The generation of terahertz (THz) emission from air plasma induced by two-color femtosecond laser pulses is studied on the basis of a transient photocurrent model. While the gas is ionized by the two-color femtoseco...The generation of terahertz (THz) emission from air plasma induced by two-color femtosecond laser pulses is studied on the basis of a transient photocurrent model. While the gas is ionized by the two-color femtosecond laser-pulses com- posed of the fundamental and its second harmonic, a non-vanishing directional photoelectron current emerges, radiating a THz electromagnetic pulse. The gas ionization processes at three different laser-pulse energies are simulated, and the corresponding THz waveforms and spectra are plotted. The results demonstrate that, by keeping the laser-pulse width and the relative phase between two pulses invariant when the laser energy is at a moderate value, the emitted THz fields are significantly enhanced with a near-linear dependence on the optical energy.展开更多
The wave packet dynamics of I2^- anions is studied by using the time-dependent wave packet method. Two conclusions can be drawn from the calculations. First, the period of the total photoelectron signal oscillating wi...The wave packet dynamics of I2^- anions is studied by using the time-dependent wave packet method. Two conclusions can be drawn from the calculations. First, the period of the total photoelectron signal oscillating with the propagation of delay time is about 750fs. Second, the photoionization of I2^- anions begin at the time 600 fs, and the time needed for the population of the electronic state of I2 neutral molecule to reach the maximum becomes shorter with the increasing delay time.展开更多
Damage points induced by 355 nm laser irradiation increase more quickly on the surface of fused silica in vacuum of about 10^-3 Pa than in atmospheric air at the same fluence. The larger concentration of point defects...Damage points induced by 355 nm laser irradiation increase more quickly on the surface of fused silica in vacuum of about 10^-3 Pa than in atmospheric air at the same fluence. The larger concentration of point defects in vacuum is confirmed by photoluminescence intensity. X-ray photoelectron spectroscopy and infrared absorption indicate the formation of sub-stoichiometric silica on the surface. The degradation mechanism of fused silica in vacuum is discussed.展开更多
We report the results of our investigation on the loss property of a birefringent photonic crystal fibre (PCF) based on a particular periodic arrangement of air-holes and pure silica. The structure of the birefringe...We report the results of our investigation on the loss property of a birefringent photonic crystal fibre (PCF) based on a particular periodic arrangement of air-holes and pure silica. The structure of the birefringent PCF, whose air-hole diameter in one ring is always larger than the next inner ring, presents an obviously low confinement loss than the one whose air-hole (except those on the horizontal line) diameter is constant. It is shown from numerical results that a four-ring PCF with birefringenee B=5×10^-4 and fast axis confinement loss of 4.5×10^-3 dB/km at wavelength of 1.55μm can be designed.展开更多
The effect of pulse temporal profiles on the Autler-Townes (AT) splitting in photoelectron spectra is theoretically studied by employing the time-dependent wave packet method for a rotational Na2 molecule. The AT sp...The effect of pulse temporal profiles on the Autler-Townes (AT) splitting in photoelectron spectra is theoretically studied by employing the time-dependent wave packet method for a rotational Na2 molecule. The AT splitting which results from the sufficient Rabi oscillations is affected by the pulse profile and molecular alignment. The AT splitting may be observed only by utilizing proper pulse profiles with a certain intensity.展开更多
An optimal feedback control of two-photon fluorescence in the ethanol solution of 4-dicyanomethylene-2-methyl- 6-p-dimethyl-aminostryryl-4H-pyran (DCM) using pulse-shaping technique based on genetic algorithm is dem...An optimal feedback control of two-photon fluorescence in the ethanol solution of 4-dicyanomethylene-2-methyl- 6-p-dimethyl-aminostryryl-4H-pyran (DCM) using pulse-shaping technique based on genetic algorithm is demon- strated experimentally. The two-photon fluorescence of the DCM ethanol solution is enhanced in intensity of about 23%. The second harmonic generation frequency-resolved optical gating (SHG-FROG) trace indicates that the effective population transfer arises from the positively chirped pulse. The experimental results appear the potential applications of coherent control to the complicated molecular system.展开更多
