We apply two-photon resonant nondegenerate four-wave mixing with a resonant intermediate state for the obser- vation of Rydberg states in sodium vapour. The broadening and shift of the sodium 3S- 11D transition pertur...We apply two-photon resonant nondegenerate four-wave mixing with a resonant intermediate state for the obser- vation of Rydberg states in sodium vapour. The broadening and shift of the sodium 3S- 11D transition perturbed by argon are investigated. This technique can achieve Doppler-free resolution of narrow spectral structures of Rydberg levels if lasers with narrow bandwidths are employed.展开更多
With the help of a weak linearly polarized low-frequency field,we study high-order harmonic generation in a circularly polarized high-frequency field.Although the low-frequency field is not intense enough to ionize th...With the help of a weak linearly polarized low-frequency field,we study high-order harmonic generation in a circularly polarized high-frequency field.Although the low-frequency field is not intense enough to ionize the atom,it can accelerate the electron more efficiently.As a result,the application of this field can generate harmonics with a much higher energy compared to.the monochromatic case.展开更多
From the nonperturbative quantum electrodynamics theory, we derive the Landau-Dykhne formula which represents the quantum-mechanical formulation of the three-step model. These studies provide a basis for the classical...From the nonperturbative quantum electrodynamics theory, we derive the Landau-Dykhne formula which represents the quantum-mechanical formulation of the three-step model. These studies provide a basis for the classical-field approaches to high-order harmonic generation and justify some assumptions used in classical-field modelling.展开更多
We demonstrated a phase-sensitive method for studying the Raman-enhanced nondegenerate four-wave mixing(RENFWM).The reference beam is another four-wave mixing signal,which propagates along the same optical path as the...We demonstrated a phase-sensitive method for studying the Raman-enhanced nondegenerate four-wave mixing(RENFWM).The reference beam is another four-wave mixing signal,which propagates along the same optical path as the RENFWM signal.This method is used for studying the phase dispersion of the third-ordersusceptibility X^((3))and for the optical heterodyne detection of the RENFWM signal.展开更多
The effect of fourth-order coherence on ultrafast modulation spectroscopy(UMS)with phase-conjugation geome-try(PCUMS)in a cascade three-level system is investigated using chaotic and phase-diffusion models.It has been...The effect of fourth-order coherence on ultrafast modulation spectroscopy(UMS)with phase-conjugation geome-try(PCUMS)in a cascade three-level system is investigated using chaotic and phase-diffusion models.It has been found that the modulation terms of the beat signal depend on.the second-order coherence function,and different stochastic models of the laser field affect only the fourth-order coherence function.The difference between the PCUMS and UMS is discussed from a physical viewpoint.展开更多
By using the time-independent formal scattering theoretical approach,we develop a nonperturbative quantum electrodynamics theory to describe high-order harmonic generation(HHG).This theory recovers the semi-classical ...By using the time-independent formal scattering theoretical approach,we develop a nonperturbative quantum electrodynamics theory to describe high-order harmonic generation(HHG).This theory recovers the semi-classical interpretation of Corkum(Phys.Rev.Lett.71(1993)1994)and gives the same phenomenological cutoff law.The HHG emission rate is expressed as an analytic closed form.We also discuss the connection between HHG and the above threshold ionization from the scattering viewpoint.展开更多
We study the ellipticity dependence of high-order harmonic generation(HOHG)when a static electric field is present.Through investigating the correspondingclassical trajectories ofthe electronfor the harmonic generatio...We study the ellipticity dependence of high-order harmonic generation(HOHG)when a static electric field is present.Through investigating the correspondingclassical trajectories ofthe electronfor the harmonic generation,it is found that there exists two differentmechanisms.For the elliptical incidence HOHG,we also find that the application of a static electric field can generate harmonics far beyond the usual cutoff.展开更多
