lower junction capacitance) and software, the S/N ratio in NPLI-CsF1 has been improved significantly (~ 10 times). Details of the detection hardware and software used for better processing of the signal are given in this paper. This paper also depicts the precise computer control for data processing and the improvements in signal to noise ratio in the context of fountain operation.

Evidence for laser-induced homogeneous oriented ice nucleation revealed via pulsed x-ray diffraction.

The induction of homogeneous and oriented ice nucleation has to date not been achieved. Here, we report induced nucleation of ice from millimeter sized supercooled water drops illuminated by ns-optical laser pulses well below the ionization threshold making use of particular laser beam configurations and polarizations. Employing a 100 ps synchrotron x-ray pulse 100 ns after each laser pulse, an unambiguous correlation was observed between the directions and the symmetry of the laser fields and that of the H-bonding arrays of the induced ice crystals. Moreover, an analysis of the x-ray diffraction data indicates that, in the main, the induced nucleation of ice is homogeneous at temperatures well above the observed and predicted values for supercooled water.

Powder incorporation and spatter formation in high deposition rate blown powder directed energy deposition

A high deposition rate blown powder directed energy deposition process is presented. Clad tracks are deposited and the process is observed by high-speed imaging. An island of unmelted powder forms inside the melt pool, in the centre of the laser spot, which can be attributed to the highly focussed powder flow and the laser beam configuration used. On contact with the melt pool, the powder grains melt to join the melt pool, or they overcome surface tension and are engulfed by the melt. Powder grains can also incorporate into a mushy zone that may be present on the powder island. The powder island appears to rotate in the melt pool and incorporates relatively slowly. The speed of rotation is connected to the size of the island, which also depends on the energy density used. Spatter can form from the edges of the melt pool or from areas around the island when molten metal droplets burst. Frames from high-speed videos are presented and reasons for the various phenomena observed are discussed.

In vitro CO2 9.3-μm short-pulsed laser caries prevention-effects of a newly developed laser irradiation pattern.

Caries prevention with different lasers has been investigated in laboratory studies and clinical pilot trials. Objective of this in vitro study was to assess whether 9.3-μm microsecond short-pulsed CO2 laser irradiation enhances enamel caries resistance without melting, with and without additional fluoride application. Seven groups of enamel, totaling 105 human enamel samples, were irradiated with 2 different carbon dioxide lasers with 2 different energy application systems (original versus spread beam; 9.3μm wavelength, pulse repetition rate 43Hz vs 100Hz, fluence ranges from 1.4 to 3.9J/cm2, pulse duration 3μs to 18μs). The laboratory pH-cycling was performed with or without additional fluoride, followed by cross-sectional microhardness testing. To assess caries inhibition, the mean relative mineral loss delta Z (∆Z) was determined. To evaluate for melting, scanning electron microscopy (SEM) examinations were performed. For the non-laser control groups with additional fluoride use, the relative mineral loss (ΔZ, vol% × μm) ranged between 512 ± 292 and 809 ± 297 (mean ± SD). ΔZ for the laser-irradiated samples with fluoride use ranged between 186 ± 214 and 374 ± 191, averaging a 58% ± 6% mineral loss reduction (ANOVA, P < 0.01 to P < 0.0001). For the non-laser-treated controls without additional fluoride, the mineral loss increased (ΔZ 914 ± 422 to 1224 ± 736). In contrast, the ΔZ for the laser-treated groups without additional fluoride ranged between 463 ± 190 and 594 ± 272 (P < 0.01 to P < 0.001) indicative of 50% ± 2% average reduction in mineral loss. Enhanced caries resistance was achieved by all applied fluences. Using the spread beam resulted in enhanced resistance without enamel melting as seen by SEM. CO2 9.3-μm short-pulsed laser irradiation with both laser beam configurations resulted in highly significant reduction in enamel mineral loss. Modifying the beam to a more homogenous profile will allow enamel caries resistance even without apparent enamel melting.

Optimal laser beam configurations for laser cutting of metal sheets

The most recent developments in high power laser sources and handling optical systems create new options for optimizing the cutting process. However the selection of an optimal configuration is not evident since in laser cutting of metal sheets, the interaction between the laser and the material is geometrically complex. From an energetic point of view, parameters such as wavelength, polarization and beam shape can be optimized for different materials and thicknesses and, in theory, can significantly increase process efficiency. This paper offers an overview of possible techniques for such optimization and discusses their practical implications.

