Laser Beam Axis Research Articles

Ion motion in strongly magnetized cluster laser plasma

Abstract This paper investigates the interaction of high intensity, circularly polarized, short laser pulses with heavy cluster plasma through analytical modeling and numerical simulations. The optimal parameters were found for the generation of several GigaGs quasi-stationary magnetic field by using the upgraded analytical model and detailed 3D PIC simulations. It is confirmed that a field of such strength slows down the thermal expansion of the cluster core in the direction transverse to the laser beam axis, which can be used in nuclear physics. The generated inward shocks produce ion core compression, which is relevant to nuclear fusion. The electrostatic interaction between the rotating laser field, electrons and ions leads to an ion spiral density distribution in the cluster’s transversal plane, which is absent in a cluster irradiated by linearly polarized pulses with the same parameters.

Design and Analysis of 5-DOF Compact Electromagnetic Levitation Actuator for Lens Control of Laser Cutting Machine.

In laser beam processing, the angle or offset between the auxiliary gas and the laser beam axis have been proved to be two new process optimization parameters for improving cutting speed and quality. However, a traditional electromechanical actuator cannot achieve high-speed and high-precision motion control with a compact structure. This paper proposes a magnetic levitation actuator which could realize the 5-DOF motion control of a lens using six groups of differential electromagnets. At first, the nonlinear characteristic of a magnetic driving force was analyzed by establishing an analytical model and finite element calculation. Then, the dynamic model of the magnetic levitation actuator was established using the Taylor series. And the mathematical relationship between the detected distance and five-degree-of-freedom was determined. Next, the centralized control system based on PID control was designed. Finally, a driving test was carried out to verify the five-degrees-of-freedom motion of the proposed electromagnetic levitation actuator. The results show it can achieve a stable levitation and precision positioning with a desired command motion. It also proves that the proposed magnetic levitation actuator has the potential application in an off-axis laser cutting machine tool.

A new method for describing the change of the laser beam axis trajectory in the Anderson differential cuvette to measure the refractive index of liquids

A new method for describing the change of the laser beam axis trajectory in the Anderson differential cuvette to measure the refractive index of liquids

A methodology for laser tool setters calibration and its precise mathematical model

On-machine tool setting is a pivotal approach in achieving intelligent manufacturing, and laser tool setters have become a crucial component of smart machine tools. Laser tool setters play a crucial role in precisely measuring the dimensions of cutting tools during the part machining process, focusing on tool length and diameter. As a measuring instrument, the positions of the laser axis of the laser tool setter need to be accurately calibrated before use. However, in actual calibration scenarios, traditional calibration methods face challenges due to installation errors in the tool setter and geometric errors in the measuring rod. To address this issue, this study proposes a novel calibration method. Initially, the calibration mechanism of the laser beam axis is established. Based on the accurate mathematical model of the laser beam and the measuring rod, and using the polygon clipping algorithm, the mathematical mechanism of the laser tool setter's work is established. Then, a novel method is introduced to calculate the compensation distance between the laser beam reference point and the rod bottom center point at each moment during calibration. Furthermore, by utilizing the kinematic chain of the tool setter calibration system, a new calibration method is developed to accurately calibrate the position of the laser beam axis in the machine tool coordinate system. Finally, the accuracy of the calibration method is verified through simulation experiments and calibration tests. This method improves the calibration accuracy of the tool setter, and the mathematical model of the laser tool setter can be extended to the measurement of tools, thereby improving the precision of tool measurements. This research significantly improves the efficient production performance of smart machine tools.

Manipulation of femtosecond laser filamentation by wire mesh amplitude mask

The results of numerical simulation on the propagation of high-power femtosecond laser pulses in air under conditions of the amplitude modulation are presented. Laser pulse amplitude modulation is realized by using the metal mesh-masks, which divide the initial laser beam into lower-energy parts (subbeams). We show that, in general, the beam energy partitioning by metal meshes reduces the total length of beam filamentation region in air, whereas the longitudinal continuity of the laser plasma distribution in the filaments is considerably improved. A strong dependence of the filamentation region parameters (starting coordinate, length, longitudinal continuity) on the position of the mesh-mask relative to the laser beam axis is also revealed. It turns out that under certain conditions, when the beam axis points to the mesh crossing, the spatial position of the filaments can be shifted further along the propagation path by increasing the size of the mesh cells. Alternatively, if the beam center exposes the mesh cell opening, the filamentation start coordinate decreases monotonically when the mesh becomes sparser. Additionally, the parameters of the filamentation region exhibit high sensitivity to the mesh wire thickness that can dominate the influence of mesh position and cell size.

