The generation and reconnection of magneticflux ropes in a plasma irradiated by two Laguerre–Gaussian laser pulses with different frequen-cies and opposite topological charges are investigated numerically by particle-...The generation and reconnection of magneticflux ropes in a plasma irradiated by two Laguerre–Gaussian laser pulses with different frequen-cies and opposite topological charges are investigated numerically by particle-in-cell simulations.It is shown that twisted plasma currents and hence magneticflux ropes can be effectively generated as long as the laser frequency difference matches the electron plasma frequency.More importantly,subsequent reconnection of magneticflux ropes can occur.Typical signatures of magnetic reconnection,such as magnetic island formation and plasma heating,are identified in the reconnection of magneticflux ropes.Notably,it is found that a strong axial magneticfield can be generated on the axis,owing to the azimuthal current induced during the reconnection of the ropes.This indicates that in the reconnection of magneticflux ropes,the energy can be transferred not only from the magneticfield to the plasma but also from the plasma current back to the magneticfield.This work opens a new avenue to the study of magneticflux ropes,which helps in understanding magnetic topology changes,and resultant magnetic energy dissipation,plasma heating,and particle acceleration found in solarflares,and magnetic confinement fusion devices.展开更多
We study the strong nonlinear optical dynamics of nanosecond pulsed Laguerre–Gaussian laser beams of high-order radial modes with zero orbital angular momentum propagating in the fullerene C60molecular medium. It is ...We study the strong nonlinear optical dynamics of nanosecond pulsed Laguerre–Gaussian laser beams of high-order radial modes with zero orbital angular momentum propagating in the fullerene C60molecular medium. It is found that the spatiotemporal profile of the incident pulsed Laguerre–Gaussian laser beam is strongly reshaped during its propagation in the C60molecular medium. The centrosymmetric temporal profile of the incident pulse gradually evolves into a noncentrosymmetric meniscus shape, and the on-axis pulse duration is clearly depressed. Furthermore, the field intensity is distinctly attenuated due to the field-intensity-dependent reverse saturable absorption, and clear optical power limiting behavior is observed for different orders of the input pulsed Laguerre–Gaussian laser beams before the takeover of the saturation effect;the lower the order of the Laguerre–Gaussian beam, the lower the energy transmittance.展开更多
We theoretically analyze the transient properties of a probe field absorption and dispersion in a coupled semiconductor double-quantum-dot nanostructure.We show that in the presence of the Gaussian laser beams,absorpt...We theoretically analyze the transient properties of a probe field absorption and dispersion in a coupled semiconductor double-quantum-dot nanostructure.We show that in the presence of the Gaussian laser beams,absorption and dispersion of the probe field can be dramatically influenced by the relative phase between applied fields and intensity of the Gaussian laser beams.Transient and steady-state behaviors of the probe field absorption and dispersion are discussed to estimate the required switching time.The estimated range is between 5-8 ps for subluminal to superluminal light propagation.展开更多
This paper presents an investigation on the self-focusing/defocusing of chirped Gaussian laser beam in collisional plasma with linear absorption. We have derived the differential equation for the beam width parameter ...This paper presents an investigation on the self-focusing/defocusing of chirped Gaussian laser beam in collisional plasma with linear absorption. We have derived the differential equation for the beam width parameter by using WKB and paraxial approximations and solved it numerically. The effect of chirp and other laser plasma parameters is seen on the behavior of beam width parameter with dimensionless distance of propagation. The results are discussed and presented graphically. Our simulation results show that the amplitude of oscillations decreases with the distance of propagation. Due to collisional frequency, the laser beam shows fast divergence which can be minimized by the introduction of chirp parameter. The chirp decreases the effect of defocusing and increases the ability of self-focusing of laser beam in collisional plasma.展开更多
