Intensity Distribution Of Beam Research Articles

Computation of double freeform optical surfaces using a Monge–Ampère solver: Application to beam shaping

In this article, we present a formulation for the design of double freeform lens surfaces to control the intensity distribution of a laser beam with plane wavefronts. Double freefrom surfaces are utilized to shape collimated beams. Two different layouts of the freeform lens optical system are introduced, i.e., a single lens with double freeform surfaces, and two separate lenses with two flat and two freeform surfaces. The freeform lens design problem can be formulated as a Monge–Ampère type differential equation with transport boundary condition, expressing conservation of energy combined with the law of refraction and the constraint imposed on the optical path length between source and target planes. Numerical solutions are computed using a generalized least-squares algorithm which is presented by Yadav et al. (2018). The algorithm is capable to compute two solutions of the Monge–Ampère boundary value problem, corresponding to either c-convex or c-concave freeform surfaces for both layouts. The freeform surfaces are validated for several numerical examples using a ray-tracer based on Quasi-Monte Carlo simulation.

Vortex astigmatic Fourier-invariant Gaussian beams.

We find a two-parameter family of astigmatic elliptical Gaussian (AEG) optical vortices, which are free space modes up to scale and rotation. We calculate total normalized orbital angular momentum of AEG vortices, which can be an integer, fractional and zero, and which is equal to the algebraic sum of two terms reflecting the contribution of the vortex and astigmatic components of the light field. In any transverse plane, such a beam has an isolated n-fold degenerate intensity null on the optical axis (an optical vortex) embedded into an elliptical Gaussian beam. In addition to the quadratic elliptical phase, a beam has the phase of a cylindrical lens rotated by an angle of 45 degrees with respect to the principal axes of the ellipse of the Gaussian beam intensity distribution. The degenerated central intensity null in these beams does not split it into n spatially separated intensity nulls, as is usually assumed for elliptical astigmatic beams.

Инициированная ударной волной эмиссия ионов из напряженных гранитов

AbstractIn this paper, we obtained intensity distributions of beams of positively charged ions emitted from the surface of uniaxially compressed granites under the effect of a shock wave. The intensity of beams decreases exponentially with an increase in the number of shock waves. The ions fly out at the moments when the dislocations reach the surface moving in intersecting slip planes. A compressive load suppresses the dislocation release and the intensity of ion beams.

Controllable transmission of vector beams in dichroic medium**Project supported by the National Natural Science Foundation of China (Grant Nos. 11774286, 11374238, 11534008, 11604258, and 11574247), China Postdoctoral Science Foundation (Grant No. 2016M592771), and the Fundamental Research Funds for the Central Universities, China (Grant No. xjj2018213).

Vector beams with spatially varying polarization distribution in the wavefront plane have received increasing attention in recent years. The manipulation of vector beams both in intensity and polarization distributions is highly desired and under development. In this work, we study the transmission property of vector beams through warm rubidium vapor and realize controllable transmission of vector beams based on atomic dichroism. By utilizing the linearly polarized beam and vector beams as the pump and probe beams in a pump–probe configuration, a spatially-dependent dichroism can be obtained, which leads to spatially varied absorption of the probe beam. The controllable intensity distribution of the probe beam, as a two-petal pattern, can rotate with the variation of the pump beam’s polarization states. We experimentally demonstrate the mechanism of dichroism with linear polarization light and provide an explanation based on the optical pumping effect. Alternatively, the varying trend of the probe beam’s intensity is also interpreted by utilizing the Jones matrix. Our results are thus beneficial for providing potential applications in optical manipulation in atomic ensembles.

Analysis of Intensity Distribution in the He-Ne Laser Beam by Gaussian Distribution Function

The purpose of this research is to analyze the distribution of density in the laser beam, both from the experimental and theoretical point of view. I measured the density distribution through the He-Ne laser beam and prepared an attempt to compare it with the Gaussian distribution function. Image profiling can be used to determine the distance of objects depending on the distribution of the laser beam spot surroundings by their width. It can also be used to take pictures of things and define their distances and shape things. As we see, Nubia is very good. From the compatibility analysis found that (the program that made the fitting mention of GNUPLOT).

