Wave Laser Research Articles

SmartPIV: flow velocity estimates by smartphones for education and field studies

In this paper, a smartphone application is presented that was developed to lower the barrier to introduce particle image velocimetry (PIV) in lab courses. The first benefit is that a PIV system using smartphones and a continuous wave (cw-) laser is much cheaper than a conventional system and thus much more affordable for universities. The second benefit is that the design of the menus follows that of modern camera apps, which are intuitively used. Thus, the system is much less complex and costly than typical systems, and our experience showed that students have much less reservations to work with the system and to try different parameters. Last but not least the app can be applied in the field. The relative uncertainty was shown to be less than 8%, which is reasonable for quick velocity estimates. An analysis of the computational time necessary for the data evaluation showed that with the current implementation the app is capable of providing smooth live display vector fields of the flow. This might further increase the use of modern measurement techniques in industry and education.Graphic abstract

Comparison of QCW pulsed laser and single-mode CW laser on the welding of power cell lugs

Aluminum alloy is the main material of pole ear plate and bus bar of power cells for new energy electric vehicles. In this paper, quasi-continuous wave (QCW) pulsed laser and single-mode continuous wave (CW) laser were used to conduct laser lap welding experiments on a 0.5 mm thick 1060 aluminum alloy and 2 mm thick 6061 aluminum alloy. The effects of these two laser sources on weld zone morphology and tensile force were compared. The experimental results show that the QCW pulsed laser welding is more likely to have porosity cracks and other defects, while the overall weld performance of the single-mode CW laser welding is obviously better than the former. In addition, the maximum tensile strength of the weld joint in QCW welding is about 861.02 N, while it can reach 1521.36 N in CW welding. The tensile force with CW laser welding is much higher than that required by the power battery industry standard, i.e., the tensile force of 800 N.

Scanning laser wave recorder with registration of “instantaneous” sea surface profiles

AbstractA direct optical method for measuring the “instantaneous” profile of the sea surface with an accuracy of 1 mm and a spatial resolution of 3 mm is described. Surface profile measurements can be carried out on spatial scales from units of millimeters to units of meters with an averaging time of 10−4 s. The method is based on the synchronization of the beginning of scanning a laser beam over the sea surface and the beginning of recording the radiation scattered on the surface onto the video camera matrix. The heights of all points of the profile are brought to a single point in time, which makes it possible to obtain “instantaneous” profiles of the sea surface with the frequency of video recording. The measurement technique and data processing algorithm are described. The errors of the method are substantiated. The results of field measurements of the parameters of sea waves are presented: amplitude spectra, distribution of slopes at various spatial averaging scales. The applied version of the wave recorder did not allow recording capillary oscillations, but with some modernization it will be possible. The method is completely remote, does not distort the properties of the surface, is not affected by wind, waves and sea currents, it allows you to measure the proportion of foam on the surface. The possibility of applying the proposed method at any time of the day and in a wide range of weather conditions has been experimentally proved.

Relapses of ingrown toenail: causes and treatment features

Introduction.The recurrent course of an ingrown toenail remains a serious problem to this day, despite the centuries-old history of its study. Among outpatient patients, the incidence of this disease reaches 10% and does not tend to decrease, and among the population, the incidence of ingrown toenail is 3.4%. Theaimof the work was to study the causes of recurrent ingrown toenail and the effectiveness of using a laser beam in the treatment of this pathology.Material and methods.The authors analyzed the causes of recurrent ingrown toenail in 66 patients after various surgical interventions for the period from 1990 to 2020.Results and discussion.The following causes of relapse of the disease were identified: removal of the entire nail plate not according to indications, carrying out marginal resection of the nail on the affected side with the preservation of the nail plate matrix, performing removal of granulations in the nail roller area with the preservation of the nail, underestimating the importance of anti-inflammatory drug treatment in the postoperative period, as well as the importance of correcting metabolic processes in patients with concomitant pathology. A clinical case is presented: a patient with a non-healing wound after four surgeries due to an ingrown toenail with a recurrent course. The patient underwent a Schmiden surgery with resection of the “ingrown edge” of the right first toe nail and removal of infected granulations using laser irradiation of the wound and careful treatment of the matrix area in the projection of the removed part of the nail. In the postoperative period, bandages with ointment based on chloramphenicol and methyluracil were used for local treatment. Recovery occurred on the fourteenth day.Conclusion.In order to reduce the number of relapses of the disease, it is recommended to perform a matrixectomy of the bed of the removed nail plate using laser or radio wave radiation.

