The electron injection and acceleration driven by a few-cycle laser with a sharp vacuum-plasma boundary have been investigated through three-dimensional(3D)particle-in-cell simulations.It is found that an isotropic bo...The electron injection and acceleration driven by a few-cycle laser with a sharp vacuum-plasma boundary have been investigated through three-dimensional(3D)particle-in-cell simulations.It is found that an isotropic boundary impact injection(BII)first occurs at the vacuum-plasma boundary,and then carrier-envelope-phase(CEP)shift causes the transverse oscillation of the plasma bubble,resulting in a periodic electron self-injection(SI)in the laser polarization direction.It shows that the electron charge of the BII only accounts for a small part of the total charge,and the CEP can effectively tune the quality of the injected electron beam.The dependences of laser intensity and electron density on the total charge and the ratio of BII charge to the total charge are studied.The results are beneficial to electron acceleration and its applications,such as betatron radiation source.展开更多
We theoretically investigate the characteristics of terahertz(THz) radiation from monolayer graphene exposed to normal incident few-cycle laser pulses, by numerically solving the extended semiconductor Bloch equations...We theoretically investigate the characteristics of terahertz(THz) radiation from monolayer graphene exposed to normal incident few-cycle laser pulses, by numerically solving the extended semiconductor Bloch equations. Our simulations show that the THz spectra in low frequency regions are highly dependent on the carrier envelope phase(CEP) of driving laser pulses. Using an optimal CEP of few-cycle laser pulses, we can obtain broadband strong THz waves, due to the symmetry breaking of the laser-graphene system. Our results also show that the strength of the THz spectra depend on both the intensity and central wavelength of the laser pulses. The intensity dependence of the THz wave can be described by the excitation rate of graphene, while wavelength dependence can be traced back to the band velocity and the population of graphene. We find that a near single-cycle THz pulse can be obtained from graphene driven by a mid-infrared laser pulse.展开更多
The field-free alignment of molecule Cl CN is investigated by using a terahertz few-cycle pulse(THz FCP)based on the time-dependent density matrix theory.It is shown that a high degree of molecular alignment can be ob...The field-free alignment of molecule Cl CN is investigated by using a terahertz few-cycle pulse(THz FCP)based on the time-dependent density matrix theory.It is shown that a high degree of molecular alignment can be obtained by changing the matching number of the THz FCPs in the adiabatic regime and the non-adiabatic regime.The matching number can affect both the maximum value of the alignment and the time at which it is achieved.It is also found that a higher degree of alignment can be achieved by using the THz FCP at lower intensity and there exists an optimal threshold of molecular alignment with the increase of the field amplitude.Also found is the frequency sensitive region in which the degree of maximum alignment can be enhanced greatly by modulating the center frequencies of different THz FCPs.The investigation demonstrates that comparing with a THz single-cycle pulse,a better result of the field-free alignment can be created by a THz FCP at a constant rotational temperature of molecule.展开更多
An all-reflective self-referenced spectral interferometry based on the transient grating(TG)effect is proposed for single-shot measuring of the amplitude and phase of ultrashort pulses in a broadband spectral range.Ex...An all-reflective self-referenced spectral interferometry based on the transient grating(TG)effect is proposed for single-shot measuring of the amplitude and phase of ultrashort pulses in a broadband spectral range.Except for a thin third-order nonlinear medium,which was used to generate the TG signal,no transmitted optics were used in the proposed device,and few-cycle pulses in a broad spectral range from deep UV to mid-IR can be characterized.With a homemade compact and alignment-free device,a 5.0 fs pulse at 800 nm corresponding to about two cycles and a 14.3 fs pulse at 1800 nm corresponding to less than three cycles were successfully characterized.展开更多
We theoretically study the coherent transport of a single electron between the ground states of a double coupled quantum dot structure. The coherent transport is externally controlled by applying a few-cycle pulse wit...We theoretically study the coherent transport of a single electron between the ground states of a double coupled quantum dot structure. The coherent transport is externally controlled by applying a few-cycle pulse with an adjustable carrier-envelope phase(CEP). By simulating numerically, it is shown that there exhibits a strong dependence of electron transport on the CEP and on the arrival time of few-cycle pulse. We provide a simple analytical description for this phenomenon by approximating the quantum dot structure as a three-level Λ-type system. These results also illustrate the potential of utilizing excitation in coupled quantum dots as a means of measuring the CEP of few-cycle pulses.展开更多