Laser-driven ion accelerators have the advantages of compact size,high density,and short bunch duration over conventional accelerators.Nevertheless,it is still challenging to generate ion beams with quasi-monoenergeti...Laser-driven ion accelerators have the advantages of compact size,high density,and short bunch duration over conventional accelerators.Nevertheless,it is still challenging to generate ion beams with quasi-monoenergetic peak and low divergence in experiments with the current ultrahigh intensity laser and thin target technologies.Here we propose a scheme that a Laguerre–Gaussian laser irradiates a near-critical-density(NCD)plasma to generate a quasi-monoenergetic and low-divergence proton beam.The Laguerre–Gaussian laser pulse in an NCD plasma excites a moving longitudinal electrostatic field with a large amplitude,and it maintains the inward bowl-shape for dozens of laser durations.This special distribution of the longitudinal electrostatic field can simultaneously accelerate and converge the protons.Our particle-in-cell(PIC)simulation shows that the efficient proton acceleration can be realized with the Laguerre–Gaussian laser intensity ranging from 3.9×10^(21)W·cm^(-2)–1.6×10^(22)W·cm^(-2)available in the near future,e.g.,a quasi-monoenergetic proton beam with peak energy~115 MeV and divergence angles less than 5°can be generated by a 5.3×10^(21)W·cm^(-2)pulse.This work could provide a reference for the high-quality ion beam generation with PWclass laser systems available recently.展开更多
The generation of terahertz(THz)waves via the beating of two high-intensity chirped Gaussian lasers in a multi-ion-species plasma is numerically studied by taking into account the weak relativistic and ponderomotive r...The generation of terahertz(THz)waves via the beating of two high-intensity chirped Gaussian lasers in a multi-ion-species plasma is numerically studied by taking into account the weak relativistic and ponderomotive regime of interaction.The coupled differential equations for beamwidth parameters are extracted by introducing the dielectric function of such plasma and using WKB and paraxial ray approximations.The amplitude of THz radiation at beat frequency resulting from the nonlinear current density induced by the beat ponderomotive force of the cross-focusing of beams was obtained.The impacts of the chirp frequency parameter,initial laser intensity and initial ionic species density(specifically,the presence of singly and doubly charged ions)in the plasma on THz generation were discussed.Our numerical results reveal that THz radiation generation strongly depends on the chirp frequency parameter.A specific range of chirp frequencies exists for self-focusing as well as THz generation with a'turning point',where the THz emission reaches its maximum value.The results show that the strength of self-focusing and consequently the generated THz radiation are reduced by increasing the density of doubly charged ionic species in the plasma due to the suppression of the nonlinear effects.展开更多
This work reveals an exploration of self-focusing of Hermite-cosine-Gaussian laser beam in a collisionless plasma under relativistic nonlinearity. Self-focusing along with self-trapping of Hermite-cosine-Gaussian lase...This work reveals an exploration of self-focusing of Hermite-cosine-Gaussian laser beam in a collisionless plasma under relativistic nonlinearity. Self-focusing along with self-trapping of Hermite-cosine-Gaussian laser beam are analyzed for different values of laser intensity, plasma density, and decentered parameters. Mathematical analysis displays that these parameters play a major role in achieving the stronger and earlier self-focusing. Further, a comparative study between self-focusing of Hermite-cosine-Gaussian laser beam with and without exponential density ramp profile is introduced. Plasma density transition with exponential profile is found to be more effective in order to have stronger self-focusing. The present analysis may lead to very useful applications in the field of efficient harmonic generation, laser driven fusion etc.展开更多
The present paper is aimed to study the effect of Gaussian laser light on first and second sound waves in superfluid helium theoretically using optoacoustic method. The mechanism applied in this study is electrostrict...The present paper is aimed to study the effect of Gaussian laser light on first and second sound waves in superfluid helium theoretically using optoacoustic method. The mechanism applied in this study is electrostriction mechanism. This study considers crystal parts of superfluid helium with a zero absorption coefficient applying electrostriction mechanism. Affecting Gaussian laser light on these crystal parts, a spectrum of cylindrical first and second sound waves and cylindrical slow and rapid waves is obtained. Meanwhile, frequency of waves amplitudes proportionate to time period of laser light is calculated.展开更多
We present in this paper an investigation of the nonlinear process of above-threshold ionization. The process arises when an atomic or molecular system, exposed to an intense laser pulse, continues to absorb more phot...We present in this paper an investigation of the nonlinear process of above-threshold ionization. The process arises when an atomic or molecular system, exposed to an intense laser pulse, continues to absorb more photons than that needed for the ionization to occur. We trigger this nonlinear process in a simple molecular system by exposing it to an intense transform-limited Gaussian laser pulse of 267-nm wavelength which is the third harmonic of an 800-nm wavelength Tisapphire laser. We explore the characteristics of the process by analyzing the kinetic-energy spectra of the electrons ejected from the molecular system under different laser peak intensities.展开更多