The Effect of TiN Nanoparticles on the Structure and Mechanical Properties of the Porous–Solid Steel Joint Formed by Laser-Beam Welding

The formation of a crystal structure and properties of a welded joint between a porous stainless steel plate and a solid plate of greater thickness with the use of nanomodifying additives has been experimentally investigated. To obtain a high-quality butt joint of the plates, the end layer of the solid plate was found to have been penetrated. The laser beam axis is shifted from the boundary of the plate joint by some distance, which is necessary to compensate the (material of) metal during the melting of the porous plate. The application ofnanomodifying additives reduces the grain size of the weld structure, which, in turn, has a positive effect on the mechanical properties of the resulting joint. The results of tensile strength tests have shown that the failureof nanomodified samples, unlike unmodified ones, occurred only in the main porous metal. The average value of the tensile strength is 89.5 MPa.

Spectral distribution and flux of [formula omitted]-ray beams produced through Compton scattering of unsynchronized laser and electron beams

Intense, quasi-monochromatic, polarized γ-ray beams with high and tunable energy produced by Compton scattering of laser photons against relativistic electrons are used for fundamental studies and applications. Following a series of photoneutron cross section measurements in the Giant Dipole Resonance (GDR) energy region performed at the NewSUBARU synchrotron radiation facility, we have developed the eliLaBr Monte Carlo simulation code for characterization of the scattered γ-ray photon beams. The code is implemented using Geant4 and is available on the GitHub repository (https://github.com/dan-mihai-filipescu/eliLaBr). Here we report the validation of the eliLaBr code on NewSUBARU LCS γ-ray beam flux and spectral distribution data and two applications performed with it for asymmetric transverse emittance profiles electron beams, characteristic for synchrotrons.The first application is based on a systematic investigation of transverse collimator offsets relative to the laser and electron beam axis. We show that the maximum energy of the LCS γ-ray beam is altered by vertical collimator offsets, where the edge shifts towards lower energies with the increase in the offset.Secondly, using the eliLaBr code, we investigate the effect of the laser polarization plane orientation on the properties of the LCS γ-ray beams produced with asymmetric emittance electron beams. We show that:1. The use of vertically polarized lasers contributes to the preservation of the LCS γ-ray beam maximum energy edge by increasing the precision in the vertical collimator alignment.2. Under identical conditions for the electron and laser beams phase-space distributions, the energy spectrum of the scattered LCS γ-ray beam changes with the laser beam polarization plane orientation. More precisely, the use of vertically polarized laser beams slightly deteriorates the LCS γ-ray beam energy resolution.

3D microfabrication by applying the laser-induced bubble method to the thermoset polymer PDMS using a conventional nanosecond laser.

We recently developed a microfabrication technique [microfabrication using laser-induced bubble (microFLIB)] and applied it to polydimethylsiloxane (PDMS), a thermoset polymer. The technique enabled the rapid fabrication of a microchannel on a PDMS substrate and selective metallization of the channel via subsequent plating; however, the technique was limited to surface microfabrication. Therefore, we explored the feasibility of three-dimensional (3D) microFLIB of PDMS using a nanosecond laser. In the experiment, a laser beam was focused inside pre-curing liquid PDMS and was scanned both perpendicular and parallel to the laser-beam axis to generate a 3D line of laser-induced bubbles. In the microFLIB processing, the shape of the created bubbles was retained in the pre-curing PDMS for more than 24 h; thus, the line of bubbles generated by the perpendicular laser scanning successfully produced a 3D hollow transverse microchannel inside the PDMS substrate after subsequent thermal curing. In addition, a through-hole with an aspect ratio greater than ∼200 was easily fabricated in the PDMS substrate by parallel laser scanning. The fabrication of a 3D microfluidic device comprising two open reservoirs in a PDMS substrate was also demonstrated for biochip applications.

