Effect of critical beam radius on self-focusing of cosh-Gaussian laser beams in collisionless magnetized plasma under ponderomotive nonlinearity forms the main core of present work. To investigate propagation dynamics...Effect of critical beam radius on self-focusing of cosh-Gaussian laser beams in collisionless magnetized plasma under ponderomotive nonlinearity forms the main core of present work. To investigate propagation dynamics of cosh-Gaussian laser beams in collisionless magnetized plasma, well established parabolic equation approach under WKB and paraxial approximations is employed. Our study is crucially pivoted on the concept of critical curve and subsequent determination of numerical interval for decentered parameter to sustain the competition between diffraction and self-focusing during the propagation of laser beam. Additionally, in the present study an interesting feature in the self-focusing region of the critical curve has been attempted for different values of decentered parameter.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
Density transition based self-focusing of cosh-Gaussian laser beam in plasma with linear absorption has been studied. The field distribution in the plasma is expressed in terms of beam width parameter, decentered para...Density transition based self-focusing of cosh-Gaussian laser beam in plasma with linear absorption has been studied. The field distribution in the plasma is expressed in terms of beam width parameter, decentered parameter,and linear absorption coefficient. The differential equation for the beam width parameter is solved by following Wentzel–Kramers–Brillouin(WKB) and paraxial approximation through parabolic wave equation approach. The behaviour of beam width parameter with dimensionless distance of propagation is studied at optimum values of plasma density,decentered parameter and with different absorption levels in the medium. The results reveal that these parameters can affect the self-focusing significantly.展开更多
The propagation of quadruple Gaussian laser beam in a plasma characterized by axial inhomogeneity and nonlinearity due to ponderomotive force in the paraxial ray approximation is investigated.An appropriate expression...The propagation of quadruple Gaussian laser beam in a plasma characterized by axial inhomogeneity and nonlinearity due to ponderomotive force in the paraxial ray approximation is investigated.An appropriate expression for the nonlinear dielectric constant has been developed in the presence of external magnetic field,with linear absorption and due to saturation effects for arbitrary large intensity.The effects of different types of plasma axial inhomogeneities on self-focusing of laser beam have been studied with the typical laser and plasma parameters.Self-focusing of quadruple Gaussian laser beam in the presence of externally applied magnetic field and saturating parameter is found significantly improved in the case of extraordinary mode.Our results reveal that initially converging beam shows oscillatory convergence whereas initially diverging beam shows oscillatory divergence.The beam is more focussed at lower intensity in both cases viz.extraordinary and ordinary mode.展开更多
The Max’s equation of self-focusing in laser-plasma interaction due to the pondermotive force has been discussed and its physical meaning of the assumption has been predicted. The characteristics of selffocusing due ...The Max’s equation of self-focusing in laser-plasma interaction due to the pondermotive force has been discussed and its physical meaning of the assumption has been predicted. The characteristics of selffocusing due to the pondermotive force with different initial situations have been analyzed through the numerical calculation.展开更多
Self-compression of femtosecond pulses in noble gases with an input power close to the self-focusing threshold has been investigated experimentally and theoretically. It is demonstrated that either multiphoton ionizat...Self-compression of femtosecond pulses in noble gases with an input power close to the self-focusing threshold has been investigated experimentally and theoretically. It is demonstrated that either multiphoton ionization （MPI） or space-time focusing and self-steepening effects can induce pulse shortening, but they predominate at different beam intensities during the propagation. The latter effects play a key role in the final pulse self-compression. By choosing an appropriate focusing parameter, action distance of the space-time focusing and self-steepening effects can be lengthened, which can promote a shock pulse structure with a duration as short as two optical cycles. It is also found that, for our calculation cases in which an input pulse power is close to the self-focusing threshold, either group velocity dispersion （GVD） or multiphoton absorption （MPA） has a negligible influence on pulse characteristics in the propagation process.展开更多
