Intensity Distribution Of Beam Research Articles

Correlation-induced self-focusing and self-shaping effect of a partially coherent beam

A new specially correlated partially coherent beam named nonuniform multi-Gaussian correlated (NMGC) partially coherent beam is introduced. The correlation functions of such beam in $x$ and $y$ directions are different from each other, i.e., nonuniform correlation function in one direction and multi-Gaussian correlated Schell-model function in the other direction. The propagation properties of an NMGC partially coherent beam in free pace are demonstrated, and we find that the intensity distribution of such beam exhibits self-focusing and self-shifting effect in one direction and self-shaping effect in the other direction on propagation. The correlation-induced self-focusing and self-shaping effect will be useful in some applications, where the high power and shaped laser is required, such as material thermal processing and laser carving.

Theoretical research on the generation of a submicron localized hollow beam and its applications in the trapping and cooling of a single atom

In order to generate a submicron localized hollow laser beam and realize the more efficient laser cooling and trapping of a single atom, a simple and promising scheme with using the system of a single mode fiber a circle binary phase plate and a microlens is proposed in this paper. From Rayleigh-Sommerfeld diffraction theory, the intensity distribution of the generated localized hollow laser beam near the focal plane and its propagating properties in free space are calculated. Also, the dependences of the dark-spot size of the localized hollow beam on the mode radius of single mode fiber and the focal length of the mocrolens are studied. The calculated results show that the intensity distribution of the localized hollow beam presents approximately symmstrical distribution near the focal plane. In the center of the focal plane, the light intensity is 0 and increases gradually around it. So a closed spherical light field (i.e., localized hollow laser beam) with a radius of 0.4 m is generated. The calculated results also show that the dark-spot size of the localized hollow laser beam decreases with the increasing of the microlens focal length and the decreasing of the single mode fiber mode radius. So proper parameters of this optical system can be chosen to generate localized hollow laser beams with different sizes for various applications. When the localized hollow laser beam is blue detuned, atoms will be trapped in the minimum light filed. If a repumping laser beam is applied, the trapped atoms will be also cooled by the intensity-gradient Sisyphus cooling. In this paper, we build a device for trapping and cooling a single atom by using the generated blue detuned submicron localized hollow laser beam. We study the dynamical process of intensity-gradient cooling of a single 87Rb atom trapped in the localized hollow beam by Monte-Carlo method. Our study shows that a single 87Rb atom with a temperature of 120 K (the corresponding momentum is 30ħk) from a magneto-optical trap (MOT) can be directly cooled to a final tempreture of ～ 5.8 K (the corresponding momentum is ～ 6.6ħk). So an ultracold single atom is generated and trapped in our submicro localized hollow beam. This device for obtaining ultralcold single atom can be widely uesd in the regions of the optical physics, the atom and molecule optics, such as the detecting of the fundamental physical parameters, realizing the quantum computer, studying the cold collision of singe atoms, and realizing the single atom laser.

Absorptivity Measurements and Heat Source Modeling to Simulate Laser Cladding

The laser cladding process gains importance, as it does not only allow the application of surface coatings, but also additive manufacturing of three-dimensional parts. In both cases, process simulation can contribute to process optimization. Heat source modeling is one of the main issues for an accurate model and simulation of the laser cladding process. While the laser beam intensity distribution is readily known, the other two main effects on the process’ heat input are non-trivial. Namely the measurement of the absorptivity of the applied materials as well as the powder attenuation. Therefore, calorimetry measurements were carried out. The measurement method and the measurement results for laser cladding of Stellite® 6 on structural steel S 235 and for the processing of Inconel® 625 are presented both using a CO2 laser as well as a high power diode laser (HPDL). Additionally, a heat source model is deduced.