Performance of a complementary metal-oxide-semiconductor sensor for laser guide star wavefront sensing

The adaptive optics systems of future Extremely Large Telescopes (ELTs) will be assisted with laser guide stars (LGS) which will be created in the sodium layer at a height of ≈90 km above the telescopes. In a Shack–Hartmann wavefront sensor, the long elongation of LGS spots on the sub-pupils far apart from the laser beam axis constraints the design of the wavefront sensor (WFS) which must be able to fully sample the elongated spots without undersampling the non-elongated spots. To fulfill these requirements, a newly released large complementary metal oxide semiconductor sensor with 1100 × 1600 pixels and 9 μm pixel pitch could be employed. Here, we report on the characterization of such a sensor in terms of noise and linearity, and we evaluate its performance for wavefront sensing based on the spot centroid variations. We then illustrate how this new detector can be integrated into a full LGS WFS for both the European Southern Observatory’s ELT and the Thirty Meter Telescope.

Effect of laser on double-arc physical characteristics in pulsed laser-induced double-TIG welding

In order to improve the melting efficiency of double-TIG arc, based on the synchronous induction of pulsed laser to double-arc, the coupling-enhanced discharge phenomenon between double-arcs is studied in this paper. The melting efficiency of pulsed laser-induced double-arc is quantitatively analyzed. The physical characteristics of coupling double-arc are studied based on high-speed camera and spectral diagnosis technology. The physical model is established to discuss the particle migration during the coupling discharge, characterizing the movement state of electrons. The results show that Dla (horizontal distance between the tungsten electrode tip and laser beam axis) has a significant effect on the melting efficiency of the heat source. With the increase of Dla, there are three interaction relationships between the double-arc plasma and keyhole plasma: mutual interference, coupling-enhanced discharge, and no interaction. A suitable Dla can realize the synchronous induction of laser to double-arc plasma, forming a coupling double-arc; the heat source has a higher melting efficiency. The migration of particles in double-arc can be divided into four stages: double-arc free discharge stage, laser-induced initial stage, laser-induced contraction stage, and laser-induced stable stage. Under the induction of laser, the double-arc forms a common compressed conductive channel. The energy density of coupling double-arc reaches 9.3 times that of traditional double-arc, and the total electron kinetic energy increases by 38% compared with traditional double-arc.

Effect of distance between the heat sources on energy transfer behavior in keyhole during laser-GTA welding titanium alloy

The influence of distance between heat sources (Distance between the axis of laser beam and the tip of tungsten electrode, Dla) on energy transfer behavior in keyhole during laser-arc hybrid welding titanium alloy is studied. Energy analysis method was adopted to analyze the dimension parameters and welding efficiency of welds. A “sandwich” structure consisting of SiO2 glass and titanium alloy plate was used to directly monitor the physical characteristics of hybrid arc and laser keyhole. With spectral diagnosis method, coupling discharge states of hybrid plasma under different Dla were analyzed. The experimental results show that Dla greatly affects the energy transfer mode in keyhole. Precisely adjusting Dla can change the coupling state of heat sources and the inclined angle of keyhole wall, control the energy transfer mode in keyhole, and improve the heating capacity of heat sources. In addition, two transfer modes of “bottom absorption” and “sidewall absorption” exist in keyhole. When Dla is equivalent to the length of the original arc column, the coupling state is better, the inclined angle is smaller, and the transfer mode is dominated by “bottom absorption”. When Dla is changed, the coupling state changes subsequently, the inclined angle increases and the transfer mode changes to “sidewall absorption”.