The influence of a self-focused beam on the stimulated Raman scattering(SRS)process in collisional plasma is explored.Here,collisional nonlinearity arises as a result of non-uniform heating,thereby causing carrier red...The influence of a self-focused beam on the stimulated Raman scattering(SRS)process in collisional plasma is explored.Here,collisional nonlinearity arises as a result of non-uniform heating,thereby causing carrier redistribution.The plasma density profile gets modified in a perpendicular direction to the main beam axis.This modified plasma density profile greatly affects the pump wave,electron plasma wave(EPW)and back-scattered wave.The well-known paraxial theory and Wentzel-Kramers-Brillouin approximation are used to derive second-order ordinary differential equations for the beam waists of the pump wave,EPW and the scattered wave.Further to this,the well-known fourth-order Runge-Kutta method is used to carry out numerical simulations of these equations.SRS back-reflectivity is found to increase due to the focusing of several waves involved in the process.展开更多
This paper presents an investigation of weakly relativistic ponderomotive effects on self-focusing during interaction of high power elliptical laser beam with plasma. The nonlinear differential equations for the beam ...This paper presents an investigation of weakly relativistic ponderomotive effects on self-focusing during interaction of high power elliptical laser beam with plasma. The nonlinear differential equations for the beam width parameters of elliptical laser beam have set up by using Wentzal–Krammers–Brillouin(WKB) and paraxial approximations. These equations have been solved numerically by using fourth order Runge–Kutta method to study the variation of these beam width parameters against normalized distance of propagation. Effects of variation in laser beam intensity,plasma density and electron temperature on the beam width parameters are also analyzed.展开更多
Transverse localization of light is investigated numerically in a serf-focusing Kerr medium with a complex-valued optical lattice featuring parity-time symmetry. It is demonstrated that the light localization exists b...Transverse localization of light is investigated numerically in a serf-focusing Kerr medium with a complex-valued optical lattice featuring parity-time symmetry. It is demonstrated that the light localization exists below the threshold of the spatial frequency of the lattices, and is further enhanced with the decrease of the spatial frequency. The influence of defects on the transverse localization is also discussed in detail. The results show that both positive and negative defects in such a medium would enhance the localization.展开更多
In the present manuscript,we analyse the effect of exponential plasma density ramp for relativistic selffocusing of Hermite-cosh-Gaussian laser pulse in magnetoplasma.The exponential plasma density ramp is found to be...In the present manuscript,we analyse the effect of exponential plasma density ramp for relativistic selffocusing of Hermite-cosh-Gaussian laser pulse in magnetoplasma.The exponential plasma density ramp is found to be more prominent in achieving the stronger self-focusing of Hermite-cosh-Gaussian laser beam in comparison to the tangential plasma density ramp.We propose a theoretical model for propagation of Hermite-cosh-Gaussian laser pulse in magnetoplasma with exponential density ramp.The nonlinearity in the medium arises because of the relativistic motion of electrons,being responsible for relativistic self-focusing.Equation of the beam width parameter is set up by taking the expression for the dielectric function and following Wentzel-Kramers-Brillouin(WKB)with paraxial ray approximations for mode indices m=0,1 and 2.Effect of decentered parameter is also analysed,which results in stronger self-focusing of the Hermite-cosh-Gaussian laser beam.Stronger self-focusing of laser beam is more pronounced in high density plasma with higher magnetic field.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
Effect of higher order axial electron temperature on self-focusing of electromagnetic pulsed beam in collisional plasma is investigated.It is shown that higher order axial electron temperature T p4 is not trivial than...Effect of higher order axial electron temperature on self-focusing of electromagnetic pulsed beam in collisional plasma is investigated.It is shown that higher order axial electron temperature T p4 is not trivial than T p0 and T p2,which can modify slightly radial redistribution of electron density and increases effective dielectric constant.As a result,on one hand,slightly reduce electromagnetic beam self-focusing in the course of oscillatory convergence,on the other hand,quicken beam divergence in the course of steady divergence,i.e.,higher order axial electron temperature T p4 can decrease the influence of collisional nonlinearity in collisional plasma.展开更多