Propagation characteristics of optical vortex pulse in atmospheric turbulence

To understand the influence of atmospheric turbulence on optical vortex pulse, the transmission equation of vortex pulse beam is derived. The multiple phase-screen method is used to calculate the intensity distribution of vortex beam that influenced by atmospheric turbulence. Some main parameters, such as pulse width, the topological charge, strength of turbulence and propagation distance, are discussed in detail to show the propagation characteristics of the vortex pulse in atmospheric turbulence. Results show that with the increasing of the strength of turbulence, the vortex pulse beam is distorted more seriously. For the parameters of the vortex pulse itself, with the increasing of pulse width, the ability of resisting distortion is decreasing.

Model of a four-petal Lorentz-Gauss beam and its paraxial propagation

The concept of a four-petal Lorentz-Gauss beam was first introduced, which is consisted by Lorentz part and Gaussian part. Based on the Collins integral formula, the equation of a four-petal Lorentz-Gauss beam propagating in ABCD optical system was derived. The propagation properties of a four-petal Lorentz-Gauss bean in free space was illustrated and analyzed using numerical examples. The intensity distributions of four-petal Lorentz-Gauss beam can be modulated by the beam waist of Lorentz part, and the beam will evolve into a larger Gaussian-like beam in the center around by smaller beamlets in the far field.

In situ real-time beam monitoring with dielectric meta-holograms.

A novel approach for performing in situ and real-time beam monitoring, based on dielectric meta-hologram, is proposed and demonstrated. The ultrathin dielectric meta-hologram projects a portion of the beam power onto a screen to provide a visual indicator of the spatial intensity distribution of a Gaussian laser beam, as well as its waist position along the optical axis. Specifically, we demonstrate simple monitoring of the spot size, astigmatism, lateral position, and position along the optical axis of the beam. Good agreement is found with both theory and conventional knife-edge beam profiler measurements. This in situ beam monitoring approach could provide a highly useful tool for numerous optical applications.

Focal-space intensity distribution of an incoherent light source beam behind a focusing lens

Based on ray-tracing technique and vectorial diffraction theory, focal-space intensity distribution of an incoherent light source (ILS) beam after a focusing lens is theoretically described. We investigated the influence of different parameters (the source size, wavelength, focusing lens type, etc.) on the focal-space intensity distribution. For a point source beam, a hyperbolic lens provides 50-fold better axial intensity concentration than a spherical lens of the same focal length (10 mm). Under a chromatic hyperbolic lens, broadening of the spectral bandwidth induces an elongation of the axial intensity distribution, which however is not obvious for spherical lens focusing since the spectral broadening-induced elongation is partly overlapped with that induced by the spherical aberration. Increasing the source size will broaden the lateral intensity distribution, which first looks like a Gaussian and then evolves into a hat top. The axial and/or lateral extension of focal-space intensity would be beneficial to applications where volume heating rather than point heating is required. For example, in an ILS-excited thermal lens microscopy, extension of the intensity distribution brings a quadratic increase of photothermal signal of an ensemble sample but a linear increase of the signal for a point-like target.

Annular light bullets of a femtosecond optical vortex in a medium with anomalous group velocity dispersion

Self-action of a spatially annular femtosecond laser beam with spiral phase dislocation in a transparent dielectric with anomalous group velocity dispersion is studied. Based on numerical simulations the analysis of spatiotemporal evolution of intensity distribution in a pulsed optical vortex beam at the wavelength nm in fused silica is carried out. It is predicted the formation of annular light bullets with dynamical localization of intense laser field in thin rings with width of approximately , duration of optical oscillations and intensity higher than W cm−2.

Generation of propagation-invariant and intensity-controlled dark hollow beams by a refractive beam shaping system.

Dark hollow beams (DHBs) have great potential in the applications of optical manipulation, and the generation of DHBs is still a challenging and rewarding issue. In this paper, we present a beam shaping system for generating DHBs. The proposed system is composed of a freeform lens array and a non-classical zoom system which has a constant focal length but various image locations. The DHBs with a well-controlled intensity profile generated by the proposed system is not sensitive to the change of the intensity distribution of the incident beam, which allows flexible choices of light sources. Moreover, the annular pattern produced by the DHB remains unchanged when the image plane is moved a long distance of 17mm, and the energy efficiency of the beam shaping system is greater than 90% when Fresnel loss is considered. The proposed beam shaping system endows the generated DHBs with new properties and may have great potential in the field of optical tweezers and atom guides.

