Synthesis of multi-color laser pulses has been developed as a promising way to improve low conversion efficiency of high-order harmonic generation(HHG). Here we systematically study the effect of laser focus in a two-...Synthesis of multi-color laser pulses has been developed as a promising way to improve low conversion efficiency of high-order harmonic generation(HHG). Here we systematically study the effect of laser focus in a two-color waveform on generation of macroscopic HHG in soft x-rays. We find that the dependence of HHG yields on laser focus at low or high gas pressure is sensitive to the characteristics of single-atom harmonic response, in which “short”-or “long”-trajectory emissions can be selectively controlled by changing the waveform of two-color synthesized laser pulse. We uncover the phase-matching mechanism of HHG in the gas medium by examining the propagation of the two-color waveform and the evolution of time-frequency emissions of high-harmonic field. We further reveal that the nonlinear effects, such as geometric phase, atomic dispersion, and plasma defocusing, are responsible for modification of two-color waveform upon propagation. This work can be used to find better macroscopic conditions for generating soft x-ray HHG by employing two-color optimized waveforms.展开更多
Laser-induced breakdown spectroscopy(LIBS)is a capable technique for elementary analysis,while LIBS quantitation is still under development.In quantitation,precise laser focusing plays an important role because it ens...Laser-induced breakdown spectroscopy(LIBS)is a capable technique for elementary analysis,while LIBS quantitation is still under development.In quantitation,precise laser focusing plays an important role because it ensures the distance between the laser and samples.In the present work,we employed spectral intensity as a direct way to assist laser focusing in LIBS quantitation for copper alloys.It is found that both the air emission and the copper line could be used to determine the position of the sample surface by referencing the intensity maximum.Nevertheless,the fine quantitation was only realized at the position where the air emission(e.g.O(I)777.4 nm)reached intensity maximum,and also in this way,a repeatable quantitation was successfully achieved even after 120 days.The results suggested that the LIBS quantitation was highly dependent on the focusing position of the laser,and spectra-assisted focusing could be a simple way to find the identical condition for different samples’detection.In the future,this method might be applicable in field measurements for LIBS analysis of solids.展开更多
Laser focused atomic deposition is a unique and effective way to fabricate highly accurate pitch standards in nanometrology.However,the stability and repeatability of the atom lithography fabrication process remains a...Laser focused atomic deposition is a unique and effective way to fabricate highly accurate pitch standards in nanometrology.However,the stability and repeatability of the atom lithography fabrication process remains a challenging problem for massive production.Based on the atom-light interaction theory,channeling is utilized to improve the stability and repeatability.From the comparison of three kinds of atom-light interaction models,the optimal parameters for channeling are obtained based on simulation.According to the experimental observations,the peak to valley height of Cr nano-gratings keeps stable when the cutting proportion changes from 15%to 50%,which means that the channeling shows up under this condition.The channeling proves to be an effective method to optimize the stability and repeatability of laser focused Cr atomic deposition.展开更多
This paper presents a novel view of the impact of electron collision off-axis positions on the dynamic properties and relativistic nonlinear Thomson inverse scattering of excited electrons within tightly focused, circ...This paper presents a novel view of the impact of electron collision off-axis positions on the dynamic properties and relativistic nonlinear Thomson inverse scattering of excited electrons within tightly focused, circularly polarized laser pulses of varying intensities. We examine the effects of the transverse ponderomotive force, specifically how the deviation angle and speed of electron motion are affected by the initial off-axis position of the electron and the peak amplitude of the laser pulse. When the laser pulse intensity is low, an increase in the electron's initial off-axis distance results in reduced spatial radiation power, improved collimation, super-continuum phenomena generation, red-shifting of the spectrum's harmonic peak, and significant symmetry in the radiation radial direction. However, in contradiction to conventional understandings,when the laser pulse intensity is relatively high, the properties of the relativistic nonlinear Thomson inverse scattering of the electron deviate from the central axis, changing direction in opposition to the aforementioned effects. After reaching a peak, these properties then shift again, aligning with the previous direction. The complex interplay of these effects suggests a greater nuance and intricacy in the relationship between laser pulse intensity, electron position, and scattering properties than previously thought.展开更多