High-power femtosecond lasers beyond 5μm are attractive for strong-field physics with mid-infrared(IR)fields but are difficult to scale up.In optical parametric chirped-pulse amplification(OPCPA)at mid-IR wavelengths...High-power femtosecond lasers beyond 5μm are attractive for strong-field physics with mid-infrared(IR)fields but are difficult to scale up.In optical parametric chirped-pulse amplification(OPCPA)at mid-IR wavelengths,a nonlinear crystal is vital,and its transmittance,dispersion,nonlinear coefficient and size determine the achievable power and wavelength.OPCPA beyond 5μm routinely relies on semiconductor crystals because common oxide crystals are not transparent in this spectral range.However,the small size and low damage threshold of semiconductor crystals fundamentally limit the peak power to gigawatts.In this paper,we design a terawatt-class OPCPA system at 5.2μm based on a new kind of oxide crystal of La3Ga5.5Nb0.5O14(LGN).The extended transparent range,high damage threshold,superior phase-matching characteristics and large size of LGN enable the generation of 0.13 TW seven-cycle pulses at5.2μm.This design fully relies on the state-of-the-art OPCPA technology of an octave-spanning ultrafast Ti:sapphire laser and a thin-disk Yb:YAG laser,offering the performance characteristics of high power,a high repetition rate and a stable carrier-envelope phase.展开更多
The high harmonic generation(HHG)by few-cycle laser pulses is essential for research in strong-field solid-state physics.Through comparison of high harmonic spectra of solids generated by laser pulses with varying dur...The high harmonic generation(HHG)by few-cycle laser pulses is essential for research in strong-field solid-state physics.Through comparison of high harmonic spectra of solids generated by laser pulses with varying durations,we discovered that lasers with good dispersion compensation are capable of producing a broad spectrum of high harmonics.As the pulse duration is further compressed,several interference peaks appear in the broad spectrum.Moreover,we conducted simulations using the semiconductor Bloch equation,considering the effect of Berry curvature,to better understand this process.Our work provides a valuable approach for studying HHG by few-cycle laser pulses in solid materials,expanding the application of HHG in attosecond physics.展开更多
We propose a spatially chirped quasi-phase-matching(QPM)scheme that enables ultrabroadband second-harmonic-generation(SHG)by using a fan-out QPM grating to frequency-convert a spatially chirped fundamental wave.A“zer...We propose a spatially chirped quasi-phase-matching(QPM)scheme that enables ultrabroadband second-harmonic-generation(SHG)by using a fan-out QPM grating to frequency-convert a spatially chirped fundamental wave.A“zerodispersion”4f system maps the spectral contents of ultrabroadband fundamental onto different spatial coordinates in the Fourier plane,where the fundamental is quasi-monochromatic locally in picosecond duration,fundamentally canceling high-order phase mismatch.A fan-out QPM grating characterized by a linear variation of the poling period along the transverse direction exactly supports the QPM of the spatially chirped beam.We theoretically demonstrate the SHG of an 810-nm,12.1-fs pulse into a 405-nm,10.2-fs pulse with a conversion efficiency of 77%.展开更多
We demonstrate an ultra-broadband high temporal contrast infrared laser source based on cascaded optical parametric amplification,hollow-core fiber(HCF)and second harmonic generation processes.In this setup,the spectr...We demonstrate an ultra-broadband high temporal contrast infrared laser source based on cascaded optical parametric amplification,hollow-core fiber(HCF)and second harmonic generation processes.In this setup,the spectrum of an approximately 1.8μm laser pulse has near 1μm full bandwidth by employing an argon gas-filled HCF.Subsequently,after frequency doubling with cascaded crystals and dispersion compensation by a fused silica wedge pair,9.6 fs(~3cycles)and 150μJ pulses centered at 910 nm with full bandwidth of over 300 nm can be generated.The energy stability of the output laser pulse is excellent with 0.8%(root mean square)over 20 min,and the temporal contrast is>10^(12)at-10 ps before the main pulse.The excellent temporal and spatial characteristics and stability make this laser able to be used as a good seed source for ultra-intense and ultrafast laser systems.展开更多
基金the National Natural Science Foundation of China(Grant Nos.12005297,12175309,12175310,11975308,and 12275356)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA25050200)+3 种基金the Research Project of NUDT(Grant No.ZK21-12)the Key Laboratory Foundation of Laser Plasma of Ministry of Educationthe financial support from the NUDT Young Innovator Awards(Grant No.20190102)Outstanding Young Talents。
文摘The electron injection and acceleration driven by a few-cycle laser with a sharp vacuum-plasma boundary have been investigated through three-dimensional(3D)particle-in-cell simulations.It is found that an isotropic boundary impact injection(BII)first occurs at the vacuum-plasma boundary,and then carrier-envelope-phase(CEP)shift causes the transverse oscillation of the plasma bubble,resulting in a periodic electron self-injection(SI)in the laser polarization direction.It shows that the electron charge of the BII only accounts for a small part of the total charge,and the CEP can effectively tune the quality of the injected electron beam.The dependences of laser intensity and electron density on the total charge and the ratio of BII charge to the total charge are studied.The results are beneficial to electron acceleration and its applications,such as betatron radiation source.