Here we report on a simple-to-implement and cost-effective approach for laser pulse contrast enhancement,based on the χ(3)nonlinear self-focusing effect.An intentionally induced and gently controlled self-focusing in...Here we report on a simple-to-implement and cost-effective approach for laser pulse contrast enhancement,based on the χ(3)nonlinear self-focusing effect.An intentionally induced and gently controlled self-focusing in a thin glass transforms the time-dependent intensity into variation in beam divergence.Followed by a spatial discriminating filter,only the strongly focused fraction traverses the setup,at the expense of efficiency.A numerical model,accounting for the pulse and material parameters via a Gaussian ABCD matrix,provides an estimate for the instantaneous beam waist and transmission efficiency,which enables us to evaluate the resulting contrast enhancement.The estimated contrast enhancement spans between 0.5 and 2.5 orders of magnitude,in conjunction with approximately 25%–90%estimated efficiency,depending on the pulse parameters.In a preliminary experiment we demonstrated the effect with 10s-μJ sub GW regime with approximately 40%efficiency and a contrast improvement of more than or equal to 20 dB.展开更多
Based on the paraxial wave equation,this study extends the theory of small-scale self-focusing(SSSF)from coherent beams to spatially partially coherent beams(PCBs)and derives a general theoretical equation that reveal...Based on the paraxial wave equation,this study extends the theory of small-scale self-focusing(SSSF)from coherent beams to spatially partially coherent beams(PCBs)and derives a general theoretical equation that reveals the underlying physics of the reduction in the B-integral of spatially PCBs.From the analysis of the simulations,the formula for the modulational instability(MI)gain coefficient of the SSSF of spatially PCBs is obtained by introducing a decrease factor into the formula of the MI gain coefficient of the SSSF of coherent beams.This decrease can be equated to a drop in the injected light intensity or an increase in the critical power.According to this formula,the reference value of the spatial coherence of spatially PCBs is given,offering guidance to overcome the output power limitation of the high-power laser driver due to SSSF.展开更多
A novel method,combining an asymmetric four-grating compressor(AFGC)with pulse post-compression,is numerically demonstrated to improve the spatial uniformity of laser beams and hence to suppress small-scale self-focus...A novel method,combining an asymmetric four-grating compressor(AFGC)with pulse post-compression,is numerically demonstrated to improve the spatial uniformity of laser beams and hence to suppress small-scale self-focusing(SSSF)during the beam propagation in nonlinear materials of high peak power lasers.The spatial uniformity of laser beams is an important factor in performing post-compression,due to the spatial intensity modulation,or hot spots will be aggravated during the nonlinear propagation and then seriously damage the subsequent optical components.Three-dimensional numerical simulations of post-compression are implemented based on a femtosecond laser with a standard compressor and an AFGC,respectively.The simulated results indicate that post-compression with the AFGC can efficiently suppress the SSSF and also shorten the laser pulses from 30 fs to sub-10 fs.This work can provide a promising route to overcome the challenge of SSSF and will be meaningful to promote the practical application of the post-compression technique in high peak power lasers.展开更多
A ground-based laser system for space-debris cleaning will use powerful laser pulses that can self-focus while propagating through the atmosphere.We demonstrate that for the relevant laser parameters,this self-focusin...A ground-based laser system for space-debris cleaning will use powerful laser pulses that can self-focus while propagating through the atmosphere.We demonstrate that for the relevant laser parameters,this self-focusing can noticeably decrease the laser intensity on the target.We show that the detrimental effect can be,to a great extent,compensated for by applying the optimal initial beam defocusing.The effect of laser elevation on the system performance is discussed.展开更多