The nonlinear radiation of the electron is a distinctive feature of the action of tightly focused linearly polarized lasers.In this paper,from the perspective of radiation symmetry,the effect of laser parameters on th...The nonlinear radiation of the electron is a distinctive feature of the action of tightly focused linearly polarized lasers.In this paper,from the perspective of radiation symmetry,the effect of laser parameters on the electron radiation power in the time domain is studied systematically.An asymmetric bimodal structure is found in the time domain in the direction of the maximum radiation.For this special structure,an explanation is given based on the electron dynamics perspective.The structure is compared with the symmetric bimodal structure in the classical theory.The increase in laser intensity,while significantly increasing the radiated power of the electron,exacerbates the asymmetry of the electron radiation.The variation in the initial phase of the laser leads to a periodic variation in the electron motion,which results in a periodic extension of the electron spatial radiation with a period ofπ.Moreover,the existence of jump points with a phase difference ofπin the range of 0-2πis found.The increase in pulse width reduces the radiated power,extends the radiation range,and alleviates the radiation asymmetry.The results in this paper contribute to the study of electron radiation characteristics in intense laser fields.展开更多
By using a high-intensity flying focus laser,the dephasingless[Phys.Rev.Lett.124134802(2020)]or phase-locked[Nat.Photon.14475(2020)]laser wakefield acceleration(LWFA)can be realized,which may overcome issues of laser ...By using a high-intensity flying focus laser,the dephasingless[Phys.Rev.Lett.124134802(2020)]or phase-locked[Nat.Photon.14475(2020)]laser wakefield acceleration(LWFA)can be realized,which may overcome issues of laser diffraction,pump depletion,and electron dephasing which are always suffered in usual LWFA.The scheme thus has the potentiality to accelerate electrons to Te V energy in a single acceleration stage.However,the controlled electron injection has not been self-consistently included in such schemes.Only external injection was suggested in previous theoretical studies,which requires other accelerators and is relatively difficulty to operate.Here,we numerically study the actively controlled density transition injection in phase-locked LWFA to get appropriate density profiles for amount of electron injection.The study shows that compared with LWFA driven by lasers with fixed focus,a larger plasma density gradient is necessary.Electrons experience both transverse and longitudinal loss during acceleration due to the superluminal group velocity of the driver and the variation of the wakefield structure.Furthermore,the periodic deformation and fracture of the flying focus laser in the high-density plasma plateau make the final injected charge also depend on the beginning position of the density downramp.Our studies show a possible way for amount of electron injection in LWFA driven by flying focus lasers.展开更多
This paper presents the experimental progress of laser-focused Cr atomic deposition and the experimental condition. The result is an accurate array of lines with a periodicity of 212.8±0.2 nm and mean full-width ...This paper presents the experimental progress of laser-focused Cr atomic deposition and the experimental condition. The result is an accurate array of lines with a periodicity of 212.8±0.2 nm and mean full-width at half maximum as approximately 95 nm. Surface growth in laser-focused Cr atomic deposition is modeled and studied by kinetic Monte Carlo simulation including two events: the one is that atom trajectories in laser standing wave are simulated with the semiclassical equations of motion to obtain the deposition position; the other is that adatom diffuses by considering two major diffusion processes, namely, terrace diffusion and step-edge descending. Comparing with experimental results (Anderson W R, Bradley C C, McClelland J J and Celotta R J 1999 Phys. Rev. A 59 2476), it finds that the simulated trend of dependence on feature width is in agreement with the power of standing wave, the other two simulated trends are the same in the initial stage. These results demonstrate that some surface diffusion processes play important role in feature width broadening. Numerical result also shows that high incoming beam flux of atoms deposited redounds to decrease the distance between adatoms which can diffuse to minimize the feature width and enhance the contrast.展开更多
In most collisional schemes of x-ray laser (XRL) experiments, a bow-like intensity distribution of XRL is often observed, and it is generally ascribed to the two-dimensional hydrodynamic behaviour of expanding plasm...In most collisional schemes of x-ray laser (XRL) experiments, a bow-like intensity distribution of XRL is often observed, and it is generally ascribed to the two-dimensional hydrodynamic behaviour of expanding plasma. In order to better understand its essence in physics, a newly developed two-dimensional non-equilibrium radiation hydrodynamic code XRL2D is used to simulate a quasi-steady state Ni-like Ag XRL experiment on ShenGuang-Ⅱfacility. The simulation results show that the bow-like distribution of Ni-like ions caused by over-ionization in the central area of plasma is responsible for the bow-like shape of the XRL intensity distribution observed.展开更多
Based on the two-dimensional model, this paper compares the hydrodynamics of slab x-ray laser plasma produced by different nonuniform line focused irradiations. It finds that the average intensity and the duration of ...Based on the two-dimensional model, this paper compares the hydrodynamics of slab x-ray laser plasma produced by different nonuniform line focused irradiations. It finds that the average intensity and the duration of laser pulse and the overall shape of the intensity distribution in the focal line have different influences on the plasma. Calculations show that the evolution of temperature variation is more sensitive to the pulse duration and the electron density variation is more sensitive to the pulse intensity. Pulses with duration of 200 ps to 500 ps and with intensity of 0.2 TW/cm2 to 1.0 TW/cm2 are proved acceptable in slab x-ray lasers.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
