Nonlinear propagation of an intense Laguerre-Gaussian laser pulse in a plasma channel

The nonlinear propagation of an intense Laguerre-Gaussian(LG)laser pulse in a parabolic preformed plasma channel is analyzed by means of the variational method.The evolution equation of the spot size is derived including the effects of relativistic self-focusing,preformed channel focusing,and ponderomotive self-channeling.The parametric conditions of the LG laser pulse and plasma channel for propagating with constant spot size,periodically focusing and defocusing oscillation,catastrophic focusing,and solitary waves are obtained.Compared with the laser pulse with fundamental Gaussian(FG)mode,it is found that the effect of vacuum diffraction is reduced by half and the effects of relativistic and wakefield focusing are decreased by a quarter due to the hollow transverse intensity profile of the LG laser pulse,while the effect of channel focusing is the same order of magnitude with that of the FG laser pulse.Thus,the matched condition for the intense LG laser pulse with constant spot size is released obviously,while the parameters of the laser and plasma for the existence of solitary waves nearly coincide with those of the FG laser pulse.

Direct acceleration of electrons using two crossed Laguerre-Gaussian laser beams in vacuum

The basic physical characteristics of electrons accelerated by two linearly polarized and circularly symmetric crossed Laguerre-Gaussian （LG） laser beams with equal frequency and amplitude in vacuum are studied in detail. The condition, under which electrons can be accelerated effectively, and the energy gain are discussed.

Two-Dimensional Laguerre-Gaussian Asymmetric Soliton Family in Strongly Nonlocal Media

我们在强烈非局部的非线性的媒介表明高顺序的 Laguerre-Gaussian 不对称的空间光 solitons 的一个宽广的班的存在。而且，我们讨论特定的价值(q = 0 ) 为拓扑的费用的不同合理价值的调整深度参数详细。我们的结果显示出那高顺序的不对称现象空间 soliton 家庭能在各种各样的表格存在，例如二维的缺点 half-solitons，不对称的单个层、多层的项链 solitons。

Acceleration and radiation of externally injected electrons in laser plasma wakefield driven by a Laguerre-Gaussian pulse

By using three-dimensional particle-in-cell simulations, externally injected electron beam acceleration and radiation in donut-like wake fields driven by a Laguerre-Gaussian pulse are investigated. Studies show that in the acceleration process the total charge and azimuthal momenta of electrons can be stably maintained at a distance of a few hundreds of micrometers. Electrons experience low-frequency spiral rotation and high-frequency betatron oscillation, which leads to a synchrotron-like radiation. The radiation spectrum is mainly determined by the betatron motion of electrons. The far field distribution of radiation intensity shows axial symmetry due to the uniform transverse injection and spiral rotation of electrons. Our studies suggest a new way to simultaneously generate hollow electron beam and radiation source from a compact laser plasma accelerator.

相反拓扑指数的Laguerre-Gaussian模的产生和模间相互作用的实验研究

实验研究了带有相反拓扑指数的Laguerre-Gaussian(LG)模间的相互作用,发现含有相反拓扑指数的两个LG模在传播过程中其光场发生变化,观察到随着传播距离的增加,两个LG模的中心位相奇点会逐渐连成为一个弧形暗线形状.实验上验证了带有相反拓扑指数的光学涡流中的螺旋位错在传播过程中会演变为边位错这一理论结果.

Generation of Laguerre-Gaussian beam from end-pumped and c-cut Nd:YVO_4 laser

We demonstrate an end-pumped, c-cut Nd：YVO4 laser that emitted first-order Laguerre-Gaussian （LGol） beam by adjusting the position of focused pump beam relative to laser crystal. The pumping light reached the laser crystal has circular and solid intensity profile. The laser is compact and stable, and the obtained LG01 beam power reaches 202 mW with -25% slope efficiency.

Electron pulse train accelerated by a linearly polarized Laguerre-Gaussian laser beam

A linearly polarized Laguerre–Gaussian(LP-LG)laser beam with a twist index l=−1 has field structure that fundamentally differs from the field structure of a conventional linearly polarized Gaussian beam.Close to the axis of the LP-LG beam,the longitudinal electric and magnetic fields dominate over the transverse components.This structure offers an attractive opportunity to accelerate electrons in vacuum.It is shown,using three-dimensional particle-in-cell simulations,that this scenario can be realized by reflecting an LP-LG laser off a plasma with a sharp density gradient.The simulations indicate that a 600 TW LP-LG laser beam effectively injects electrons into the beam during the reflection.The electrons that are injected close to the laser axis experience a prolonged longitudinal acceleration by the longitudinal laser electric field.The electrons form distinct monoenergetic bunches with a small divergence angle.The energy in the most energetic bunch is 0.29 GeV.The bunch charge is 6 pC and its duration is approximately 270 as.The divergence angle is just 0.57°(10 mrad).By using a linearly polarized rather than a circularly polarized Laguerre–Gaussian beam,our scheme makes it easier to demonstrate the electron acceleration experimentally at a high-power laser facility.