Acoustic wave time reversal self-focusing in underwater waveguide is studied. The acoustic wave time reversal is theoretically and experimentally investigated in a half-infinite fluid medium and a shallow fluid layer ...Acoustic wave time reversal self-focusing in underwater waveguide is studied. The acoustic wave time reversal is theoretically and experimentally investigated in a half-infinite fluid medium and a shallow fluid layer placed on a hard half-infinite solid medium, respectively. The ray approach method is adopted to study the far field of the acoustic field in theory, and the ultrasonic experiments have been carried out in laboratory to model the underwater waveguide. It is shown by theoretical and experimental results that the focusing gain can be improved by 12 dB or more.展开更多
By ‘‘seeing" the green two-photon luminescence, two separate focusing points are observed on the propagation axis of a converging femtosecond laser beam in a ZnO single crystal rod. It is found that the selffoc...By ‘‘seeing" the green two-photon luminescence, two separate focusing points are observed on the propagation axis of a converging femtosecond laser beam in a ZnO single crystal rod. It is found that the selffocusing effect makes a significant contribution to the formation of the first focusing point, while the second focusing point is caused by self-refocusing. The position of the first focusing point is in good agreement with the value predicted by a model developed by Chin and his co-workers. These experimental findings could be the unprecedented evidence for the self-focusing and refocusing effect of the femtosecond laser filament propagation in nonlinear media.展开更多
A linearization model was used to analyze the laser beam propagation in a high power laser driver and the influence of the small-scale self-focusing and spatial phase noise on beam quality in disk amplifiers. The quan...A linearization model was used to analyze the laser beam propagation in a high power laser driver and the influence of the small-scale self-focusing and spatial phase noise on beam quality in disk amplifiers. The quantitative relations between intensities of spatial phase noise, B-integral, and beam intensity contrast in near field are given explicitly. A spectrum specification of phase noise has been obtained by setting a limit to the contrast of an output beam.展开更多
The self-focusing phenomenon of partially coherent beams(PCBs)was simulated using the complex screen method combined with the split-step Fourier method to solve the nonlinear Schrödinger equation.Considering the ...The self-focusing phenomenon of partially coherent beams(PCBs)was simulated using the complex screen method combined with the split-step Fourier method to solve the nonlinear Schrödinger equation.Considering the propagation of Gaussian Schell-model beams in a nonlinear medium as an example,the suppression effects of intensity,propagation distance,and spatial coherence on small-scale self-focusing were demonstrated.Simulations of overall and small-scale self-focusing using this method were compared with the existing literature to demonstrate the validity of the method.This method can numerically analyze the degree of self-focusing in PCBs and advance the study of their nonlinearity.展开更多
文摘Effect of critical beam radius on self-focusing of cosh-Gaussian laser beams in collisionless magnetized plasma under ponderomotive nonlinearity forms the main core of present work. To investigate propagation dynamics of cosh-Gaussian laser beams in collisionless magnetized plasma, well established parabolic equation approach under WKB and paraxial approximations is employed. Our study is crucially pivoted on the concept of critical curve and subsequent determination of numerical interval for decentered parameter to sustain the competition between diffraction and self-focusing during the propagation of laser beam. Additionally, in the present study an interesting feature in the self-focusing region of the critical curve has been attempted for different values of decentered parameter.
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.
基金Supported by a Financial Grant from CSIR,New Delhi,India,under Project No.03(1277)/13/EMR-II
文摘Density transition based self-focusing of cosh-Gaussian laser beam in plasma with linear absorption has been studied. The field distribution in the plasma is expressed in terms of beam width parameter, decentered parameter,and linear absorption coefficient. The differential equation for the beam width parameter is solved by following Wentzel–Kramers–Brillouin(WKB) and paraxial approximation through parabolic wave equation approach. The behaviour of beam width parameter with dimensionless distance of propagation is studied at optimum values of plasma density,decentered parameter and with different absorption levels in the medium. The results reveal that these parameters can affect the self-focusing significantly.