Controlling rotation in the molecular frame with an optical centrifuge

We computationally demonstrate a new method for coherently controlling the rotation-axis direction in asymmetric top molecules with an optical centrifuge. Appropriately chosen electric-field strengths and the centrifuge's acceleration rate allow to generate a nearly arbitrary rotational wavepacket. For D$_2$S and 2H-imidazole (C$_3$H$_4$N$_2$) we created wavepackets at large values of the rotational quantum number $J$ with the desired projections of the total angular momentum onto two of the molecules' principal axes of inertia. One application of the new method is three-dimensional alignment with a molecular axis aligned along the laser's wave vector, which is important for the three-dimensional imaging of molecules yet not accessible in standard approaches. The simultaneous orientation of the angular momentum in the laboratory frame and in the molecular frame could also be used in robust control of scattering experiments.

Transportation dynamics of dielectric particles with the gradient forces in the field of orthogonal standing laser waves

We develop the theory of transportation and localization of a transparent dielectric spherical particle with the gradient forces in the interference field of orthogonally directed standing laser waves Ez(coskz) and Ex(coskx). It is shown that, when the waves Ez and Ex are coherent, the interference radiation field contains two harmonic components with the periods Λ0=π/k and ΛΔ=π/ksin(π/4). The amplitudes of the gradient force components depend on the ratio of the particle radius R to the modulation periods due to inhomogeneity of radiation in the particle volume and are given by the Bessel functions J3/2(2πR/Λ0) and J3/2(2πR/ΛΔ). We find the critical particle radii R0 and RΔ=2R0 defined by the Bessel functions zeros and corresponding to the vanishing components of the gradient forces. In particular, for the radiation with the wavelength λ0=1.064 μm and a particle in water, the smallest critical radii are R0=0.286 μm and 0.492 μm and RΔ=0.404 μm and 0.696 μm, respectively. For a number of special cases, we obtain the analytical solutions of the Newton equations and the particle trajectories that depend on the ratio of wave intensities and the particle radius. The results can be used to study the dynamics of the “optical assembly” of a two-dimensional particles matrix which behaves as a molecular crystal [Mellor and Bain, Chem. Phys. Chem. 7 (2006) 329–332].

Formation and statistical properties of rogue wave in dispersion-managed fiber lasers

Rogue wave in ultrafast fiber lasers is a hot research topic of nonlinear optics, which is generally monitored at the fixed cavity positions, despite its dramatic intra-cavity evolution. The shot-to-shot statistical properties change significantly if the chaotic pulse experiences strong changes along the cavity, which is rarely considered in the past. Here, we simulate the dynamic evolution of the rogue wave in the dispersion-managed fiber laser. Attributing to the temporal structure change induced by the dispersion, the rogue wave within the noise-like pulse appears in a limited cavity region while disappears in the rest parts. It is also demonstrated that the dispersion is capable of manipulating rogue waves in the pulse trains outside the cavity. Our results offer insightful views on the properties of chaotic waves in ultrafast lasers.

Ultrarelativistic electrons in counterpropagating laser beams

The dynamics and radiation of ultrarelativistic electrons in strong counterpropagating laser beams are investigated. Assuming that the particle energy is the dominant scale in the problem, an approximate solution of classical equations of motion is derived and the characteristic features of the motion are examined. A specific regime is found with comparable strong field quantum parameters of the beams, when the electron trajectory exhibits ultrashort spike-like features, which bears great significance to the corresponding radiation properties. An analytical expression for the spectral distribution of spontaneous radiation is derived in the framework of the Baier–Katkov semiclassical approximation based on the classical trajectory. All the analytical results are further validated by exact numerical calculations. We consider a non-resonant regime of interaction, when the laser frequencies in the electron rest frame are far from each other, avoiding stimulated emission. Special attention is devoted to settings when the description of radiation via the local constant field approximation fails and to corresponding spectral features. Periodic and non-periodic regimes are considered, when lab frequencies of the laser waves are always commensurate. The sensitivity of spectra with respect to the electron beam spread, focusing and finite duration of the laser beams is explored.