We investigate atomic above-threshold ionization in elliptically polarized strong laser fields with a semiclassical approach.With increasing laser intensity,the Coulomb focusing(CF) effects are found to become stron...We investigate atomic above-threshold ionization in elliptically polarized strong laser fields with a semiclassical approach.With increasing laser intensity,the Coulomb focusing(CF) effects are found to become stronger in both parallel and perpendicular directions with respect to the polarization plane.The dependence of CF effects on tunnel exit,initial transverse momentum distribution and laser electric field is analyzed.It was revealed that the effects of tunnel exit are most prominent with variation of the laser intensity,and the other two factors both play non-negligible roles.Our results provide a deeper insight to the recent experiments of Coulomb asymmetry[Shafir D,et al.,2013 Phys.Rev.Lett.111 023005 and Li M,et al,2013 Phys.Rev.Lett.111 023006].展开更多
Water breakdown studies by Nd-YAG laser pulses of duration 100 fs, 30 ps and 6 ns at wavelength 1064 nm are pre- formed to investigate the physical mechanisms which couple the laser energy into the medium. Calculation...Water breakdown studies by Nd-YAG laser pulses of duration 100 fs, 30 ps and 6 ns at wavelength 1064 nm are pre- formed to investigate the physical mechanisms which couple the laser energy into the medium. Calculations are carried out applying a modified kinetic model of water breakdown previously developed by Kennedy (1995) to investigate the correlation between threshold intensity of breakdown and laser pulse length. The modifications considered the introduction of diffusion and recombination loss processes which might take place under the experimental conditions applied in these calculations. The validity of the model is tested by comparing the calculated threshold intensities and the experimentally measured ones where good agreement is shown. The study of the time evolution of the electron density clarifies the correlation between the pulse length and dominant ionization mechanism. The analysis of the spatial distribution of the electron density along the radial and axial distances of the focal spot showed that the size of the formed plasma increases with the increase of the pulse length. On the other hand, studies of self-focusing effect illustrated that under the investigated experimental conditions the effect of this process has an effective contribution only at laser pulses of the order of femtosecond scale when the laser beam is focused by a lens of a focal length ≥8.0 cm. This result in turns assures that using femtosecond pulses in ophthalmic microsurgery could be a safe tool from the retinal damage.展开更多
The focusing of a radially polarized beam without annular apodization ora phase filter at the entrance pupil of the objective results in a wide focus and low purity of the longitudinally polarized component. However, ...The focusing of a radially polarized beam without annular apodization ora phase filter at the entrance pupil of the objective results in a wide focus and low purity of the longitudinally polarized component. However, the presence of a physical annular apodization or phase filter makes some applications more difficult or even impossible. We propose a radially polarized and amplitude-modulated annular multi-Gaussian beam mode. Numerical simulation shows that it can be focused into a sharper focal spot of 0.125λ2 without additional apodizations or filters. The beam quality describing the purity of longitudinally polarized component is up to 86%.展开更多
The bandwidth and the duration of incident pulsed beam are proved to play important roles in modifying the nonlinear image of amplitude-type scatterer. It is found that the initially positive chirp-type bandwidth can ...The bandwidth and the duration of incident pulsed beam are proved to play important roles in modifying the nonlinear image of amplitude-type scatterer. It is found that the initially positive chirp-type bandwidth can suppress the nonlinear image, while the negative one can enhance it, and that both effects are inversely proportional to the incident pulse duration. Numerical simulations further demonstrate that the location of nonlinear image is at the conjugate plane of the scatterer and that, for negatively pre-chirped pulsed beam, the nonlinear image peak intensity can be higher than that in the corresponding monochromatic case under certain conditions. Moreover the effect of group velocity dispersion on nonlinear image is found to be similar to that of chirp-type bandwidth.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos.91950102,12274230,and 11834004)the Funding of Nanjing University of Science and Technology (Grant No.TSXK2022D005)。
文摘Synthesis of multi-color laser pulses has been developed as a promising way to improve low conversion efficiency of high-order harmonic generation(HHG). Here we systematically study the effect of laser focus in a two-color waveform on generation of macroscopic HHG in soft x-rays. We find that the dependence of HHG yields on laser focus at low or high gas pressure is sensitive to the characteristics of single-atom harmonic response, in which “short”-or “long”-trajectory emissions can be selectively controlled by changing the waveform of two-color synthesized laser pulse. We uncover the phase-matching mechanism of HHG in the gas medium by examining the propagation of the two-color waveform and the evolution of time-frequency emissions of high-harmonic field. We further reveal that the nonlinear effects, such as geometric phase, atomic dispersion, and plasma defocusing, are responsible for modification of two-color waveform upon propagation. This work can be used to find better macroscopic conditions for generating soft x-ray HHG by employing two-color optimized waveforms.