基金Supported by the National Natural Science Foundation of China (Grant Nos.11764038,11864037,11765018,and 91850209)。
文摘We theoretically investigate the characteristics of terahertz(THz) radiation from monolayer graphene exposed to normal incident few-cycle laser pulses, by numerically solving the extended semiconductor Bloch equations. Our simulations show that the THz spectra in low frequency regions are highly dependent on the carrier envelope phase(CEP) of driving laser pulses. Using an optimal CEP of few-cycle laser pulses, we can obtain broadband strong THz waves, due to the symmetry breaking of the laser-graphene system. Our results also show that the strength of the THz spectra depend on both the intensity and central wavelength of the laser pulses. The intensity dependence of the THz wave can be described by the excitation rate of graphene, while wavelength dependence can be traced back to the band velocity and the population of graphene. We find that a near single-cycle THz pulse can be obtained from graphene driven by a mid-infrared laser pulse.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12274265 and 11874241)the Taishan Scholar Project of Shandong Province,China。
文摘The field-free alignment of molecule Cl CN is investigated by using a terahertz few-cycle pulse(THz FCP)based on the time-dependent density matrix theory.It is shown that a high degree of molecular alignment can be obtained by changing the matching number of the THz FCPs in the adiabatic regime and the non-adiabatic regime.The matching number can affect both the maximum value of the alignment and the time at which it is achieved.It is also found that a higher degree of alignment can be achieved by using the THz FCP at lower intensity and there exists an optimal threshold of molecular alignment with the increase of the field amplitude.Also found is the frequency sensitive region in which the degree of maximum alignment can be enhanced greatly by modulating the center frequencies of different THz FCPs.The investigation demonstrates that comparing with a THz single-cycle pulse,a better result of the field-free alignment can be created by a THz FCP at a constant rotational temperature of molecule.
基金supported by the Natural Science Foundation of Shanghai(No.18ZR1413600)the National Natural Science Foundation of China(NSFC)(Nos.61521093 and 61527821)+2 种基金the Instrument Developing Project of the Chinese Academy of Sciences(No.YZ201538)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB160106)the Shanghai Municipal Science and Technology Major Project(No.2017SHZDZX02).
文摘An all-reflective self-referenced spectral interferometry based on the transient grating(TG)effect is proposed for single-shot measuring of the amplitude and phase of ultrashort pulses in a broadband spectral range.Except for a thin third-order nonlinear medium,which was used to generate the TG signal,no transmitted optics were used in the proposed device,and few-cycle pulses in a broad spectral range from deep UV to mid-IR can be characterized.With a homemade compact and alignment-free device,a 5.0 fs pulse at 800 nm corresponding to about two cycles and a 14.3 fs pulse at 1800 nm corresponding to less than three cycles were successfully characterized.
基金Supported in part by National Natural Science Foundation of China under Grant Nos.11374050 and 61372102Qing Lan Project of Jiangsu,and the Fundamental Research Funds for the Central Universities under Grant No.2242012R30011
文摘We theoretically study the coherent transport of a single electron between the ground states of a double coupled quantum dot structure. The coherent transport is externally controlled by applying a few-cycle pulse with an adjustable carrier-envelope phase(CEP). By simulating numerically, it is shown that there exhibits a strong dependence of electron transport on the CEP and on the arrival time of few-cycle pulse. We provide a simple analytical description for this phenomenon by approximating the quantum dot structure as a three-level Λ-type system. These results also illustrate the potential of utilizing excitation in coupled quantum dots as a means of measuring the CEP of few-cycle pulses.