A new near-infrared direct acceleration mechanism driven by Laguerre-Gaussian laser is proposed to stably accelerate and concentrate electron slice both in longitudinal and transversal directions in vacuum.Three-dimen...A new near-infrared direct acceleration mechanism driven by Laguerre-Gaussian laser is proposed to stably accelerate and concentrate electron slice both in longitudinal and transversal directions in vacuum.Three-dimensional simulations show that a 2-μm circularly polarized LG_(p)^(l)(p=0,l=1,σ_(2)=-1)laser can directly manipulate attosecond electron slices in additional dimensions(angular directions)and give them annular structures and angular momentums.These annular vortex attosecond electron slices are expected to have some novel applications such as in the collimation of antiprotons in conventional linear accelerators,edge-enhancement electron imaging,structured X-ray generation,and analysis and manipulation of nanomaterials.展开更多
In this paper, according to the temperature and strain distribution obtained by considering the Gaussian pump profile and dependence of physical properties on temperature, we derive an analytical model for refractive ...In this paper, according to the temperature and strain distribution obtained by considering the Gaussian pump profile and dependence of physical properties on temperature, we derive an analytical model for refractive index variations of the diode side-pumped Nd：YAG laser rod. Then we evaluate this model by numerical solution and our maximum relative errors are 5% and 10% for variations caused by thermo–optical and thermo–mechanical effects; respectively. Finally, we present an analytical model for calculating the focal length of the thermal lens and spherical aberration. This model is evaluated by experimental results.展开更多
Laser transformation hardening(LTH) is one of the laser surface modification processes.The surface hardening of rod-shaped carbon steel(SM45C) was performed by lathe-based laser composite processor with Gaussian-beam ...Laser transformation hardening(LTH) is one of the laser surface modification processes.The surface hardening of rod-shaped carbon steel(SM45C) was performed by lathe-based laser composite processor with Gaussian-beam optical head.The LTH characteristics by dominant processes,longitudinal and depth directional hardness distributions and behaviors of phase transformation in hardened zones were examined.Especially,two concepts of circumferential speed and theoretical overlap rate were applied.When laser power increased or circumferential speed decreased,the surface hardening depth gradually increases due to the increased heat input.Moreover,the longitudinal hardness distribution particularly shows periodicity of repetitive increase and decrease,which results from tempering effect by overlap.Finally,the feasibility of laser transformation hardening is verified by using the beam with Gaussian intensity distribution.展开更多
A single-mode laser system with non-Gaussian and Gaussian noise is investigated. The stationary mean value and the normalized variance of the laser intensity are numerically calculated under the condition that the sta...A single-mode laser system with non-Gaussian and Gaussian noise is investigated. The stationary mean value and the normalized variance of the laser intensity are numerically calculated under the condition that the stationary probability distribution function （SPDF） is derived. The SPDF as a function of the laser intensity exhibits a maximum, The maximum becomes smaller with the increase of the correlation intensity or the non-Gaussian parameter, where the later is a measure of the deviation from the Gaussian characteristic. The maximum becomes larger as the correlation time increases. The laser intensity stationary mean value decreases with the increase of the correlation intensity or the non-Gaussian parameter while increases with the correlation time increasing. The laser intensity normalized variance increases with the increase of the correlation intensity or the non-Gaussian parameter while decreases as the correlation time increases.展开更多
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 i...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.展开更多
Using time-dependent multilevel approach （TDML）, this paper studies the dynamics of coherent control of Rydberg lithium atoms and demonstrates that Rydberg lithium atoms can be transferred to states of higher princi...Using time-dependent multilevel approach （TDML）, this paper studies the dynamics of coherent control of Rydberg lithium atoms and demonstrates that Rydberg lithium atoms can be transferred to states of higher principal quantum number by exposing them to specially designed frequency-chirped laser pulses. The population transfer from n=70 to n=75 states of lithium atoms with efficiency more than 90% is achieved by means of the sequential adiabatic rapid passages. The results agree well with the experimental ones and show that the coherent control of the population transfer from the lower n to the higher n states can be accomplished by the optimization of the chirping parameters and the intensity of laser field.展开更多