基金financially supported by the Provincial Key Research and Development Program of Shandong,China(No.2019GHZ010)the Natural Science Foundation of Shandong Province(No.ZR2020MF123)+1 种基金National Natural Science Foundation of China(Nos.61975190 and12174359)the Fundamental Research Funds for the Central Universities(No.202161002)。
文摘Laser-induced breakdown spectroscopy(LIBS)is a capable technique for elementary analysis,while LIBS quantitation is still under development.In quantitation,precise laser focusing plays an important role because it ensures the distance between the laser and samples.In the present work,we employed spectral intensity as a direct way to assist laser focusing in LIBS quantitation for copper alloys.It is found that both the air emission and the copper line could be used to determine the position of the sample surface by referencing the intensity maximum.Nevertheless,the fine quantitation was only realized at the position where the air emission(e.g.O(I)777.4 nm)reached intensity maximum,and also in this way,a repeatable quantitation was successfully achieved even after 120 days.The results suggested that the LIBS quantitation was highly dependent on the focusing position of the laser,and spectra-assisted focusing could be a simple way to find the identical condition for different samples’detection.In the future,this method might be applicable in field measurements for LIBS analysis of solids.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFA0200902)Science and Technology Commission of Shanghai Municipality,China(Grant No.17JC1400801)Young Scientists Fund of the National Natural Science Foundation of China(Grant No.51705369).
文摘Laser focused atomic deposition is a unique and effective way to fabricate highly accurate pitch standards in nanometrology.However,the stability and repeatability of the atom lithography fabrication process remains a challenging problem for massive production.Based on the atom-light interaction theory,channeling is utilized to improve the stability and repeatability.From the comparison of three kinds of atom-light interaction models,the optimal parameters for channeling are obtained based on simulation.According to the experimental observations,the peak to valley height of Cr nano-gratings keeps stable when the cutting proportion changes from 15%to 50%,which means that the channeling shows up under this condition.The channeling proves to be an effective method to optimize the stability and repeatability of laser focused Cr atomic deposition.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.10947170/A05 and 11104291)the Natural Science Fund for Colleges and Universities in Jiangsu Province (Grant No.10KJB140006)+2 种基金the Natural Sciences Foundation of Shanghai (Grant No.11ZR1441300)the Natural Science Foundation of Nanjing University of Posts and Telecommunications (Grant No.NY221098)the Jiangsu Qing Lan Project for their sponsorship。
文摘This paper presents a novel view of the impact of electron collision off-axis positions on the dynamic properties and relativistic nonlinear Thomson inverse scattering of excited electrons within tightly focused, circularly polarized laser pulses of varying intensities. We examine the effects of the transverse ponderomotive force, specifically how the deviation angle and speed of electron motion are affected by the initial off-axis position of the electron and the peak amplitude of the laser pulse. When the laser pulse intensity is low, an increase in the electron's initial off-axis distance results in reduced spatial radiation power, improved collimation, super-continuum phenomena generation, red-shifting of the spectrum's harmonic peak, and significant symmetry in the radiation radial direction. However, in contradiction to conventional understandings,when the laser pulse intensity is relatively high, the properties of the relativistic nonlinear Thomson inverse scattering of the electron deviate from the central axis, changing direction in opposition to the aforementioned effects. After reaching a peak, these properties then shift again, aligning with the previous direction. The complex interplay of these effects suggests a greater nuance and intricacy in the relationship between laser pulse intensity, electron position, and scattering properties than previously thought.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.10947170/A05 and 11104291)Natural Science Fund for Colleges and Universities in Jiangsu Province (Grant No.10KJB140006)+2 种基金Natural Science Foundation of Shanghai (Grant No.11ZR1441300)Natural Science Foundation of Nanjing University of Posts and Telecommunications (Grant No.NY221098)sponsored by the Jiangsu Qing Lan Project and STITP Project (Grant No.CXXYB2022516)。