Additive Manufacturing of Metal Micro-ring and Tube by Laser-Assisted Electrophoretic Deposition with Laguerre-Gaussian Beam

We report a method for laser-assisted electrophoretic deposition using a Laguerre-Gaussian beam for maskless patterning of metal rings and tubes.These are structures of utmost importance,particularly in photonic devices.Metal nanoparticles,which are gathered in a colloidal solution by a laser trapping technique,are deposited on a substrate via electrophoresis.The deposition pattern is dependent on the focused spot shape during laser trapping.The intensity distribution of the Laguerre-Gaussian beam is ring-shaped.Rings with different inner diameters can be fabricated by varying the topological charge of the Laguerre-Gaussian beam.The equivalent inner diameters of the deposited rings with topological charges of 1,3,and 5 were 0.30,0.78,and 1.45μm,respectively.The inner diameter of the deposited ring with a topological charge of 1 was smaller than the wavelength of the laser beam(532 nm).A tube was also fabricated with a topological charge of 3 by vertical displacement of the deposition cell.The deposition technology developed here using Laguerre-Gaussian beam will contribute to advancements in the fabrication of photonic and nano-fluidic devices.

Average Capacity of OAM-Multiplexed FSO System with Vortex Beam Propagating Through Non-Kolmogorov Turbulence

The propagation of vortex beam in atmospheric turbulence is of significant importance in theoretical study and practical applications. Based on extended Huygens-Fresnel integral and the Rytov approximation, the average capacity of orbital angular momentum(OAM)-multiplexed Laguerre-Gaussian(LG) beam propagating through non-Kolmogorov turbulence is presented, and the analytical expression of spiral spectrum of LG beam has been deduced. The average capacity of FSO system is numerically calculated and the influence of exponent parameter, transmission height, structure constant, wavelength, outer scale and inner scale on average capacity are also analyzed in detail. Outcomes show that smaller structure constant, outer scale, higher transmission height and larger wavelength, inner scale are conducive to improve average capacity in different extent. Results acquires in this paper have potential application value in optical communication within non-Kolmogorov turbulence.

Composite optical vortices in noncollinear Laguerre–Gaussian beams and their propagation in free space

Taking two Laguerre-Gaussian beams with topological charge 1 = ±1 as an example, this paper studies the composite optical vortices formed by two noncollinear Laguerre-Gaussian beams with different phases, amplitudes, waist widths, off-axis distances, and their propagation in free space. It is shown by detailed numerical illustrative examples that the number and location of composite vortices at the waist plane are variable by varying the relative phase β, amplitude ratio η, waist width ratio ξ, or off-axis distance ratio μ. The net topological charge lnet is not always equal to the sum lsum of charges of the two component beams. The motion, creation and annihilation of composite vortices take place in the free-space propagation, and the net charge during the propagation remains unchanged and equals to the net charge at the waist plane.

Study on holographic grating diffraction for Laguerre–Gaussian beam generation

Laguerre-Gaussian beams, as a special model with spiral phase structure, have been intensively investigated. Holographic grating method is a convenient method of generating Laguerre-Gaussian beams and measuring their orbital angular momenta. But due to some inevitable adverse factors such as lateral displacement, angular deflection and elliptical incident profile of incident beam, the practical effectiveness should be reevaluated. This paper is devoted to the study on the influences of the abovementioned three adverse factors on the holographic grating method. The characteristics of the mode decomposition of diffractive order and the relative powers of the orbital angular momentum eigen-states are also given.

Approximate analytical expressions of apertured broadband beams in the far field

The approximate analytical expressions of the apertured broadband beams in the far field with Gaussian and Laguerre-Gaussian spatial modes are presented. For the radially polarized Laguerre-Gaussian beam, the result reveals that the electromagnetic field in the far field is transverse magnetic. The influences of bandwidth （Г） and truncation parameter （Co） on the transverse intensity distribution of the Gaussian beam and on the energy flux distribution of radially polarized Laguerre-Gaussian beam are analysed.