激光无线传能(Laser Wireless Power Transmission,LWPT)系统中,传能激光光束质量直接影响传能效率,为了提高传能光束质量,提出了一种基于反高斯算法的激光光场匀化策略:首先建立激光光束的高斯数学模型,进而求出该高斯函数的反函数,得...激光无线传能(Laser Wireless Power Transmission,LWPT)系统中,传能激光光束质量直接影响传能效率,为了提高传能光束质量,提出了一种基于反高斯算法的激光光场匀化策略:首先建立激光光束的高斯数学模型,进而求出该高斯函数的反函数,得到对应的反高斯函数,再将该高斯函数与反高斯函数相乘,则得到一个常数。由此表明,高斯激光光束通过反高斯处理后,可以实现匀化;基于该策略,设计了反高斯光场匀化方案置,以此构建了基于反高斯匀化的激光无线传能系统模型。仿真实验结果表明,反高斯匀化策略与现有的激光光束整形方法相比,在不依赖复杂光学元件组与加工精度要求的前提下,光束发散角为6 mrad,光强均匀度达到了83%。由此可见,匀化效果明显,为激光无线传能系统效率提升提供了新的解决方案。展开更多
We propose a new laser-plasma-based method to generate brightγ-rays carrying large orbital angular momentum by interacting a circularly polarized Laguerre–Gaussian laser pulse with a near-critical hydrogen plasma co...We propose a new laser-plasma-based method to generate brightγ-rays carrying large orbital angular momentum by interacting a circularly polarized Laguerre–Gaussian laser pulse with a near-critical hydrogen plasma conflned in an over-dense solid tube.In the flrst stage of the interaction,it is found via fully relativistic three-dimensional particle-in-cell simulations that high-energy helical electron beams with large orbital angular momentum are generated.In the second stage,this electron beam interacts with the laser pulse reflected from the plasma disc behind the solid tube,and helicalγbeams are generated with the same topological structure as the electron beams.The results show that the electrons receive angular momentum from the drive laser,which can be further transferred to theγphotons during the interaction.Theγbeam orbital angular momentum is strongly dependent on the laser topological charge l and laser intensity a_(0),which scales as L_(γ)∝a_(0)~4.A short(duration of 5 fs)isolated helicalγbeam with an angular momentum of-3.3×10^(-14)kg m~2 s^(-1)is generated using the Laguerre–Gaussian laser pulse with l=2.The peak brightness of the helicalγbeam reaches 1.22×10^(24)photons s^(-1)mm^(-2)mrad^(-2)per 0.1%BW(at 10 Me V),and the laser-to-γ-ray angular momentum conversion rate is approximately 2.1%.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12375236 and 12135009)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDA25050100 and XDA25010100).
文摘The generation and reconnection of magneticflux ropes in a plasma irradiated by two Laguerre–Gaussian laser pulses with different frequen-cies and opposite topological charges are investigated numerically by particle-in-cell simulations.It is shown that twisted plasma currents and hence magneticflux ropes can be effectively generated as long as the laser frequency difference matches the electron plasma frequency.More importantly,subsequent reconnection of magneticflux ropes can occur.Typical signatures of magnetic reconnection,such as magnetic island formation and plasma heating,are identified in the reconnection of magneticflux ropes.Notably,it is found that a strong axial magneticfield can be generated on the axis,owing to the azimuthal current induced during the reconnection of the ropes.This indicates that in the reconnection of magneticflux ropes,the energy can be transferred not only from the magneticfield to the plasma but also from the plasma current back to the magneticfield.This work opens a new avenue to the study of magneticflux ropes,which helps in understanding magnetic topology changes,and resultant magnetic energy dissipation,plasma heating,and particle acceleration found in solarflares,and magnetic confinement fusion devices.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11974108 and 11574082)Fundamental Research Funds for the Central Universities (Grant No. 2021MS046)the Natural Science Foundation of Shandong Province, China (Grant No. ZR2019MA020)。
文摘We study the strong nonlinear optical dynamics of nanosecond pulsed Laguerre–Gaussian laser beams of high-order radial modes with zero orbital angular momentum propagating in the fullerene C60molecular medium. It is found that the spatiotemporal profile of the incident pulsed Laguerre–Gaussian laser beam is strongly reshaped during its propagation in the C60molecular medium. The centrosymmetric temporal profile of the incident pulse gradually evolves into a noncentrosymmetric meniscus shape, and the on-axis pulse duration is clearly depressed. Furthermore, the field intensity is distinctly attenuated due to the field-intensity-dependent reverse saturable absorption, and clear optical power limiting behavior is observed for different orders of the input pulsed Laguerre–Gaussian laser beams before the takeover of the saturation effect;the lower the order of the Laguerre–Gaussian beam, the lower the energy transmittance.