文摘The nonlinear radiation of the electron is a distinctive feature of the action of tightly focused linearly polarized lasers.In this paper,from the perspective of radiation symmetry,the effect of laser parameters on the electron radiation power in the time domain is studied systematically.An asymmetric bimodal structure is found in the time domain in the direction of the maximum radiation.For this special structure,an explanation is given based on the electron dynamics perspective.The structure is compared with the symmetric bimodal structure in the classical theory.The increase in laser intensity,while significantly increasing the radiated power of the electron,exacerbates the asymmetry of the electron radiation.The variation in the initial phase of the laser leads to a periodic variation in the electron motion,which results in a periodic extension of the electron spatial radiation with a period ofπ.Moreover,the existence of jump points with a phase difference ofπin the range of 0-2πis found.The increase in pulse width reduces the radiated power,extends the radiation range,and alleviates the radiation asymmetry.The results in this paper contribute to the study of electron radiation characteristics in intense laser fields.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11991074,12225505 and12135009)。
文摘By using a high-intensity flying focus laser,the dephasingless[Phys.Rev.Lett.124134802(2020)]or phase-locked[Nat.Photon.14475(2020)]laser wakefield acceleration(LWFA)can be realized,which may overcome issues of laser diffraction,pump depletion,and electron dephasing which are always suffered in usual LWFA.The scheme thus has the potentiality to accelerate electrons to Te V energy in a single acceleration stage.However,the controlled electron injection has not been self-consistently included in such schemes.Only external injection was suggested in previous theoretical studies,which requires other accelerators and is relatively difficulty to operate.Here,we numerically study the actively controlled density transition injection in phase-locked LWFA to get appropriate density profiles for amount of electron injection.The study shows that compared with LWFA driven by lasers with fixed focus,a larger plasma density gradient is necessary.Electrons experience both transverse and longitudinal loss during acceleration due to the superluminal group velocity of the driver and the variation of the wakefield structure.Furthermore,the periodic deformation and fracture of the flying focus laser in the high-density plasma plateau make the final injected charge also depend on the beginning position of the density downramp.Our studies show a possible way for amount of electron injection in LWFA driven by flying focus lasers.
基金Project supported by the Nanoscience Foundation of Shanghai,China (Grant Nos. 0852nm07000 and 0952nm07000)the National Natural Science Foundation of China (Grant No. 10804084)the National Science & Technology Support Project (Grant No. 2006BAF06B08)
文摘This paper presents the experimental progress of laser-focused Cr atomic deposition and the experimental condition. The result is an accurate array of lines with a periodicity of 212.8±0.2 nm and mean full-width at half maximum as approximately 95 nm. Surface growth in laser-focused Cr atomic deposition is modeled and studied by kinetic Monte Carlo simulation including two events: the one is that atom trajectories in laser standing wave are simulated with the semiclassical equations of motion to obtain the deposition position; the other is that adatom diffuses by considering two major diffusion processes, namely, terrace diffusion and step-edge descending. Comparing with experimental results (Anderson W R, Bradley C C, McClelland J J and Celotta R J 1999 Phys. Rev. A 59 2476), it finds that the simulated trend of dependence on feature width is in agreement with the power of standing wave, the other two simulated trends are the same in the initial stage. These results demonstrate that some surface diffusion processes play important role in feature width broadening. Numerical result also shows that high incoming beam flux of atoms deposited redounds to decrease the distance between adatoms which can diffuse to minimize the feature width and enhance the contrast.
文摘In most collisional schemes of x-ray laser (XRL) experiments, a bow-like intensity distribution of XRL is often observed, and it is generally ascribed to the two-dimensional hydrodynamic behaviour of expanding plasma. In order to better understand its essence in physics, a newly developed two-dimensional non-equilibrium radiation hydrodynamic code XRL2D is used to simulate a quasi-steady state Ni-like Ag XRL experiment on ShenGuang-Ⅱfacility. The simulation results show that the bow-like distribution of Ni-like ions caused by over-ionization in the central area of plasma is responsible for the bow-like shape of the XRL intensity distribution observed.