HG-LG Mode Conversion with Stressed 3-Mode Fibers under Polarization

We have coupled an upright HG mode into a fiber-optic waveguide and used the application of stress to generate a Laguerre-Gaussian laser mode. We have generalized previous results by McGloin et al. by using a polarized input beam, a true 3-mode fiber and by applying the stress on a stripped piece of the optical waveguide. These generalizations are necessary in order to perform quantum information experiments and obtain reliable information on the stress imposed on the optical fiber.

用叉形光栅实现光子轨道角动量的叠加态的测量

Laguerre Gaussian(LG)模是光子的轨道角动量的本征态 .提出了用一种特殊的光栅———“分数阶叉形光栅”来实现两种LG模的叠加 ,它在以光子角动量为编码空间的高维量子通信领域存在潜在的应用 .

Measuring orbital angular momentum of vortex beams in optomechanics

Measuring the orbital angular momentum(OAM)of vortex beams,including the magnitude and the sign,has great application prospects due to its theoretically unbounded and orthogonal modes.Here,the sign-distinguishable OAM measurement in optomechanics is proposed,which is achieved by monitoring the shift of the transmission spectrum of the probe field in a double Laguerre-Gaussian(LG)rotational-cavity system.Compared with the traditional single LG rotational cavity,an asymmetric optomechanically induced transparency window can occur in our system.Meanwhile,the position of the resonance valley has a strong correlation with the magnitude and sign of OAM.This originally comes from the fact that the effective detuning of the cavity mode from the driving field can vary with the magnitude and sign of OAM,which causes the spectral shift to be directional for different signs of OAM.Our scheme solves the shortcoming of the inability to distinguish the sign of OAM in optomechanics,and works well for high-order vortex beams with topological charge value±45,which is a significant improvement for measuring OAM based on the cavity optomechanical system.

Laser transverse modes of spherical resonators:a review [Invited]

The study of structured laser beams has been one of the most active fields of research for decades, particularly in exploring laser beams with orbital angular momentum. The direct generation of structured beams from laser resonators is deeply associated with the formation of transverse modes. The wave representations of transverse modes of spherical cavities are usually categorized into Hermite–Gaussian(HG) and Laguerre–Gaussian(LG)modes for a long time. Enormous experimental results have revealed that the generalized representation for the transverse modes is the Hermite–LG(HLG) modes. We make a detailed overview for the theoretical description of the HLG modes from the representation of the spectral unitary group of order 2 in the Jordan–Schwinger map.Furthermore, we overview how to derive the integral formula for the elliptical modes based on the Gaussian wave-packet state and the inverse Fourier transform. The relationship between the HLG modes and elliptical modes is linked by the quantum Fourier transform. The most striking result is that the HLG modes can be exactly derived as the superposition of the elliptical modes without involving Hermite and Laguerre polynomials.Finally, we discuss the application of the HLG modes in characterizing the propagation evolution of the vortex structures of HG beams transformed by an astigmatic mode converter. This overview certainly provides not only a novel formula for transverse modes, but also a pedagogical insight into quantum physics.

LG11-mode vortex Nd:YAG laser by applying second-order circular Dammann grating for annular pumping

The excitation of liigh-order Laguerre-Gaussian (LG) modes in a neodymiuni-doped yttrium aluminum gamet (Nd:YAG) laser resonator was presented by applying the diffraction of a second-order circular Dammann grating (CDG) for annular pumping. In the study, the 808 nm pump light was shaped into a double-ring structure by the CDG and matched spatially with that of an ideal LGn mode. As a result, the laser resonator generated an LGn vortex mode, and the laser power reached 204 mW with 14.5% slope efficiency. Also, when the cavity mirror was tilted, the laser output could switch to the LG01vortex mode. The results showed the convenience and versatility of CDG in an annular-pumped vortex laser.

Geometric transformations of optical orbital angular momentum spatial modes

orbital angular momentum;;entangled state representation;;Laguerre-Gaussian

OAM effects in relativistic laser plasma interactions

When a relativistic laser pulse of high photon density interacts with a specially tailored thin foil target,a strong torque is exerted on the resulting spiral-shaped foil plasma,or"light fan".Because of its structure,the latter can gain significant orbital angular momentum(OAM),and the opposite OAM is imparted to the reflected light,creating a twisted relativistic light pulse.Using such a relativistic LaguerreGaussian(LG)laser interaction with a solid foil,we can get intense high order vortex harmonics.Besides that,proton acceleration using LG laser and hollow screw-like drill in plasma using LG laser are studied.All interaction scenarios are demonstrated by particle-in-cell simulation as well as analytical modeling,and should be verifiable in the laboratory.As important characteristics,twisted relativistic light pulse has strong torque and ultra-high OAM density,which may lead to many more new effects.