文摘We theoretically analyze the transient properties of a probe field absorption and dispersion in a coupled semiconductor double-quantum-dot nanostructure.We show that in the presence of the Gaussian laser beams,absorption and dispersion of the probe field can be dramatically influenced by the relative phase between applied fields and intensity of the Gaussian laser beams.Transient and steady-state behaviors of the probe field absorption and dispersion are discussed to estimate the required switching time.The estimated range is between 5-8 ps for subluminal to superluminal light propagation.
基金Supported by a financial grant from CSIR,New Delhi,India,under Project No.03(1277)/13/EMR-Ⅱ
文摘This paper presents an investigation on the self-focusing/defocusing of chirped Gaussian laser beam in collisional plasma with linear absorption. We have derived the differential equation for the beam width parameter by using WKB and paraxial approximations and solved it numerically. The effect of chirp and other laser plasma parameters is seen on the behavior of beam width parameter with dimensionless distance of propagation. The results are discussed and presented graphically. Our simulation results show that the amplitude of oscillations decreases with the distance of propagation. Due to collisional frequency, the laser beam shows fast divergence which can be minimized by the introduction of chirp parameter. The chirp decreases the effect of defocusing and increases the ability of self-focusing of laser beam in collisional plasma.
基金Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA25050300)the National Natural Science Foundation of China(Grant No.12205366)+2 种基金the National Key Research and Development Program of China(Grant No.2018YFA0404801)the Fundamental Research Funds for the Central Universities(Grant No.2020MS138)the Research Funds of Renmin University of China(Grant No.20XNLG01)。
文摘Laser-driven ion accelerators have the advantages of compact size,high density,and short bunch duration over conventional accelerators.Nevertheless,it is still challenging to generate ion beams with quasi-monoenergetic peak and low divergence in experiments with the current ultrahigh intensity laser and thin target technologies.Here we propose a scheme that a Laguerre–Gaussian laser irradiates a near-critical-density(NCD)plasma to generate a quasi-monoenergetic and low-divergence proton beam.The Laguerre–Gaussian laser pulse in an NCD plasma excites a moving longitudinal electrostatic field with a large amplitude,and it maintains the inward bowl-shape for dozens of laser durations.This special distribution of the longitudinal electrostatic field can simultaneously accelerate and converge the protons.Our particle-in-cell(PIC)simulation shows that the efficient proton acceleration can be realized with the Laguerre–Gaussian laser intensity ranging from 3.9×10^(21)W·cm^(-2)–1.6×10^(22)W·cm^(-2)available in the near future,e.g.,a quasi-monoenergetic proton beam with peak energy~115 MeV and divergence angles less than 5°can be generated by a 5.3×10^(21)W·cm^(-2)pulse.This work could provide a reference for the high-quality ion beam generation with PWclass laser systems available recently.
文摘The generation of terahertz(THz)waves via the beating of two high-intensity chirped Gaussian lasers in a multi-ion-species plasma is numerically studied by taking into account the weak relativistic and ponderomotive regime of interaction.The coupled differential equations for beamwidth parameters are extracted by introducing the dielectric function of such plasma and using WKB and paraxial ray approximations.The amplitude of THz radiation at beat frequency resulting from the nonlinear current density induced by the beat ponderomotive force of the cross-focusing of beams was obtained.The impacts of the chirp frequency parameter,initial laser intensity and initial ionic species density(specifically,the presence of singly and doubly charged ions)in the plasma on THz generation were discussed.Our numerical results reveal that THz radiation generation strongly depends on the chirp frequency parameter.A specific range of chirp frequencies exists for self-focusing as well as THz generation with a'turning point',where the THz emission reaches its maximum value.The results show that the strength of self-focusing and consequently the generated THz radiation are reduced by increasing the density of doubly charged ionic species in the plasma due to the suppression of the nonlinear effects.