Selective excitation of coherent anti-Stokes Raman scattering from the benzene solution is achieved by adaptive pulse shaping based on genetic algorithm, and second harmonic generation frequency-resolved optical gati...Selective excitation of coherent anti-Stokes Raman scattering from the benzene solution is achieved by adaptive pulse shaping based on genetic algorithm, and second harmonic generation frequency-resolved optical gating (SHG-FROG) technique is adopted to characterize the original and optimal laser pulses. The mechanism for two-pulse coherent mode-selective excitation of Raman scattering is experimentally investigated by modulating the pump pulse in the frequency domain, and it is indicated that two-pulse coherent mode-selective excitation of Raman scattering mainly depends on the effective frequency components of the pump pulse related to specific vibrational mode. The experimental results suggest that two-pulse CARS has good signal-to-background ratio and high sensitivity, and it has attractive potential applications in the complicated molecular system.展开更多
We have experimentally demonstrated pulses 0.4 mJ in duration smaller than 12 fs with an excellent spatial beam profile by self-guided propagation in argon. The original 52 fs pulses from the chirped pulsed amplificat...We have experimentally demonstrated pulses 0.4 mJ in duration smaller than 12 fs with an excellent spatial beam profile by self-guided propagation in argon. The original 52 fs pulses from the chirped pulsed amplification laser system are first precompressed to 32 fs by inserting an acoustic optical programmable dispersive filter instrument into the laser system for spectrum reshaping and dispersion compensation, and the pulse spectrum is subsequently broadened by filamentation in an argon cell. By using chirped mirrors for post-dispersion compensation, the pulses are successfully compressed to smaller than 12 fs.展开更多
By means of the numerical solution of time-dependent Schr6dinger equation, we verify a scaling law of photoionization in ultrashort pulses. We find that for a given carrier-envelope phase and duration of the pulse, id...By means of the numerical solution of time-dependent Schr6dinger equation, we verify a scaling law of photoionization in ultrashort pulses. We find that for a given carrier-envelope phase and duration of the pulse, identical photoionizations are obtained provided that when the central frequency of the pulse is enlarged by k times, the atomic binding potential is enlarged by k times, and the laser intensity is enlarged by ka times. The scaling law allows us to reach a significant control over direction of photoemission and offers exciting prospects of reaching similar physical processes in different interacting systems which constitutes a novel kind of coherent control.展开更多
A novel technique for high-power extracavity pulse compression with a nonlinear solid material is demonstrated. Before spectral broadening by self-phase modulation in the solid material, a short filament generated in ...A novel technique for high-power extracavity pulse compression with a nonlinear solid material is demonstrated. Before spectral broadening by self-phase modulation in the solid material, a short filament generated in argon is used as a spatial filter, which works for a uniform spectrum broadening over the spatial profile. Compensated by chirped mirrors, a 15-fs pulse is generated from a 32-fs input laser pulse. A total transmission larger than 80% after the solid material is achieved.展开更多
We theoretically investigate the coherent enhancement of resonant two-photon transitions (TPT) in a three-level atomic system. The TPT can be coherently enhanced by modulating spectral amplitude due to eliminating t...We theoretically investigate the coherent enhancement of resonant two-photon transitions (TPT) in a three-level atomic system. The TPT can be coherently enhanced by modulating spectral amplitude due to eliminating the destructive interference, though partial laser energy losses. Maximal enhancement of TPT can be achieved by modulating spectral phase due to establishing completely constructive interference. Our research provides a theoretical basis for experimental investigation and appears to have potential application on coherent control in the complicated quantum system.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No.61177095)the Natural Science Foundation of Hubei Province,China(Grant No.2012FFA074)+1 种基金the Ph.D.Programs Foundation of Ministry of Education of China (Grant No.20100142110042)the Fundamental Research Funds for the Central Universities (Grant Nos.2012QN094 and 2012QN097)
文摘The generation of terahertz (THz) emission from air plasma induced by two-color femtosecond laser pulses is studied on the basis of a transient photocurrent model. While the gas is ionized by the two-color femtosecond laser-pulses com- posed of the fundamental and its second harmonic, a non-vanishing directional photoelectron current emerges, radiating a THz electromagnetic pulse. The gas ionization processes at three different laser-pulse energies are simulated, and the corresponding THz waveforms and spectra are plotted. The results demonstrate that, by keeping the laser-pulse width and the relative phase between two pulses invariant when the laser energy is at a moderate value, the emitted THz fields are significantly enhanced with a near-linear dependence on the optical energy.