基金supported in part by the National Natural Science Foundation of China(Nos.6170512861727820 and 91850203)Science and Technology Commission of Shanghai Municipality(Nos.17YF1409100 and17ZR1414000)。
文摘High-power femtosecond lasers beyond 5μm are attractive for strong-field physics with mid-infrared(IR)fields but are difficult to scale up.In optical parametric chirped-pulse amplification(OPCPA)at mid-IR wavelengths,a nonlinear crystal is vital,and its transmittance,dispersion,nonlinear coefficient and size determine the achievable power and wavelength.OPCPA beyond 5μm routinely relies on semiconductor crystals because common oxide crystals are not transparent in this spectral range.However,the small size and low damage threshold of semiconductor crystals fundamentally limit the peak power to gigawatts.In this paper,we design a terawatt-class OPCPA system at 5.2μm based on a new kind of oxide crystal of La3Ga5.5Nb0.5O14(LGN).The extended transparent range,high damage threshold,superior phase-matching characteristics and large size of LGN enable the generation of 0.13 TW seven-cycle pulses at5.2μm.This design fully relies on the state-of-the-art OPCPA technology of an octave-spanning ultrafast Ti:sapphire laser and a thin-disk Yb:YAG laser,offering the performance characteristics of high power,a high repetition rate and a stable carrier-envelope phase.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.91850209 and 11974416)。
文摘The high harmonic generation(HHG)by few-cycle laser pulses is essential for research in strong-field solid-state physics.Through comparison of high harmonic spectra of solids generated by laser pulses with varying durations,we discovered that lasers with good dispersion compensation are capable of producing a broad spectrum of high harmonics.As the pulse duration is further compressed,several interference peaks appear in the broad spectrum.Moreover,we conducted simulations using the semiconductor Bloch equation,considering the effect of Berry curvature,to better understand this process.Our work provides a valuable approach for studying HHG by few-cycle laser pulses in solid materials,expanding the application of HHG in attosecond physics.
基金supported by the National Natural Science Foundation of China(Nos.62122049 and 62375165)the Shanghai Rising-Star Program(No.21QA1404600)。
文摘We propose a spatially chirped quasi-phase-matching(QPM)scheme that enables ultrabroadband second-harmonic-generation(SHG)by using a fan-out QPM grating to frequency-convert a spatially chirped fundamental wave.A“zerodispersion”4f system maps the spectral contents of ultrabroadband fundamental onto different spatial coordinates in the Fourier plane,where the fundamental is quasi-monochromatic locally in picosecond duration,fundamentally canceling high-order phase mismatch.A fan-out QPM grating characterized by a linear variation of the poling period along the transverse direction exactly supports the QPM of the spatially chirped beam.We theoretically demonstrate the SHG of an 810-nm,12.1-fs pulse into a 405-nm,10.2-fs pulse with a conversion efficiency of 77%.
基金supported by the National Key R&D Program of China(2017YFE0123700)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB1603)+3 种基金the National Natural Science Foundation of China(61925507,62075227,12004402,61635012)the Program of Shanghai Academic/Technology Research Leader(18XD1404200)the Shanghai Municipal Science and Technology Major Project(2017SHZDZX02)the Youth Innovation Promotion Association CAS(2020248)
文摘We demonstrate an ultra-broadband high temporal contrast infrared laser source based on cascaded optical parametric amplification,hollow-core fiber(HCF)and second harmonic generation processes.In this setup,the spectrum of an approximately 1.8μm laser pulse has near 1μm full bandwidth by employing an argon gas-filled HCF.Subsequently,after frequency doubling with cascaded crystals and dispersion compensation by a fused silica wedge pair,9.6 fs(~3cycles)and 150μJ pulses centered at 910 nm with full bandwidth of over 300 nm can be generated.The energy stability of the output laser pulse is excellent with 0.8%(root mean square)over 20 min,and the temporal contrast is>10^(12)at-10 ps before the main pulse.The excellent temporal and spatial characteristics and stability make this laser able to be used as a good seed source for ultra-intense and ultrafast laser systems.