文摘This work reveals an exploration of self-focusing of Hermite-cosine-Gaussian laser beam in a collisionless plasma under relativistic nonlinearity. Self-focusing along with self-trapping of Hermite-cosine-Gaussian laser beam are analyzed for different values of laser intensity, plasma density, and decentered parameters. Mathematical analysis displays that these parameters play a major role in achieving the stronger and earlier self-focusing. Further, a comparative study between self-focusing of Hermite-cosine-Gaussian laser beam with and without exponential density ramp profile is introduced. Plasma density transition with exponential profile is found to be more effective in order to have stronger self-focusing. The present analysis may lead to very useful applications in the field of efficient harmonic generation, laser driven fusion etc.
文摘The present paper is aimed to study the effect of Gaussian laser light on first and second sound waves in superfluid helium theoretically using optoacoustic method. The mechanism applied in this study is electrostriction mechanism. This study considers crystal parts of superfluid helium with a zero absorption coefficient applying electrostriction mechanism. Affecting Gaussian laser light on these crystal parts, a spectrum of cylindrical first and second sound waves and cylindrical slow and rapid waves is obtained. Meanwhile, frequency of waves amplitudes proportionate to time period of laser light is calculated.
文摘We present in this paper an investigation of the nonlinear process of above-threshold ionization. The process arises when an atomic or molecular system, exposed to an intense laser pulse, continues to absorb more photons than that needed for the ionization to occur. We trigger this nonlinear process in a simple molecular system by exposing it to an intense transform-limited Gaussian laser pulse of 267-nm wavelength which is the third harmonic of an 800-nm wavelength Tisapphire laser. We explore the characteristics of the process by analyzing the kinetic-energy spectra of the electrons ejected from the molecular system under different laser peak intensities.
基金supported by the National Natural Science Foundation of China(grant number 12075306)Strategic Priority Research Program of the Chinese Academy of Sciences(grant number XDB16010600)+4 种基金Key Research Programs in Frontier Science(grant number ZDBSLY-SLH006)Shanghai special science and technology innovation supported project(grant number 2019-jmrh1-kj1)Advanced research using high-intensity laser-produced photons and particles(ADONISgrant number CZ.02.1.01/0.0/0.0/16019/0000789)and High Field Initiative(HiFI,grant number CZ.02.1.01/0.0/0.0/15003/0000449)financial support of the Ministry of Education,Youth and Sports as part of targeted support from the National Programme of Sustainability Ⅱ。
文摘A new near-infrared direct acceleration mechanism driven by Laguerre-Gaussian laser is proposed to stably accelerate and concentrate electron slice both in longitudinal and transversal directions in vacuum.Three-dimensional simulations show that a 2-μm circularly polarized LG_(p)^(l)(p=0,l=1,σ_(2)=-1)laser can directly manipulate attosecond electron slices in additional dimensions(angular directions)and give them annular structures and angular momentums.These annular vortex attosecond electron slices are expected to have some novel applications such as in the collimation of antiprotons in conventional linear accelerators,edge-enhancement electron imaging,structured X-ray generation,and analysis and manipulation of nanomaterials.
文摘In this paper, according to the temperature and strain distribution obtained by considering the Gaussian pump profile and dependence of physical properties on temperature, we derive an analytical model for refractive index variations of the diode side-pumped Nd：YAG laser rod. Then we evaluate this model by numerical solution and our maximum relative errors are 5% and 10% for variations caused by thermo–optical and thermo–mechanical effects; respectively. Finally, we present an analytical model for calculating the focal length of the thermal lens and spherical aberration. This model is evaluated by experimental results.
文摘Laser transformation hardening(LTH) is one of the laser surface modification processes.The surface hardening of rod-shaped carbon steel(SM45C) was performed by lathe-based laser composite processor with Gaussian-beam optical head.The LTH characteristics by dominant processes,longitudinal and depth directional hardness distributions and behaviors of phase transformation in hardened zones were examined.Especially,two concepts of circumferential speed and theoretical overlap rate were applied.When laser power increased or circumferential speed decreased,the surface hardening depth gradually increases due to the increased heat input.Moreover,the longitudinal hardness distribution particularly shows periodicity of repetitive increase and decrease,which results from tempering effect by overlap.Finally,the feasibility of laser transformation hardening is verified by using the beam with Gaussian intensity distribution.