基金Supported by the National Natural Science Foundation of China under Grant No 10575017. The code used in our calculation is provided by Professor Ke-Li Han and we appreciate his help and kind advice.
文摘The wave packet dynamics of I2^- anions is studied by using the time-dependent wave packet method. Two conclusions can be drawn from the calculations. First, the period of the total photoelectron signal oscillating with the propagation of delay time is about 750fs. Second, the photoionization of I2^- anions begin at the time 600 fs, and the time needed for the population of the electronic state of I2 neutral molecule to reach the maximum becomes shorter with the increasing delay time.
文摘Damage points induced by 355 nm laser irradiation increase more quickly on the surface of fused silica in vacuum of about 10^-3 Pa than in atmospheric air at the same fluence. The larger concentration of point defects in vacuum is confirmed by photoluminescence intensity. X-ray photoelectron spectroscopy and infrared absorption indicate the formation of sub-stoichiometric silica on the surface. The degradation mechanism of fused silica in vacuum is discussed.
文摘We report the results of our investigation on the loss property of a birefringent photonic crystal fibre (PCF) based on a particular periodic arrangement of air-holes and pure silica. The structure of the birefringent PCF, whose air-hole diameter in one ring is always larger than the next inner ring, presents an obviously low confinement loss than the one whose air-hole (except those on the horizontal line) diameter is constant. It is shown from numerical results that a four-ring PCF with birefringenee B=5×10^-4 and fast axis confinement loss of 4.5×10^-3 dB/km at wavelength of 1.55μm can be designed.
基金Supported by the National Natural Science Foundation of China under Grant No 10374012.
文摘The effect of pulse temporal profiles on the Autler-Townes (AT) splitting in photoelectron spectra is theoretically studied by employing the time-dependent wave packet method for a rotational Na2 molecule. The AT splitting which results from the sufficient Rabi oscillations is affected by the pulse profile and molecular alignment. The AT splitting may be observed only by utilizing proper pulse profiles with a certain intensity.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10234030 and 10374030, the National Key Project for Basic Research of China under Grant No 1999075204, the Programme for New Century Excellent Talents in Universities of China (NCET-04-0420), the Shanghai Science and Technology Committee (No 036105019), and the Twilight Project Sponsored by the Shanghai Education Committee (No 03SG23).
文摘An optimal feedback control of two-photon fluorescence in the ethanol solution of 4-dicyanomethylene-2-methyl- 6-p-dimethyl-aminostryryl-4H-pyran (DCM) using pulse-shaping technique based on genetic algorithm is demon- strated experimentally. The two-photon fluorescence of the DCM ethanol solution is enhanced in intensity of about 23%. The second harmonic generation frequency-resolved optical gating (SHG-FROG) trace indicates that the effective population transfer arises from the positively chirped pulse. The experimental results appear the potential applications of coherent control to the complicated molecular system.
基金Supported by the National Natural Science Foundation of China under Grant No 10574046, the National Basic Research Programme of China under Grant Nos 2006CB806006 and 2006CB921105, the Programme for Changjiang Scholars and Innovative Research Team in University (PCSIRT), the Programme for New Century Excellent Talents in University under Grant No NCET- 04-0420, the Doctoral Programme of High Education under Grant No 20050269011, Phosphor Programme sponsored by Shanghai Science and Technology Committee under Grant No 06QH14003.