文摘The propagation of quadruple Gaussian laser beam in a plasma characterized by axial inhomogeneity and nonlinearity due to ponderomotive force in the paraxial ray approximation is investigated.An appropriate expression for the nonlinear dielectric constant has been developed in the presence of external magnetic field,with linear absorption and due to saturation effects for arbitrary large intensity.The effects of different types of plasma axial inhomogeneities on self-focusing of laser beam have been studied with the typical laser and plasma parameters.Self-focusing of quadruple Gaussian laser beam in the presence of externally applied magnetic field and saturating parameter is found significantly improved in the case of extraordinary mode.Our results reveal that initially converging beam shows oscillatory convergence whereas initially diverging beam shows oscillatory divergence.The beam is more focussed at lower intensity in both cases viz.extraordinary and ordinary mode.
文摘The Max’s equation of self-focusing in laser-plasma interaction due to the pondermotive force has been discussed and its physical meaning of the assumption has been predicted. The characteristics of selffocusing due to the pondermotive force with different initial situations have been analyzed through the numerical calculation.
基金supported by the National Basic Research Program of China (Grant No 2006CB806000)the National Natural Science Foundation of China (Grant Nos 60578049 and 10523003)the Science and Technology Commission of Shanghai Municipality of China (Grant No 07JC14055)
文摘Self-compression of femtosecond pulses in noble gases with an input power close to the self-focusing threshold has been investigated experimentally and theoretically. It is demonstrated that either multiphoton ionization （MPI） or space-time focusing and self-steepening effects can induce pulse shortening, but they predominate at different beam intensities during the propagation. The latter effects play a key role in the final pulse self-compression. By choosing an appropriate focusing parameter, action distance of the space-time focusing and self-steepening effects can be lengthened, which can promote a shock pulse structure with a duration as short as two optical cycles. It is also found that, for our calculation cases in which an input pulse power is close to the self-focusing threshold, either group velocity dispersion （GVD） or multiphoton absorption （MPA） has a negligible influence on pulse characteristics in the propagation process.
文摘The influence of a self-focused beam on the stimulated Raman scattering(SRS)process in collisional plasma is explored.Here,collisional nonlinearity arises as a result of non-uniform heating,thereby causing carrier redistribution.The plasma density profile gets modified in a perpendicular direction to the main beam axis.This modified plasma density profile greatly affects the pump wave,electron plasma wave(EPW)and back-scattered wave.The well-known paraxial theory and Wentzel-Kramers-Brillouin approximation are used to derive second-order ordinary differential equations for the beam waists of the pump wave,EPW and the scattered wave.Further to this,the well-known fourth-order Runge-Kutta method is used to carry out numerical simulations of these equations.SRS back-reflectivity is found to increase due to the focusing of several waves involved in the process.
文摘This paper presents an investigation of weakly relativistic ponderomotive effects on self-focusing during interaction of high power elliptical laser beam with plasma. The nonlinear differential equations for the beam width parameters of elliptical laser beam have set up by using Wentzal–Krammers–Brillouin(WKB) and paraxial approximations. These equations have been solved numerically by using fourth order Runge–Kutta method to study the variation of these beam width parameters against normalized distance of propagation. Effects of variation in laser beam intensity,plasma density and electron temperature on the beam width parameters are also analyzed.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11104185,11174084,10934011 and 11504236the National Basic Research Program of China under Grant No 2012CB921904+1 种基金the Innovation Program of Shanghai Municipal Education Commission under Grant No 11YZ118the Natural Science Foundation of Shanghai under Grant No 14ZR1414300
文摘Transverse localization of light is investigated numerically in a serf-focusing Kerr medium with a complex-valued optical lattice featuring parity-time symmetry. It is demonstrated that the light localization exists below the threshold of the spatial frequency of the lattices, and is further enhanced with the decrease of the spatial frequency. The influence of defects on the transverse localization is also discussed in detail. The results show that both positive and negative defects in such a medium would enhance the localization.