Tangential beam intensity modulated radiotherapy versus tangential beam three-dimensional conformal radiotherapy in carcinoma breast: A dosimetric comparison and clinical correlation

Purpose: This study evaluates the dose distribution of tangential beam intensity modulated radiotherapy (IMRT) compared to tangential beam three-dimensional conformal radiotherapy (3D-CRT) in carcinoma breast. Methods: Tangential beam IMRT and tangential beam 3D-CRT plans were generated in 54 postoperative breast cancer patients. Planning target volume (PTV) definition of chest wall and intact breast was done according to Breast Cancer Atlas for Radiation Therapy Oncology Group. The prescribed dose was 50 Gy in 25 fractions. Dose volume histograms was evaluated for PTV and organs at risk, parameters of the dose distribution were compared for 3D-CRT and IMRT using Wilcoxon Matched pairs test. The dosages were clinically correlated with normal tissue reactions. Results: No difference in the conformity index but IMRT improves the homogeneity index significantly (P Conclusion: Tangential beam IMRT in breast cancer offers the potential to significantly reduce the dose-volume of the ipsilateral lung and dose volume of the heart which will translate into decrease in risk of cardiac and lung toxicity and also decreased second cancer risk. IMRT definitely decreases the acute skin reactions in all patients.

Evolution of Irradiation-Induced Vacancy Defects in Boron Nitride Nanotubes.

Irradiation-induced vacancy defects in multiwalled (MW) boron nitride nanotubes (BNNTs) are investigated via in situ high-resolution transmission electron microscope operated at 80 kV, with a homogeneous distribution of electron beam intensity. During the irradiation triangle-shaped vacancy defects are gradually generated in MW BNNTs under a mediate electron current density (30 A cm(-2)), by knocking the B atoms out. The vacancy defects grow along a well-defined direction within a wall at the early stage as a result of the curvature induced lattice strain, and then develop wall by wall. The orientation or the growth direction of the vacancy defects can be used to identify the chirality of an individual wall. With increasing electron current density, the shape of the irradiation-induced vacancy defects changes from regular triangle to irregular polygon.

Second harmonic generation by self focused q-Gaussian laser beam in preformed collisional parabolic plasma channel

Abstract This paper presents an investigation of self-focusing of a q-Gaussian laser beam and its effect on second generation in a preformed collisional parabolic plasma channel. In the presence of a q-Gaussian laser beam redistribution of carriers takes place on account of nonuniform heating produced due to collisional nonlinearity, as a result of which, a transverse density gradient is established in the channel which in turn generates plasma wave at pump frequency. Generated plasma wave interacts with the incident laser beam and generate second harmonics of the incident laser beam. Moment theory has been used to derive differential equation governing the evolution of spot size of laser beam propagating through the channel. The differential equation so obtained has been solved numerically. The effect of the intensity of laser beam, deviation of intensity distribution of laser beam along its wavefront from Gaussian distribution, plasma density and depth of channel on beam width of laser beam as well as second harmonic yield has been investigated.

Light-induced LC director freezing on a chalcogenide surface

ABSTRACTFirst observations of permanent light-induced director patterning in a transparent liquid crystal (LC) are reported. The patterning was observed in an LC cell with one of the substrates covered with a chalcogenide film. Concentric director ring pattern appears following the irradiation of the chalcogenide surface through the LC layer by a Gaussian beam. The experimental results are explained in terms of the heat transfer from the chalcogenide film to the LC after the light absorption by the chalcogenide film. Heating the LC changes its birefringence according to the spatial intensity distribution of the Gaussian beam. This in turn leads to the spatially oscillating changes of the polarisation state of light in the plane of the chalcogenide film. The oscillating changes of the light polarisation result in producing the light-induced easy orientation axis and the oscillating changes of the anchoring energy. It causes the spatial modulation of the director on the chalcogenide surface and the formation of the concentric ring twist structures in the cell.

New Ways to Generate Flat‐Top Profiles

AbstractPreviously, flat‐top beam profiles were usually generated in laser technology through homogenizers. These beam shaping optics are, however, both expensive and diminish the laser output. Optical fibers with a rectangular core geometry offer an alternative, by being able to homogenize the intensity distribution of a laser beam without reducing its performance.