The Simulation and Experiment of In 718 in Warm Laser Shock Processing Without Coating

A modified constitutive model, combining laser shock processing and dynamic strain aging (DSA), is used to obtain the compressive residual stress field of In 718 in warm laser shock processing (WLSP) by ABAQUS VUMAT subroutine. In this work, a constitutive model with DSA is simplified by a single equation to integrate the interactions of face-centered cubic (FCC) and body-centered cubic (BCC) crystal structure. The modified Voyiadjis–Abed–Song (VAS) constitutive model is imported by a procedure code developed independently, including the Mises yield criterion application and parameter update. Based on the constitutive model and Gaussian mode laser wave, the strengthen process of WLSP in In 718 is simulated. For the experiment, 30×30×4 mm In718 specimen is strengthened by WLSP without coating. We analyze the amplitude and distribution of residual stress to explore the effect of temperature in impact regions through experiment and simulation. Predicted by the modified VAS constitutive model, the residual stress predicted by the modified VAS constitutive model agrees well with the experimental data at various temperatures. As a result, temperature softening has obvious effect on the residual stress distribution for In 718 in WLSP at 200°C. At 300°C, the residual stress amplitude has no diminution compared with 200°C due to DSA active, even there is thermal softening. DSA promotes the diffused solute atoms gathering and dislocation multiplication, that makes a flow stress reduce at a temperature range.

Multi-dimensional kinetic simulations of laser radiation absorption and electron acceleration in inhomogeneous underdense plasma

The sub-relativistic laser beam interaction with an underdense plasma is investigated via two-dimensional (2D) numerical simulations with respect to the laser polarization direction. Different parametric instabilities dominate the interaction depending on the propagation direction of the daughter waves in the simulation plane with respect to the laser field polarization and laser propagation direction. In the plane containing the laser electric field (p-polarization) the interaction is dominated by the two-plasmon decay instability and the beating of large amplitude electron plasma waves produces periodic ion density perturbations suppressing stimulated Raman scattering in the quarter critical density zone. A stronger absorption and heating of hot electrons is observed in the case where laser polarization is perpendicular to the simulation plane (s-polarization). Furthermore, by comparing a plane laser wave with a narrow beamlet, the effect of the initial transverse laser profile is proven to play an important role in exciting the filamentation instability, which competes with stimulated Brillouin scattering and affects the laser absorption and hot electron generation. A dedicated three-dimensional simulation indicates that a 2D simulation with p-polarization produces a more reliable results while the case of s-polarization overestimates the laser absorption and hot electron generation.

Application areas of the angle reflector

The article provides examples of how the device known as the «angle reflector» a few decades ago has been increasingly used in various fields of science and technology in recent years. Angle reflectors are designed to change (reflect) optical and radar rays in the direction, opposite to the original direction. At present, angle reflectors are widely used to ensure the safety of road transport on dangerous road sections. Radio wave reflectors have the same design as optical ones; therefore, in radio detection and location, angle reflectors are used to send warning signals to ship radars on bridge supports, beacons and buoys. Modern angle reflectors attached to meteorological probes allow determining the direction and speed of the wind at high altitude, which is especially important in the study of the outer space. In recent years, devices have been developed to improve the accuracy of radar stations calibration. The examples of graphical calculation of angle reflectors presented in the article clearly demonstrate the primary role of geometry in the design activity of an engineer. The graphical calculation is based on the theoretical positions of projective geometry. The design and calculation of optical systems is carried out by the graphoanalytic method, since only with a combination of graphical and analytical methods it is possible to accurately calculate the course of a light beam, laser, or radio wave and thereby determine the design parameters of the devices. The article focuses on a graphical method for calculating two types of angle reflectors using orthogonal projection, due to which modern engineers will be able to create more up-to-date designs of optical systems with a wide range of applications.

High-power transverse mode selection of Bessel–Gaussian beams

An efficient but simple scheme of an axicon-based resonator for tuning the spatial mode of high-power and high-order Bessel–Gaussian beams is proposed. This scheme is extended for two types of high-power lasers: continuous wave (CW) and Q-switched lasers. More importantly, the right axicon apex angle, the resonator optical length and the internal aperture diameter and its place inside the resonator are theoretically deduced for adjusting the transverse mode order of the laser. Furthermore, high-power Bessel–Gaussian beams with both active and passive arrangements are set up. The experimental results verify the validity of the theoretical model and the accuracy of the selected parameters. In this paper, an effective guideline is presented for designing more efficient, more compact, and easier-to-fabricate sources of high-power and high-order Bessel–Gaussian beams with transverse mode tuning.