文摘In the present manuscript,we analyse the effect of exponential plasma density ramp for relativistic selffocusing of Hermite-cosh-Gaussian laser pulse in magnetoplasma.The exponential plasma density ramp is found to be more prominent in achieving the stronger self-focusing of Hermite-cosh-Gaussian laser beam in comparison to the tangential plasma density ramp.We propose a theoretical model for propagation of Hermite-cosh-Gaussian laser pulse in magnetoplasma with exponential density ramp.The nonlinearity in the medium arises because of the relativistic motion of electrons,being responsible for relativistic self-focusing.Equation of the beam width parameter is set up by taking the expression for the dielectric function and following Wentzel-Kramers-Brillouin(WKB)with paraxial ray approximations for mode indices m=0,1 and 2.Effect of decentered parameter is also analysed,which results in stronger self-focusing of the Hermite-cosh-Gaussian laser beam.Stronger self-focusing of laser beam is more pronounced in high density plasma with higher magnetic field.
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.
文摘Effect of higher order axial electron temperature on self-focusing of electromagnetic pulsed beam in collisional plasma is investigated.It is shown that higher order axial electron temperature T p4 is not trivial than T p0 and T p2,which can modify slightly radial redistribution of electron density and increases effective dielectric constant.As a result,on one hand,slightly reduce electromagnetic beam self-focusing in the course of oscillatory convergence,on the other hand,quicken beam divergence in the course of steady divergence,i.e.,higher order axial electron temperature T p4 can decrease the influence of collisional nonlinearity in collisional plasma.
文摘Here we report on a simple-to-implement and cost-effective approach for laser pulse contrast enhancement,based on the χ(3)nonlinear self-focusing effect.An intentionally induced and gently controlled self-focusing in a thin glass transforms the time-dependent intensity into variation in beam divergence.Followed by a spatial discriminating filter,only the strongly focused fraction traverses the setup,at the expense of efficiency.A numerical model,accounting for the pulse and material parameters via a Gaussian ABCD matrix,provides an estimate for the instantaneous beam waist and transmission efficiency,which enables us to evaluate the resulting contrast enhancement.The estimated contrast enhancement spans between 0.5 and 2.5 orders of magnitude,in conjunction with approximately 25%–90%estimated efficiency,depending on the pulse parameters.In a preliminary experiment we demonstrated the effect with 10s-μJ sub GW regime with approximately 40%efficiency and a contrast improvement of more than or equal to 20 dB.
文摘Based on the paraxial wave equation,this study extends the theory of small-scale self-focusing(SSSF)from coherent beams to spatially partially coherent beams(PCBs)and derives a general theoretical equation that reveals the underlying physics of the reduction in the B-integral of spatially PCBs.From the analysis of the simulations,the formula for the modulational instability(MI)gain coefficient of the SSSF of spatially PCBs is obtained by introducing a decrease factor into the formula of the MI gain coefficient of the SSSF of coherent beams.This decrease can be equated to a drop in the injected light intensity or an increase in the critical power.According to this formula,the reference value of the spatial coherence of spatially PCBs is given,offering guidance to overcome the output power limitation of the high-power laser driver due to SSSF.