Diagnostics of peak laser intensity by pair production from thin foil target

It is known that in the small quantum parameter regime the Breit-Wheeler electron-positron pair creation cross section is extremely sensitive on the photon energy and on the background field. We present the dependence of positron yield on laser intensity in laser-foil interactions with the help of analytical theory and particle-in-cell simulaitons. These particles are emitted in a relatively narrow range of cone angles close to perpendicular direction relative to the laser beam axis. This allows for establishing an in situ intensity diagnostic by measuring the positron current in experiments where peta-watt class lasers are used.

Ultrasonic measurement of air temperature along the axis of a laser beam during interferometric measurement of length

An ultrasonic technique that allows compensation of air temperature changes and gradients along the beam axis of the laser interferometer during displacement measurement is presented.The system is based on using two ultrasonic paths parallel to the laser beam that operate at different frequencies and continuous waves emitted in opposite directions. The theoretical basis of the measurements is presented. To enable ultrasonic temperature measurement when the measuring reflector is moving, an iterative measurement algorithm is proposed. Experimental assessment of the accuracy of the method is presented. The effect of air temperature gradients along the laser beam axis is tested. The influence of air flow on the measurement accuracy is analyzed.

OPTICAL AND ELECTRONIC COMPLEX FOR CONTROL OF OPTICAL SIGHT VIEWING LINE POSITION

Method of the sights viewing line control on base of optical and electronic systems using the modern element base (laser source of irradiation and digital photo detector) is considered in paper. Essence of method is in determining of the viewing line coordinates of a sight under control relatively to laser beam or normal to mirror, which are connected unmistakably with base elements of small arms. Algebraic difference of the viewing line projection and laser beam axis or normal to mirror before and after shooting is determining a value of sight viewing line deviation after serial stage of shooting tests. There are assessed three variants of the optical and electronic complexes from view point their accuracy at control of viewing line stability at shooting tests. In the first variant, a complex includes the collimation-measuring unit and laser, which is basing unmistakably on weapon barrel and determining channel axis of it barrel. TV camera is mounting behind ocular of sight under control for increasing of accuracy of sight reticle direction to control point. In the second variant, a laser source is integrated in receiving channel structure and dismountable mirror is mounting on weapon instead of laser. Normal of that mirror is determining the axis of weapon barrel channel. In the third variant, a complex includes reflective element in view of rhombic prism. Semitransparent beam splitter is plotted on exit plane of prism. Besides that, a prism is equipped with special means for unmistakably orientation of it normal to reflective plane relatively to axis of weapon barrel channel. Prism body made from magnetic material for stable contact with edge of weapon barrel executes function of that means. Analysis of there variants accuracy has shown advantage of the third variant.

A New Optical Angle Measurement Method Based on Second Harmonic Generation with a Mode-Locked Femtosecond Laser

This paper proposes a new optical angle measurement method based on second harmonic generation with a mode-locked femtosecond laser source by taking use of the unique characteristic of high peak power and high-intensity electric field of the femtosecond laser pulses. The angle is measured from the second harmonic wave intensity, which is a function of the angle between the laser beam axis and the optic axis of a nonlinear crystal attached to the target of interest. It is found that the beta barium borate (BBO) crystal is suitable as the nonlinear crystal for this purpose through theoretical simulation. As the first step of research, an experimental demonstration is also carried out in such a way that a change of the second harmonic wave intensity due to the angular displacement of BBO crystal is measured to verify the feasibility of the proposed principle of the angle measurement method.

Research of the Treatment Parameters Effects on the Layer Formation during Wire-Feed Laser-TIG Deposition with Aluminum Alloy

The paper presents the results of an investigation of the influence parameters of laser radiation on the formation of the deposition layer during laser-TIG direct deposition of aluminum wire. Experimental studies have focused on the determination the dependence shape of layer on the laser power, the distance between axis of laser beam and axis of arc, arc parameters. High-speed video recording of the process was carried out. The metallographic analysis of cross-sections of the samples was performed.