Dynamically stable negative-energy states induced by spin-transfer torques

We investigate instabilities of the magnetic ground state in ferromagnetic metals that are induced by uniform electrical currents, and, in particular, go beyond previous analyses by including dipolar interactions. These instabilities arise from spin-transfer torques that lead to Doppler shifted spin waves. For sufficiently large electrical currents, spin-wave excitations have negative energy with respect to the uniform magnetic ground state, while remaining dynamically stable due to dissipative spin-transfer torques. Hence, the uniform magnetic ground state is energetically unstable, but is not able to dynamically reach the new ground state. We estimate this to happen for current densities $ j\gtrsim (1-D/D_c)10^{13} \mathrm{A/m^2} $ in typical thin film experiments, with $ D $ the Dzyaloshinskii-Moriya interaction constant, and $ D_c $ the Dzyaloshinskii-Moriya interaction that is required for spontaneous formation of spirals or skyrmions. These current densities can be made arbitrarily small for ultrathin film thicknesses at the order of nanometers, due to surface- and interlayer effects. From an analogue gravity perspective, the stable negative energy states are an essential ingredient to implement event horizons for magnons -- the quanta of spin waves -- giving rise to e.g. Hawking radiation and can be used to significantly amplify spin waves in a so-called black-hole laser.

Resonant effects in the spontaneous bremsstrahlung process of ultrarelativistic electrons in the fields of a nucleus and a pulsed light wave

This article focuses on the resonant high-energy spontaneous bremsstrahlung of ultrarelativistic electrons with considerable energies GeV in the field of a nucleus and a quasimonochromatic laser wave with an intensity ÷ 1017 W cm−2. Under resonant conditions within the light field the intermediate virtual electron transformed into a real particle. Therefore, the initial second order process in accordance with the fine structure constant in the laser field effectively reduced to two successive processes of the first order: the laser-stimulated Compton-effect and laser field-assisted scattering of an electron by a nucleus. In this work we derive the expressions for the resonant differential cross-sections of this processes using the simultaneous registration of the frequency and outgoing angle of the spontaneous photon and the absorption of the rth wave of photons (where r = 1,2,3,...is the resonance number). To summarize, for the first resonance of channel A, the resonant differential cross-section attains a magnitude of the ∼1012 and the third resonance of channel B attains ∼105 in units of . Finally, scientific laser pulse radiation (SLAC, FAIR, XFEL, ELI, XCELS) can be used to verify the model calculations.

Post-acceleration of electron bunches from laser-irradiated nanoclusters

In this paper the energy gain of attosecond electron bunches emitted during the interaction of intense, few-cycle linearly polarized lasers with nanoscale spherical clusters is determined. In this case electron bunches are emitted from the rear side of the cluster and are then further accelerated while co-propagating with the laser. A previous study has shown how this two-stage process readily occurs for clusters whose radii lie between the relativistic skin depth, δ r = γ 1/2 c/ω p , and the laser spot size σ L (Di Lucchio & Gibbon, Phys. Rev. STAB 18, 2015). An analytical model for focused light waves interacting with compact, overdense electron bunches in vacuum is derived heuristically from world-line equations of motion of an electron. The functional integral approach is followed under the mathematical point of view of integration with respect to a stochastic variable. The resulting picture of the laser wave crossing the electron’s trajectory leads to a finite energy gain of the electron in light–matter interaction in vacuum. The analytical theory is compared with three-dimensional PIC simulations from which trajectories of the electron bunches can be extracted. The effective increase in bunch energy is determined under realistic conditions both for the peak (mode) and the cutoff energy of the emitted bunch, in order to make quantitative comparisons with theory and the experimental findings of Cardenas et al , Nature Sci. Reports 9 (2019).

Resonant effect of the ultrarelativistic electron–positron pair production by gamma quanta in the field of a nucleus and a pulsed light wave

Resonant electron–positron pair production by a high-energy gamma quantum in the field of a nucleus and a quasi-monochromatic laser wave with the intensities – was theoretically studied. Under the resonant condition, an intermediate virtual electron (positron) in the laser field becomes a real particle. Due to this fact, the initial process of the second order in the fine structure constant of a laser field effectively reduces into the two successive processes of the first order: the laser-stimulated Breit–Wheeler process and the laser-assisted process of an intermediate electron (positron) scattering by a nucleus. It is shown that there is a threshold energy for the initial gamma quantum, which significantly depends on the number of absorbed wave photons. At the resonance, the electron–positron pair energies are determined by the outgoing angle between the momenta of the initial gamma quantum and the positron (for the channel A) or the electron (for the channel B). The differential cross-sections for the first few resonances with simultaneous registration of the energy and the outgoing angle of the positron or the electron were obtained. For the initial gamma quantum energy the resonant electron–positron pair energies for the case of the first three resonances can be measured with a very high magnitude of the differential cross-section: from ∼1013 for the first resonance to ∼108 (in the units of ) for the third resonance.