Optical-soliton and chaotic motions in a nonlocal nonlinear medium

The coupled equations for the incoherent optical spatial solitons in a nonlocal nonlinear medium is studied analytically. With the soliton solutions hereby obtained via the symbolic computation, the optical-soliton motion in the nonlocal nonlinear medium is studied: is inversely related to , , and , while is positively related to and , but is independent of , with as the slowly varying amplitude of the beam, as the refractive index change, as the beam intensity distribution, as the frequency of the propagating beam, and as the unperturbed refractive index. Head-on and overtaking interactions are observed, and head-on interaction is transformed into an overtaking one with increasing. Bound-state interaction is displayed, and with increasing, the period of decreases, while that of increases. Considering the external forces in the nonlocal nonlinear medium, we explore the chaotic motions in the nonlinear nonlocal medium, including effects of the external forces on such motions. It is seen that when and , the two-dimensional attractors with stretching-and-folding structures are exhibited, and the developed chaos occurs, where and are the amplitudes of external forces, c is the speed of light in vacuum. Such chaotic motions are weakened with , , , and increasing, or with decreasing, where and represent the frequencies of external forces.

Propagation properties of partially coherent four-petal Gaussian vortex beams in turbulent atmosphere

The partially coherent four-petal Gaussian vortex beam is introduced and described by analytical expressions. The analytical propagation equation for partially coherent four-petal Gaussian vortex beam in turbulent atmosphere is derived by using the extended Huygens–Fresnel diffraction integral formula. The influences of refraction index structure, beam order n, topological charge M and the coherence length on the average intensity distributions of beam are investigated by numerical examples.

X-ray absorption, phase and dark-field tomography through a beam tracking approach.

We present a development of the beam–tracking approach that allows its implementation in computed tomography. One absorbing mask placed before the sample and a high resolution detector are used to track variations in the beam intensity distribution caused by the sample. Absorption, refraction, and dark–field are retrieved through a multi–Gaussian interpolation of the beam. Standard filtered back projection is used to reconstruct three dimensional maps of the real and imaginary part of the refractive index, and of the dark–field signal. While the method is here demonstrated using synchrotron radiation, its low coherence requirements suggest a possible implementation with laboratory sources.

Generation and propagation dynamics of Airy beam with the tunable tail

We introduce a new kind of Airy beam called Airy beam with the tunable tail, which can be generated from the elliptical flat-topped Gaussian beam. The analytical formula of Airy beam with the tunable tail is derived. Airy beam with the single tail can be obtained by adjusting the ration of the beam width of elliptical flat-topped Gaussian beam. The tail length of Airy beam can be controlled by the order N of incident beam. The normalized intensity distributions of Airy beam with the tunable tail propagating in free space are studied, and the propagation dynamics of Airy beam with the single tail are investigated. Compared with the Airy beam generated from the fundamental Gaussian beam or the flat-topped Gaussian beam, some interesting and useful information has been found.

Spatial modulation characteristics of single-photon frequency up-conversion systems pumped by Gaussian laser beam

In a Gaussian laser beam pumped single-photon frequency up-conversion system, the spatial distribution of the conversion efficiency is calculated, which strongly depends on the intensity distribution of the pump beam and leads to a spatial modulation of the output single photons. As a result, by simply varying the Gaussian pump beam intensity and the beam size, the converted photons could be modulated spatially and exhibit a programmable distribution. This will be meaningful for the researches on quantum communication and quantum manipulation based on frequency up-conversion system.

Mid-wave infrared metasurface microlensed focal plane array for optical crosstalk suppression.

Spatial crosstalk is one of the fundamental drawbacks of diminishing pixel size in mid-wave infrared focal plane arrays (IR-FPAs). We proposed an IR-FPA using the concept of optical phase discontinuities for substantial optical crosstalk suppression. This IR-FPA consists of asymmetrically tailored V-shaped optical antennas. Full-wave simulations confirmed major improvements in narrowing the intensity distribution of incident light beam by over 30-folds and concentrating these distributions in the central pixel of IR-FPA by achieving optical crosstalks of <1%.