文摘A single-mode laser system with non-Gaussian and Gaussian noise is investigated. The stationary mean value and the normalized variance of the laser intensity are numerically calculated under the condition that the stationary probability distribution function （SPDF） is derived. The SPDF as a function of the laser intensity exhibits a maximum, The maximum becomes smaller with the increase of the correlation intensity or the non-Gaussian parameter, where the later is a measure of the deviation from the Gaussian characteristic. The maximum becomes larger as the correlation time increases. The laser intensity stationary mean value decreases with the increase of the correlation intensity or the non-Gaussian parameter while increases with the correlation time increasing. The laser intensity normalized variance increases with the increase of the correlation intensity or the non-Gaussian parameter while decreases as the correlation time increases.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11374209,11374210,and 11774227)the Major State Basic Research Development Program of China(Grant No.2015CB859700)
文摘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.
基金Project supported by the National Natural Science Foundation of China(Grant No.10774039)the Basic Research Program of Education Bureau of Henan Province of China(Grant No.072300410130)
文摘Using time-dependent multilevel approach （TDML）, this paper studies the dynamics of coherent control of Rydberg lithium atoms and demonstrates that Rydberg lithium atoms can be transferred to states of higher principal quantum number by exposing them to specially designed frequency-chirped laser pulses. The population transfer from n=70 to n=75 states of lithium atoms with efficiency more than 90% is achieved by means of the sequential adiabatic rapid passages. The results agree well with the experimental ones and show that the coherent control of the population transfer from the lower n to the higher n states can be accomplished by the optimization of the chirping parameters and the intensity of laser field.
文摘激光无线传能(Laser Wireless Power Transmission,LWPT)系统中,传能激光光束质量直接影响传能效率,为了提高传能光束质量,提出了一种基于反高斯算法的激光光场匀化策略:首先建立激光光束的高斯数学模型,进而求出该高斯函数的反函数,得到对应的反高斯函数,再将该高斯函数与反高斯函数相乘,则得到一个常数。由此表明,高斯激光光束通过反高斯处理后,可以实现匀化;基于该策略,设计了反高斯光场匀化方案置,以此构建了基于反高斯匀化的激光无线传能系统模型。仿真实验结果表明,反高斯匀化策略与现有的激光光束整形方法相比,在不依赖复杂光学元件组与加工精度要求的前提下,光束发散角为6 mrad,光强均匀度达到了83%。由此可见,匀化效果明显,为激光无线传能系统效率提升提供了新的解决方案。
基金flnancially supported by National Natural Science Foundation of China(Nos.11664039,11964038,12104428,and 11875007)support from the Young Talents Project at Ocean University of China。
文摘We propose a new laser-plasma-based method to generate brightγ-rays carrying large orbital angular momentum by interacting a circularly polarized Laguerre–Gaussian laser pulse with a near-critical hydrogen plasma conflned in an over-dense solid tube.In the flrst stage of the interaction,it is found via fully relativistic three-dimensional particle-in-cell simulations that high-energy helical electron beams with large orbital angular momentum are generated.In the second stage,this electron beam interacts with the laser pulse reflected from the plasma disc behind the solid tube,and helicalγbeams are generated with the same topological structure as the electron beams.The results show that the electrons receive angular momentum from the drive laser,which can be further transferred to theγphotons during the interaction.Theγbeam orbital angular momentum is strongly dependent on the laser topological charge l and laser intensity a_(0),which scales as L_(γ)∝a_(0)~4.A short(duration of 5 fs)isolated helicalγbeam with an angular momentum of-3.3×10^(-14)kg m~2 s^(-1)is generated using the Laguerre–Gaussian laser pulse with l=2.The peak brightness of the helicalγbeam reaches 1.22×10^(24)photons s^(-1)mm^(-2)mrad^(-2)per 0.1%BW(at 10 Me V),and the laser-to-γ-ray angular momentum conversion rate is approximately 2.1%.