Anomalous violation of the local constant field approximation in colliding laser beams

The local constant field approximation (LCFA) is widely used in the study of QED effects in laser-matter interactions, with the justification that the classical strong-field parameter of the impinging laser beam is large. Here, the failure of this conjecture is demonstrated for an electron interacting with strong counterpropagating laser waves due to the emergence of an additional small time scale in the electron dynamics. Moreover, we identify a class of anomalous LCFA violation in which electrons turn sharply and leave the radiation formation zone much earlier than in the LCFA estimation. In contrast to previous observations of LCFA violation in a single laser beam, resulting in new low-harmonic peaks in the spectrum, here deviations from LCFA results are seen across the whole spectrum. A similar phenomenon is also demonstrated for an electron colliding with an ultrashort laser pulse. These results indicate the necessity of amending laser-plasma kinetic simulations in multiple beam laser configurations.Received 13 March 2020Revised 8 June 2020Accepted 9 February 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.013214Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHigh intensity laser-plasma interactionsQuantum electrodynamicsStrong electromagnetic field effectsAccelerators & BeamsPlasma PhysicsGeneral Physics

The Study on penetration variation of nickel ion in wastewater by laser light technology

The rapid development of industry in the world has brought serious negative effects, so pollution control and prevention is an important issue for the future environment. The discharge and treatment of metal ions in water environment are becoming more and more serious. Common heavy metal analysis methods need the support of large-scale instruments. In the study, the differently control of wavelength, temperature and concentration. Explore theoretical analysis solutions based on laser absorption and scattering, Design of metal ion analysis of laser light penetration. The influence of medium change of metal ions on the light dispersion path is measured by direct light. Preliminary results found that the 532nm wavelength laser light has a deviation in the determination of metal ions. Laser wave was analysed by water diffusion chromatography. In order to facilitate the change from large equipment to portable metal ion detection technology.

SRS of ultrashort laser pulses with nonlinear phase modulation

The SRS process in the regime of nonlinear phase modulation of laser and Stokes radiation waves is studied experimentally. The effect of the relationship between the laser and Stokes wavelengths on the value of the minimum laser pulse duration, at which an efficient SRS process is possible, is ascertained. The possibility of obtaining maximally broadband Stokes radiation pulses by matching the group velocities of the laser and Stokes pulses is demonstrated.

Fatigue properties of continuous wave and pulsed wave laser cold-wire welding of thick section AA6005-T6 aluminum alloys

The effect of laser wave modes on the fatigue behavior of laser cold-wire welding made of 4.8 mm thick AA6005-T6 aluminum alloy was investigated using continuous and pulsed wave lasers. Due to the inherent differences in these two wave laser modes, different welding parameters were used, while keeping the interaction time constant. The mechanical properties of welded joints were measured using tensile tests, while their fatigue performances were quantified using a constant amplitude force-controlled technique to obtain S-N curves. The pulsed wave laser mode produced higher fatigue resistance as compared to the continuous wave mode. The fatigue strength corresponding to the run-out condition (i.e., 107 cycles, in this study) was about 28% higher for the pulsed wave mode than for the continuous wave laser mode. At a high stress amplitude (30 MPa), the lifespan of the pulsed wave joints was about twice as high as that with continuous wave joints. These fatigue results were cross-referenced with a 3D topographic map, a 2D microhardness map, a metallographic study, and a fractographic analysis to better understand the crack nucleation and crack propagation mechanisms. A microhardness analysis performed along the cross-section of the joints did not reveal any significant difference between pulsed wave and continuous wave modes. A fractographic analysis confirmed crack propagation within the fusion zone and that 83 to 90% of cracks nucleated from the root undercuts. Topographic maps of the joints before fracture revealed that the continuous wave laser mode produces deeper and narrower (i.e., more acute) undercut defects than does the pulsed wave mode. A Weibull approach based on the biggest defects found on the fracture surfaces also confirmed that the continuous wave process produces larger defects at the root. Top defects are significantly small (55%), but they have a larger size dispersion than do root defects. Since the root undercuts act as the main stress concentrators, they are mainly responsible for the lower fatigue performance of the joints, and their sizes and shapes should be minimized during further process development of the welding process.