基金supported by the National Key R&D Program of China(2022YFE0204800,2022YFA1604401,2019YFF01014401)Shanghai Sailing Program(21YF1453800)+5 种基金National Natural Science Foundation of China(11127901,61925507)International Partnership Program of Chinese Academy of Sciences(181231KYSB20200040)Shanghai Science and Technology Committee Program(22560780100,23560750200)Chinese Academy of Sciences President’s International Fellowship Initiative(2023VMB0008)Ministry of Science and Higher Education of the Russian Federation(075-15-2020-906,Center of Excellence‘Center of Photonics’)Youth Innovation Promotion Association of the Chinese Academy of Sciences。
文摘A novel method,combining an asymmetric four-grating compressor(AFGC)with pulse post-compression,is numerically demonstrated to improve the spatial uniformity of laser beams and hence to suppress small-scale self-focusing(SSSF)during the beam propagation in nonlinear materials of high peak power lasers.The spatial uniformity of laser beams is an important factor in performing post-compression,due to the spatial intensity modulation,or hot spots will be aggravated during the nonlinear propagation and then seriously damage the subsequent optical components.Three-dimensional numerical simulations of post-compression are implemented based on a femtosecond laser with a standard compressor and an AFGC,respectively.The simulated results indicate that post-compression with the AFGC can efficiently suppress the SSSF and also shorten the laser pulses from 30 fs to sub-10 fs.This work can provide a promising route to overcome the challenge of SSSF and will be meaningful to promote the practical application of the post-compression technique in high peak power lasers.
基金This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344The support of the ERC and the grant from the Ministry of Education and Science of the Russian Federation(agreement no.14.B25.31.0003)are acknowledged.
文摘A ground-based laser system for space-debris cleaning will use powerful laser pulses that can self-focus while propagating through the atmosphere.We demonstrate that for the relevant laser parameters,this self-focusing can noticeably decrease the laser intensity on the target.We show that the detrimental effect can be,to a great extent,compensated for by applying the optimal initial beam defocusing.The effect of laser elevation on the system performance is discussed.
基金This work was supported by the National Natural Science Foundation of China (19634050, 10134020).
文摘Acoustic wave time reversal self-focusing in underwater waveguide is studied. The acoustic wave time reversal is theoretically and experimentally investigated in a half-infinite fluid medium and a shallow fluid layer placed on a hard half-infinite solid medium, respectively. The ray approach method is adopted to study the far field of the acoustic field in theory, and the ultrasonic experiments have been carried out in laboratory to model the underwater waveguide. It is shown by theoretical and experimental results that the focusing gain can be improved by 12 dB or more.
基金financially supported by Shenzhen Municipal Science and Technology Innovation Council (JCYJ20170818141709893)National Natural Science Foundation of China (11374247)Hong Kong RGC-GRF Grant (HKU 705812P)
文摘By ‘‘seeing" the green two-photon luminescence, two separate focusing points are observed on the propagation axis of a converging femtosecond laser beam in a ZnO single crystal rod. It is found that the selffocusing effect makes a significant contribution to the formation of the first focusing point, while the second focusing point is caused by self-refocusing. The position of the first focusing point is in good agreement with the value predicted by a model developed by Chin and his co-workers. These experimental findings could be the unprecedented evidence for the self-focusing and refocusing effect of the femtosecond laser filament propagation in nonlinear media.
基金This work is partially supported by the Key Project of the National Natural Science Foundation of China (Grant No. 69789801) the Team Project of Natural Science Foundation of Guangdong Province (Grant No. 20003061) the Funds of National Hi-Tech Committee
文摘A linearization model was used to analyze the laser beam propagation in a high power laser driver and the influence of the small-scale self-focusing and spatial phase noise on beam quality in disk amplifiers. The quantitative relations between intensities of spatial phase noise, B-integral, and beam intensity contrast in near field are given explicitly. A spectrum specification of phase noise has been obtained by setting a limit to the contrast of an output beam.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Nos.XDA25020203 and 25020301)the Innovation Fund of the Key Laboratory of the Chinese Academy of Sciences(No.CXJJ-21S015)。
文摘The self-focusing phenomenon of partially coherent beams(PCBs)was simulated using the complex screen method combined with the split-step Fourier method to solve the nonlinear Schrödinger equation.Considering the propagation of Gaussian Schell-model beams in a nonlinear medium as an example,the suppression effects of intensity,propagation distance,and spatial coherence on small-scale self-focusing were demonstrated.Simulations of overall and small-scale self-focusing using this method were compared with the existing literature to demonstrate the validity of the method.This method can numerically analyze the degree of self-focusing in PCBs and advance the study of their nonlinearity.