Effect of laser beam configuration on microstructure evolution and joint performance in laser joining AA 6111 panels

Control of solidification through the selection of laser beams is an approach to improve the quality of visible coach-peel joints in automotive bodies. Laser joining of aluminum alloy 6111 panels with the addition of AA 4047 filler wire was investigated in this study using three types of laser beam, single-beam, in-line beam, and cross-beam. To compare the effect of laser beam arrangement on the weld qualities, the transient heat flow, cooling rate, and solidification rate were analyzed by three-dimensional finite element thermal models using ANSYS software. Microstructure evolution, surface roughness, and fracture mechanism of joints were investigated accordingly. Using the same processing parameters for the three joining processes, cross-beam laser generated the highest peak temperature and solidification rate, as well as the smallest molten pool size. Fusion-brazing joining achieved by the cross-beam laser resulted in the best weld surface quality with acceptable mechanical properties for application as non-load-bearing components. Therefore, cross-beam laser is recommended to join aluminum closure panels in the automotive body-in-white fabrication.

Laser irradiation uniformity for polar direct drive on ShenGuang III facility

Inertial confinement fusion utilizes sufficient laser beams to directly illuminate a spherical capsule, or convert the laser into thermal X-rays inside a high Z hohlraum to drive capsule implosion. The direct drive implosion is one of ways toward central ignition and similar to the indirect drive implosion, but has higher laser energy coupling efficiency and the potential for higher-gain implosion than indirect drive, and needs stringent laser condition. In order to develop and execute the direct drive experiment on the laser facility, which is configured initially for indirect drive, the polar direct drive has been proposed and validated on the Omega laser facility and the National Ignition Facility. The polar direct drive repoints some of the beams toward the polar and equator of the target, thus increasing the drive energy on the polar and equator of capsule and achieving the most uniform irradiation. The present article focuses on the laser irradiation uniformity of the target in polar direct drive on ShenGuangIII (SGIII) facility. Firstly, the laser beam configuration of the SGIII, the characteristics of laser spots, the laser beam repointing strategy and the principle of optimization are introduced. The 48 laser beams are distributed over four cones per hemisphere and the beam centerlines are repointed in polar direct drive. The continuous phase plates (CPPs) of the SGIII are designed to have unique shape to make the laser beam with a 250 m-radius circular section at the laser entrance hole in indirect drive, and thus the laser beams have ellipse cross sections with fixed major axis and different minor axes in different cones. Then, the irradiation uniformity of 540 m target is optimized by the three-dimensional (3D) view factor method on the assumption that the laser intensity distribution is super-Gaussian with three and five orders, and the energy deposition distributions are expressed as cos2 and cos . The irradiation nonuniformity of less than 5% on the polar direct drive capsule of 540 m in diameter is achieved. The pressure distribution of the hot spot at the neutron bang time with the optimized parameter is also simulated by Multi2D, and the results of 2D hydrodynamics simulation indicate that the hot spot under the assumption of cos distribution is more symmetric. Finally, the effects on irradiation uniformity of the beam-to-beam power imbalance, the repointing error and the target pointing error are estimated by the Monte Carlo method. According to the simulation results, the laser root mean square nonuniformity on the target will not become worse observably when the maximal beam-to-beam power imbalance is limited to a value of 5%, and the repointing error and the target pointing error are better than 7 m.

Effect of the laser intensity profile on the shock non-uniformity in a directly driven spherical target

An axially symmetric laser beam configuration irradiating a spherical capsule has been considered in the context of inertial confinement fusion (ICF). The laser beams are located at co-latitudes 49° and 131° and mimic the quad positions in the second cone of the Laser Mégajoule Facility. The capsule is directly irradiated by the laser beams whose energy deposition generates a nearly spherical shock wave. Two-dimensional hydrodynamic numerical simulations have been performed to analyse the non-uniformity of the shock wavefront launched inward throughout the target. Different laser intensity profiles, calculated by the illumination model, have been tested. The performance, in terms of shock non-uniformity, has been compared, and it is found that with an appropriate choice of the laser intensity profile it is possible to control the shock non-uniformity at early times.

Enhancement of optical emission signal in double-pulse laser ablation of titanium in vacuum

Laser plasma of Ti produced in vacuum was studied by optical emission spectroscopy. The plasma was produced in a single-pulse and a double-pulse mode of ablation in a collinear configuration of laser beams. It was shown that there is a significant enhancement in emission intensity in double-pulse mode. Moreover, depending on the delay time between laser pulses in double-pulse mode signal enhancement (up to 18-fold) was further optimized. Measurement of emission from neutral and ionized Ti atoms showed that there is an optimal delay time for which emission enhancement is maximal, for both ions and neutrals. It was shown that using double-pulse laser ablation the enhancement is mostly pronounced when emission from plasma near the target surface is taken into account. This increases the limit of detection and the signal/background ratio.