文摘Selective excitation of coherent anti-Stokes Raman scattering from the benzene solution is achieved by adaptive pulse shaping based on genetic algorithm, and second harmonic generation frequency-resolved optical gating (SHG-FROG) technique is adopted to characterize the original and optimal laser pulses. The mechanism for two-pulse coherent mode-selective excitation of Raman scattering is experimentally investigated by modulating the pump pulse in the frequency domain, and it is indicated that two-pulse coherent mode-selective excitation of Raman scattering mainly depends on the effective frequency components of the pump pulse related to specific vibrational mode. The experimental results suggest that two-pulse CARS has good signal-to-background ratio and high sensitivity, and it has attractive potential applications in the complicated molecular system.
基金Supported by the National Natural Science Foundation of China under Grant No 60578049, and the Major Basic Research Project of Shanghai Commission of Science and Technology under Grant No 04dz14001.
文摘We have experimentally demonstrated pulses 0.4 mJ in duration smaller than 12 fs with an excellent spatial beam profile by self-guided propagation in argon. The original 52 fs pulses from the chirped pulsed amplification laser system are first precompressed to 32 fs by inserting an acoustic optical programmable dispersive filter instrument into the laser system for spectrum reshaping and dispersion compensation, and the pulse spectrum is subsequently broadened by filamentation in an argon cell. By using chirped mirrors for post-dispersion compensation, the pulses are successfully compressed to smaller than 12 fs.
基金Supported by the National Science Foundation of China under Grant No 60408008, the Natural Science Key Foundation of Shanghai under Grant No 04JC14036, and the Shanghai Rising-Star Programme.
文摘By means of the numerical solution of time-dependent Schr6dinger equation, we verify a scaling law of photoionization in ultrashort pulses. We find that for a given carrier-envelope phase and duration of the pulse, identical photoionizations are obtained provided that when the central frequency of the pulse is enlarged by k times, the atomic binding potential is enlarged by k times, and the laser intensity is enlarged by ka times. The scaling law allows us to reach a significant control over direction of photoemission and offers exciting prospects of reaching similar physical processes in different interacting systems which constitutes a novel kind of coherent control.
基金Supported by the National Natural Science Foundation of China under Grant No 60578049, and the Major Basic Research Project of Shanghai Commission of Science and Technology under Grant No 04dz14001.
文摘A novel technique for high-power extracavity pulse compression with a nonlinear solid material is demonstrated. Before spectral broadening by self-phase modulation in the solid material, a short filament generated in argon is used as a spatial filter, which works for a uniform spectrum broadening over the spatial profile. Compensated by chirped mirrors, a 15-fs pulse is generated from a 32-fs input laser pulse. A total transmission larger than 80% after the solid material is achieved.
基金Supported by the National Natural Science Foundation of China under Grant No 10574046, the National Basic Research Programme of China under Grant Nos 2006CB806006 and 2006CB921105, the Programme for Changjiang Scholars and Innovative Research Team in University (PCSIRT), the Programme for New Century Excellent Talents in University (NCET-04-0420), the Doctoral Programme of High Education (No 20050269011), the Phosphor Programme of Shanghai Science and Technology Committee (No 06QH14003), and the Shanghai Pujiang Programme (No 06PJ14035).
文摘We theoretically investigate the coherent enhancement of resonant two-photon transitions (TPT) in a three-level atomic system. The TPT can be coherently enhanced by modulating spectral amplitude due to eliminating the destructive interference, though partial laser energy losses. Maximal enhancement of TPT can be achieved by modulating spectral phase due to establishing completely constructive interference. Our research provides a theoretical basis for experimental investigation and appears to have potential application on coherent control in the complicated quantum system.