基金suported by the National Natural Science Foundation of China (Grant No. 10874242)the National Basic Research Program of China (973 Program) (Grant No. 2007CB815105)Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20070290008)
文摘Based on the two-dimensional model, this paper compares the hydrodynamics of slab x-ray laser plasma produced by different nonuniform line focused irradiations. It finds that the average intensity and the duration of laser pulse and the overall shape of the intensity distribution in the focal line have different influences on the plasma. Calculations show that the evolution of temperature variation is more sensitive to the pulse duration and the electron density variation is more sensitive to the pulse intensity. Pulses with duration of 200 ps to 500 ps and with intensity of 0.2 TW/cm2 to 1.0 TW/cm2 are proved acceptable in slab x-ray lasers.
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Project supported by the National Natural Science Foundation of China(Grant Nos.11547218,11564020,and 11504314)
文摘We investigate atomic above-threshold ionization in elliptically polarized strong laser fields with a semiclassical approach.With increasing laser intensity,the Coulomb focusing(CF) effects are found to become stronger in both parallel and perpendicular directions with respect to the polarization plane.The dependence of CF effects on tunnel exit,initial transverse momentum distribution and laser electric field is analyzed.It was revealed that the effects of tunnel exit are most prominent with variation of the laser intensity,and the other two factors both play non-negligible roles.Our results provide a deeper insight to the recent experiments of Coulomb asymmetry[Shafir D,et al.,2013 Phys.Rev.Lett.111 023005 and Li M,et al,2013 Phys.Rev.Lett.111 023006].
文摘Water breakdown studies by Nd-YAG laser pulses of duration 100 fs, 30 ps and 6 ns at wavelength 1064 nm are pre- formed to investigate the physical mechanisms which couple the laser energy into the medium. Calculations are carried out applying a modified kinetic model of water breakdown previously developed by Kennedy (1995) to investigate the correlation between threshold intensity of breakdown and laser pulse length. The modifications considered the introduction of diffusion and recombination loss processes which might take place under the experimental conditions applied in these calculations. The validity of the model is tested by comparing the calculated threshold intensities and the experimentally measured ones where good agreement is shown. The study of the time evolution of the electron density clarifies the correlation between the pulse length and dominant ionization mechanism. The analysis of the spatial distribution of the electron density along the radial and axial distances of the focal spot showed that the size of the formed plasma increases with the increase of the pulse length. On the other hand, studies of self-focusing effect illustrated that under the investigated experimental conditions the effect of this process has an effective contribution only at laser pulses of the order of femtosecond scale when the laser beam is focused by a lens of a focal length ≥8.0 cm. This result in turns assures that using femtosecond pulses in ophthalmic microsurgery could be a safe tool from the retinal damage.
基金supported by the National Natural Science Foundation of China(Grant No.11074105)the Natural Science Foundation of Shandong Province,China(Grant No.ZR2010AM038)+1 种基金the Precision Instruments Upgrade Transforming Fund of Shandong Province,China(Grant No.2010GJC20808-16)the Research Fund of Education Department of Shandong Province,China (Grant No.J11LA11)
文摘The focusing of a radially polarized beam without annular apodization ora phase filter at the entrance pupil of the objective results in a wide focus and low purity of the longitudinally polarized component. However, the presence of a physical annular apodization or phase filter makes some applications more difficult or even impossible. We propose a radially polarized and amplitude-modulated annular multi-Gaussian beam mode. Numerical simulation shows that it can be focused into a sharper focal spot of 0.125λ2 without additional apodizations or filters. The beam quality describing the purity of longitudinally polarized component is up to 86%.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60890202 and 10974049)
文摘The bandwidth and the duration of incident pulsed beam are proved to play important roles in modifying the nonlinear image of amplitude-type scatterer. It is found that the initially positive chirp-type bandwidth can suppress the nonlinear image, while the negative one can enhance it, and that both effects are inversely proportional to the incident pulse duration. Numerical simulations further demonstrate that the location of nonlinear image is at the conjugate plane of the scatterer and that, for negatively pre-chirped pulsed beam, the nonlinear image peak intensity can be higher than that in the corresponding monochromatic case under certain conditions. Moreover the effect of group velocity dispersion on nonlinear image is found to be similar to that of chirp-type bandwidth.