Overlapping laser profiles used to mitigate the negative effects of beam uncertainties in direct-drive LMJ configurations

A direct-drive shock ignition scheme in the context of the Laser MegaJoule facility has been considered. The irradiation uniformity provided by two laser beam configurations using a total of 10 or 20 quads to drive the first compression phase has been analyzed. Firstly, a numerical method is used to optimize the laser intensity profiles in the context of the illumination approximation model; then these profiles are used to calculate the irradiation non-uniformity of a spherical target of radius r 0 = 1000 μm assuming the beam uncertainties: power imbalance 5%, pointing error 50 μm and target positioning 20 μm. These uncertainties deteriorate the quality of the irradiation increasing considerably the irradiation non-uniformity; moreover, it is found that the pointing error provides the major contribution to the degradation of the irradiation. A strategy to mitigate the negative effect induced by the beam uncertainties is proposed. It consists in using a composite profile in each beam: a first large and flat intensity profile provides a background that reduces pointing error and target positioning effects, whilst a second overlapping profile optimizes the illumination irradiation. It is found that the introduction of the flat background with an intensity of 55% with respect to the maximum intensity reduces by about 40% the non-uniformity of the irradiation due to beam uncertainties.

Property and Quality Optimization of Laser Welded Rheo-Cast F357 Aluminum Alloy

F357, a hypo-eutectic Al-7%Si-0.6%Mg alloy without beryllium, was processed with CSIR-Rheo technology to the Semi-Solid Metal (SSM) state and cast in plates by means of High Pressure Die Casting. The castings were either left in the as-cast (F) condition or subjected to T4 or T6 heat treatments prior to autogenous Nd:YAG laser welding. A welding operating window was established and within this window, the weld porosity and undercut were minimised. Butt welds complying with ISO 13919-2: 2001 could be produced by means of the optimum parameters of 3.8 kW laser power and a welding speed of 4 m/min with a twin spot laser beam configuration. The mechanical properties of age-hardenable Al-Si-Mg alloys are dependent on the rate at which the alloy is cooled after the solution heat treatment. The low heat input provided by the laser welding process resulted in high enough cooling rates to ensure that both the fusion zone and HAZ were in the T4 condition after welding. Tensile properties equivalent to the parent metal in T6 condition were obtained after subjecting welded T4 plates to conventional artificial ageing treatment.

Mechanism of near-field Raman enhancement in two-dimensional systems

A theory describing the near-field Raman enhancement in two-dimensional (2D) systems is presented. The analysis quantifies the near-field Raman intensity as a function of the tip-sample distance, Raman polarizability tensor components, incident laser beam configuration, and tip orientation relative to the sample plane. Our results show that the near-field Raman intensity is inversely proportional to the 10th and 8th power of the tip-sample distance in the incoherent and coherent scattering regimes, respectively. Optimal conditions for the tip inclination angle for different configurations are determined, and the results can be used as a guide for tip-enhanced Raman spectroscopy (TERS) experiments in 2D systems such as graphene, two-dimensional electron gases, and topological insulators.

Synthetic magnetic fluxes on the honeycomb lattice

We devise experimental schemes able to mimic uniform and staggered magnetic fluxes acting on ultracold two-electron atoms, such as ytterbium atoms, propagating in a honeycomb lattice. The atoms are first trapped into two independent state-selective triangular lattices and are further exposed to a suitable configuration of resonant Raman laser beams. These beams induce hops between the two triangular lattices and make atoms move in a honeycomb lattice. Atoms traveling around each unit cell of this honeycomb lattice pick up a nonzero phase. In the uniform case, the artificial magnetic flux sustained by each cell can reach about two flux quanta, thereby realizing a cold atom analogue of the Harper model with its notorious Hofstadter's butterfly structure. Different condensed-matter phenomena such as the relativistic integer and fractional quantum Hall effects, as observed in graphene samples, could be targeted with this scheme.

Discretely tunable optofluidic compound microlenses

We report a novel method to fabricate high zoom-ratio optofluidic compound microlenses using poly(dimethylsiloxane) with multi-layer architecture. The layered structure of deformable lenses, biconvex and plano-concave, are self-aligned as a group. The refractive index contrast of each lens, which is controlled by filling the chambers with a specific medium, is the key factor for determining the device's numerical aperture. The chip has multiple independent pneumatic valves that can be digitally switched on and off, pushing the liquid into the lens chambers with great accuracy and consistency. This quickly and precisely tunes the focal length of the microlens device from centimetres to sub-millimetre. The system has great potential for applications in portable microscopic imaging, bio-sensing, and laser beam configuration.