Characteristics of quasi-unipolar electromagnetic pulses formed in the interaction of high-power laser pulses with nanoscale targets

A new method is suggested for generating quasi-unipolar electromagnetic IR and terahertz pulses. The method is based on synchronous acceleration of electrons combined to a dense bunch with a charge of up to several tens nanocoulombs, which are forced out from a nanoscale target under an action of a high-power, sharp-leading edge laser pulse. The electromagnetic bunch moving in a field of laser radiation can generate high-power electromagnetic pulses with various spectral composition including terahertz and IR ranges. A physical mechanism underlying the formation of generated quasi-unipolar pulses of electromagnetic radiation is determined and numerically studied. The pulse characteristics are found by numerical simulation, such as amplitude and duration dependences on the angle between the pulse propagation direction and laser beam axis. It is established that in modern laser installations, the amplitudes of quasi-unipolar pulses may reach relativistic values. Reflection of a unipolar pulse from an ideally reflecting surface is numerically analysed. It is shown that the pulse retains its unipolar profile in this case.

Gasdynamic effects in optical discharges produced by periodic pulse femtosecond laser

Quasi-stationary gas streams in argon (10 bar) were observed for the first time being generated by periodic-pulse optical discharge produced by laser pulses of less than 500 fs pulse length with energy up to 200 μJ/pulse and repetition rate 1.66÷10 kHz. Optical discharge was obtained in laser beam focused by off-axis (90°) parabolic mirror. In experiments the shape of the discharge zone was varied accordingly to the laser beam waist shapes varied from astigmatic to non-aberrated ones depending on the parabolic mirror tilt. Intense convective streams flowing out of the discharge volume were observed by schlieren technique. The gas streams produced could be directed normally to the laser beam axis, at some angle to the beam axis or along the beam axis toward the laser or in opposite direction. It was found that the directions of the streams produced, dynamics of their formation and their intensity were governed by the shape of the discharge zone. It was revealed that most intense and fast forming streams produced were directed normally to the laser beam axis. Two opposite streams are induced by the discharge located in astigmatic beam waist in a form of flattened “disk” ∼10 μm thick and ∼100 μm wide. The streams were directed normally to the “disk” surfaces. The energy spent on the gas flow acceleration was estimated to be up to 30% of thermal component of energy dissipated in plasma. When the focusing mirror was aligned to get no astigmatism, the gas flow generated was directed along optical axis toward the laser or backward in some cases. Refraction of the incident laser beam on the refraction index gradients of heated and excited gas injected by backward stream was followed by oscillations of the discharge zone location and generated stream direction. Discharge became stable when the gas streams were co-directional, normal or angled to the laser beam. Further studies are required to define mechanisms and possible applications of the phenomena observed.

Spatial powder flow measurement and efficiency prediction for laser direct metal deposition

Powder deposition is a critical element for coating and additive processes such as laser direct metal deposition. The flow rate and distribution of the powder affect the size of the deposited tracks and the total efficiency of the process. Therefore, knowledge of the three-dimensional shape of the powder flow and its relative position to the melt pool is crucial for any process modeling and enables an assessment of the nozzle design. Herein, a robust, industry-oriented method is proposed to measure and evaluate the 3D powder flow density from a nozzle, considering the effect of the base material. A setup was developed to measure the flow with high spatial and temporal resolution and to determine the position of the stream focus, laser beam, and tool axis. An algorithm correlates time-dependent measurement data with the spatial position of the stream, derives a volumetric distribution plot and predicts the catchment efficiency of the process considering any misalignment. The analysis of two nozzle designs reveals the influence of the powder distribution on the process capability to perform multi-layer additive manufacturing. A comparison between the predicted and actual powder catchment efficiency shows good correlation for varying standoff distances and melt pool sizes. The prediction was applied successfully by building a multi-layer structure with high geometric accuracy.

High surface quality micro machining of monocrystalline diamond by picosecond pulsed laser

In micro machining of monocrystalline diamond by pulsed laser, unique processing characteristics appeared only under a few ten picosecond pulse duration and a certain overlap rate of laser shot. Cracks mostly propagate in parallel direction to top surface of workpiece, although the laser beam axis is perpendicular to the surface. This processed area can keep diamond structure, and its surface roughness is smaller than Ra = 0.2 μm. New laser micro machining method to keep diamond structure and small surface roughness is proposed. This method can contribute to reduce the polishing process in micro machining of diamond.