A micro-pattern gaseous detector for beam monitoring in ion-therapy

A micro-pattern gaseous detector based on gas electron multiplier technology (GEM detector) was developed as a new transmission beam monitor for charged-particle therapy to obtain real-time information about the parameters of a therapeutic beam. Feasibility tests for the GEM detector were performed using an 80-MeV proton beam to evaluate the lateral intensity distributions of a pencil beam and the dose delivered to a target. The beam intensity distributions measured with the GEM detector were in good agreement with those measured with an imaging plate while the charge output from the GEM detector was in proportion to that of a reference dose monitor of an ionization chamber design. These experimental results showed that the GEM detector can be used not only as a beam monitor for the position and two-dimensional intensity distribution but also as a dose monitor. Thus, it is possible to simultaneously measure these beam parameters for beam control in charged-particle therapy using a single GEM-based transmission monitor.

High-quality and controllable hollow beam generation by a liquid-core optical fiber

We present the generation of high-quality and beam parameter controllable hollow beams with a liquid-core optical fiber (LCOF) filled with CS2 by adjusting off-axis orientation and LCOF structure. The dependences of the dark spot size (DSS), ring beam width (RBW) and transverse field intensity distribution of the hollow beam on the incidence angle of laser beam, the length and core diameter of the LCOF are investigated experimentally, and analyzed theoretically by using Zemax simulation. The results show that the quality of the hollow beam is related to the times of total internal reflection of skew rays in the fiber core; the DSS and RBW are closely controlled by the incidence angle and core diameter. High-quality thin-ring hollow beam is achieved experimentally by the LCOF of the core diameter of 100μm and the length of 1m with the incidence angle of less than 10°. The hollow beam generated has high stability, and is weakly dependent on the bending of the LCOF.

Impact of scribe width reduction on the back-contact insulation process for the series connection of thin-film silicon solar cells

The loss of active area due to the integrated series connection of thin-film solar cells is one of the major reasons for reduced cell-to-module efficiencies. Therefore, it is crucial to reduce the dead area losses to increase the module efficiency. In this work, the back-contact insulation process (P3) for thin-film silicon modules was evaluated for substrate side laser scribing with 532 nm. A special emphasis was placed on the influence of the P3 scribe width reduction on the electrical properties of the solar module. A strong dependence of the ablation behavior on the processing beam radius and absorber thickness was observed. Calculations of the laser beam intensity distribution predict a decrease in heat-affected zone formation when the processing beam radius decreases. However, due to an increased ablation threshold fluence, measurements showed severe deterioration of the module properties for reduced beam radii. Raman microscopy revealed good agreement between extent/degree of absorber modification at the direct scribe edge, electrical evaluation, and scribe morphology for a-Si:H solar cells, while for a-Si:H/μc-Si:H tandem cells the P3 process evaluation remains challenging.

Application of the Logarithmic Moment of an Intensity Distribution as an Alternative to the Dispersion Coefficient of a Laser Beam

We consider a quasi-Gaussian characteristic that defines the degree of deviation of the measured intensity distribution of a laser beam from a Gaussian distribution. This characteristic is an alternative to the beam dispersion coefficient M2.

Annular vortex beams with apertures and their characteristics in the turbulent atmosphere

The analytical formulas for the average intensity distribution of annular vortex beam with aperture in the turbulent atmosphere are derived based on the extended Huygens–Fresnel principle. Under the H-V 5/7 turbulence model, the propagation proprieties of annular vortex beam with aperture are studied, and the influences of the optical topological charge, the propagation distance and the laser wavelength are numerically analyzed.

Analysis of behavior of focusing error signals generated by astigmatic method when a focused spot moves beyond the radius of a land-groove-type optical disk

We theoretically calculate behaviors of focusing error signals generated by an astigmatic method in a land-groove-type optical disk. The focusing error signal from the land does not coincide with that from the groove. This behavior is enhanced when a focused spot of an optical pickup moves beyond the radius of the optical disk. A gain difference between the slope sensitivities of focusing error signals from the land and the groove is an important factor with respect to stable focusing servo control. In our calculation, the format of digital versatile disc-random access memory (DVD-RAM) is adopted as the land-groove-type optical disk model, and the dependences of the gain difference on various factors are investigated. The gain difference strongly depends on the optical intensity distribution of the laser beam in the optical pickup. The calculation method and results in this paper will be reflected in newly developed land-groove-type optical disks.