Nonparaxial propagation properties of the chirped Airy Gaussian vortex beams in uniaxial crystals orthogonal to the optical axis**Project supported by the National Natural Science Foundation of China (Grant Nos. 11775083 and 11374108)

In this article, we investigate the nonparaxial propagation properties of the chirped Airy Gaussian vortex (CAiGV) beams in uniaxial crystals orthogonal to the optical axis analytically and numerically. We discuss how the linear chirp parameters, the quadratic chirp parameters, and the Gaussian factors influence the nonparaxial propagation dynamics of the CAiGV beams. The intensity, the energy flow, the beam center, and the angular momentum of the CAiGV beams are deeply investigated. It is shown that the Gaussian factors have a great effect on the intensity and the centroid positions of the CAiGV beams. With the Gaussian factors increasing, the intensity of CAiGV beams decreases rapidly. The main lobes of the transverse intensity distribution of the CAiGV beams are similar to triangles.

Designing of Spiral-Shape Beams to Tailor Chirality of Laser-Printed Nanoneedles

Formation of a chiral nanorelief appearing on the surface of plasmonic-active metals upon their ablation with vortex and spiral-shape beam was recently found to be mainly driven by the helical-shape temperature and corresponding surface tension gradients rather than optical angular momentum transfer from the incident beam. Meanwhile, optimization of the laser intensity pattern driving the rotational movement of transiently molten metal allowing fabrication of surface structures with controlled chirality is still an actual task for various practical applications in nanophotonics and biosensing. Here, we show that by properly designing the intensity distribution in the spiral-shape beam used for direct laser ablation, the chirality of produced nanostructures can be controlled in a wide range of parameter.

Quadruple Gaussian Laser Beam Profile Dynamics in Collisionless Magnetized Plasma

This paper presents an investigation of self-focusing of a quadruple Gaussian laser beam in collisionless magnetized plasma. The nonlinearity due to ponderomotive force which arises on account of nonuniform intensity distribution of the laser beam is considered. The nonlinear partial differential equation governing the evaluation of complex envelope in the slowly varying envelope approximation is solved using a paraxial formalism. The self-focusing mechanism in magnetized plasma, in the presence of self-compression mechanism will be analyzed in contrast to the case in which it is absent. It can be observed that, in case of ponderomotive nonlinearity, the self-compression mechanism obstructs the pulse self-focusing above a certain intensity value. The effect of an external magnetic field is to generate pulses with smaller spot size and shorter compression length. The lateral separation parameter and the initial intensity of the laser beam play a crucial role on focusing and compression parameters. Also, the three-dimensional analysis of pulse propagation is presented by coupling the self-focusing equation with the self-compression one.

Controllable beam shaping of coherent and incoherent beams by a laser amplifier

We propose the technique for a controllable manipulation of the transverse intensity distribution of an output beam by the temporal adjustment of a transverse gain profile in a laser amplifier. It was created by an independent manipulation of the output powers of each of the two pump diodes. The output beam of the laser amplifier is able to vary both the output power and the transverse intensity distribution. Additionally, it was shown experimentally that this technique is valid for the case of incoherent laser beam shaping.

Customized laser beam intensity distribution for the laser surface treatment of geometrically convoluted components

The Laser Surface Hardening Process of real components must achieve a uniform hardened profile to get constant mechanical properties and must deal with the energy distribution in the proximities of geometrical singularities to prevent them from overheating. Classical approaches like the overlapped laser tracks or uniform beams by fixed optical arrangements introduce the problems of annealing and lack dynamic adaptability capability, respectively. The present work uses a galvanometric scanner to get a user-defined laser intensity distribution, by iteratively scan a flat pattern, capable of creating uniform hardened profiles and dynamically adapting in real time to handle geometrical singularities. The experimental setup to obtain it and its characteristics as a function of the scanning frequency of the flat pattern are presented. Experimental results were obtained in crankshafts of automotive engines achieving uniform hardened profiles and good surface finish around the geometrical singularities.

Application specific intensity distributions for laser materials processing: Tailoring the induced temperature profile

In laser materials processing the intensity distribution of the laser beam strongly influences the spatial and temporal temperature profile that is induced within the treated material and therefore the shape of the heat influenced zone. As a consequence, the processing quality and efficiency can be increased by using adapted intensity distributions that explicitly tailor the generated temperature profile. In this work, an efficient numerical method to calculate application specific intensity distributions is presented that induce prescribed spatial and temporal temperature profiles in the material. To this end, this task is described as an inverse heat conduction problem which is solved with the conjugate gradient method with adjoint problem. As temperature-dependent thermo-physical material properties, volumetric beam absorption and quasi-stationary distributions can be accounted for, this approach proves to be very general. The performance of the algorithm is then shown by presenting two different test cases. While the first one is taken from the application of laser softening, the second one simulates a time-dependent intensity distribution for laser transmission welding. Furthermore, ideas how to implement the obtained intensity distributions, which are very inhomogeneous, are provided using specialized beam shaping techniques. The results for both test cases are validated using commercial FEM solvers.

Influence of laser wavelength and beam profile on the coagulation depth in a soft tissue phantom model

In laser tissue soldering (LTS), a protein solution is thermally denatured and cross-linked to obtain a strong bond between tissues or tissue and a wound dressing. However, if the extension of the heat-affected zone is too large, wound healing is impaired by thermal tissue injuries. Therefore, heat input and coagulation depth have to be limited. We investigate the influence of wavelength and beam profile on coagulation depth using a soft tissue phantom in case of weakly (980 nm) and strong (1540 nm) absorbed laser radiation. The soft tissue phantom is doped with polystyrene (PS) beads to obtain similar scattering properties as natural tissue. The propagation of the laser radiation in the phantom is simulated by Monte–Carlo method and the optical penetration (OPD) depth calculated from isophotes. The simulation results are compared with the experimental determination of the coagulation volume. The results reveal that scattering effect of tissues on laser radiation increases the losses of a Gaussian beam profile laterally leading to a half-sphere coagulation volume. The depth profile of the coagulation follows approximately the intensity distribution of the laser beams as long as scattering effects are weak. As scattering effects become significant, as for 980-nm radiation, the intensity distribution of the laser beam in the tissue deviates from the original one, leading to different profile of the coagulation depth.

Development of Scribing Technique by using Multiple-laser Beams for Multi-filamentary Coated Conductors

The REBa2Cu3O7-d (REBCO) coated conductors (CCs) with the multi-filamentary structure is very useful for controlling the AC-loss and the shielding current. We have developed laser scribing technique to fabricate multi-filamentary structure by irradiating a rectangular beam using excimer laser source (KrF, λ∼248nm). Since the reflectance of stabilized silver and copper at the wavelength of Nd: YAG or fiber laser (∼ 1 μm) is 98% or more, destructive thermal processing must be required for processing in the wavelength range, which was the reason why we chose the excimer laser as light source. Actually, we successfully fabricated scribing structure with high precision. On the other hand, the improvement of the processing speed has been an important issue to be solved. Although the multi-laser beam system is effective for this purpose, the uniform intensity distribution in the width direction has to be realized. There is no strong Gaussian component in the excimer laser compared with a solid laser. The uniformity is useful for a single beam, however, it is not enough for the multi-beam system. In order to solve this issue, we have modified the beam intensity distribution by using homogenizer. Concretely, the beam intensity in the minor axis direction was flattened by a homogenizer using a plurality of horizontally elongated cylindrical lenses. This modification made the uniform range of laser intensity wider and it was confirmed that multi-laser beams can be applicable as a high-speed scribing technique.

Propagation of a vortex elliptical Airy beam

Because elliptical beams have many special properties and applications, an elliptical Airy beam with and without a vortex phase has been proposed. Based on the definition of the elliptical Airy beam, an experimental setup for the generation is given, and the formula for the evolution of the intensity is derived. Meanwhile, from the propagation of the Airy beam in vacuum, the abruptly autofocusing length is derived. Based on the formula of the abruptly autofocusing length, the intensity distributions at some special locations are analyzed and discussed, especially in the autofocusing point. Study shows that some interesting intensity profiles are reformed due to the asymmetry intensity distribution of the elliptical Airy beam and abrupt autofocusing of the circular Airy beam during propagation. The different eccentricity of the elliptical Airy beam has similar properties, such as the beam split with the propagation distance and the reformed beam shaped like a ”light knife” (very narrow beam) at some positions due to the convergence process out of synchronization along the x- and y-axis. When we impart a vortex on the elliptical Airy beam, the intensity distribution will rotate and split with the propagation distance.