Based on the interference between two two-photon processes,we reported a four-level ultrafast modulation spectroscopy in Na vapor,where 3S,3P,5S,and 4D formed a four-level system.We studied the temporal behavior of th...Based on the interference between two two-photon processes,we reported a four-level ultrafast modulation spectroscopy in Na vapor,where 3S,3P,5S,and 4D formed a four-level system.We studied the temporal behavior of the four-wave mixing signal intensity and obtained signal modulation with period 25fs,corresponding to the splitting between 5s and 4D.This technique can achieve Doppler-free precision in the measurement of the energy level splitting between two excited states which are dipolar forbidden from the ground state.展开更多
We study the effects of the static electric field on the high-order harmonic generation(HOHG).It is found that the presence of the static electric field breaks the inversion and reflection symmetry,as a result,the HOH...We study the effects of the static electric field on the high-order harmonic generation(HOHG).It is found that the presence of the static electric field breaks the inversion and reflection symmetry,as a result,the HOHG spectrum exhibits a double plateau structure.Furthermore,the cutoff of the HOHG is no longer corresponding to the maximum kinetic energy the ionized electron can obtain from the laser field.Instead,it corresponds to the maximum kinetic energy of the electron with one return.展开更多
We report experimental studies on the photorefractive response of KNbO_(3) doubly doped with manganese and rubidium,iron and rubidium,respectively.Two-beam coupling response time in KNbO_(3):Mn:Rb is 3 to 10 times sho...We report experimental studies on the photorefractive response of KNbO_(3) doubly doped with manganese and rubidium,iron and rubidium,respectively.Two-beam coupling response time in KNbO_(3):Mn:Rb is 3 to 10 times shorter while the two-beam coupling gain coefficient remains almost the same when compare with that in KNbO_(3):Mn.On the other hand,under similar conditions,two-beam coupling response time in KNbO_(3):Fe:Rb is 6 times faster than that in KNbO_(3):Fe.展开更多
The effects of field correlation on Raman-enhanced nondegenerate four-wave mixing(REN-FWM)have been investigated by examining the RENFWM spectra as a function of time delay between two beams.An enhancement of the rati...The effects of field correlation on Raman-enhanced nondegenerate four-wave mixing(REN-FWM)have been investigated by examining the RENFWM spectra as a function of time delay between two beams.An enhancement of the ratio between the resonant and nonresonant REN-FWM signal intensities was found as the time delay was increased when the laser had broadband linewidth.展开更多
We report a Rayleigh-enhanced nondegenerate four-wave mixing(NFWM)in carbon disulfide.From the Rayleigh-enhanced NFWM spectrum a relaxation time of as short as 220fs was deduced.
Based on the nonperturbative quantum electrodynamics theory of high-order harmonic generation (HHG), we establish a direct connection between above-threshold ionization (ATI) and HHG. HHG can be described simply as an...Based on the nonperturbative quantum electrodynamics theory of high-order harmonic generation (HHG), we establish a direct connection between above-threshold ionization (ATI) and HHG. HHG can be described simply as an ATI followed by laser assisted recombination (LAR). The plateau reflects mainly the characteristic of LAR.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No.19874080。
文摘We apply two-photon resonant nondegenerate four-wave mixing with a resonant intermediate state for the obser- vation of Rydberg states in sodium vapour. The broadening and shift of the sodium 3S- 11D transition perturbed by argon are investigated. This technique can achieve Doppler-free resolution of narrow spectral structures of Rydberg levels if lasers with narrow bandwidths are employed.
基金Supported by the National Natural Science Foundation of China under Grant Nos.69725010 and 69678008the Chinese Academy of Sciences,and the Climbing Program from the Chinese Commission of Science and Technology.
文摘With the help of a weak linearly polarized low-frequency field,we study high-order harmonic generation in a circularly polarized high-frequency field.Although the low-frequency field is not intense enough to ionize the atom,it can accelerate the electron more efficiently.As a result,the application of this field can generate harmonics with a much higher energy compared to.the monochromatic case.
基金Supported by the Chinese Academy of Sciences,the National Natural Science Foundation of China under Grant Nos.69725010 and 69678008the Climbing Program of the National Ministry of Science and Technology of China.
文摘From the nonperturbative quantum electrodynamics theory, we derive the Landau-Dykhne formula which represents the quantum-mechanical formulation of the three-step model. These studies provide a basis for the classical-field approaches to high-order harmonic generation and justify some assumptions used in classical-field modelling.
基金Supported by the National Natural Science Foundation of China under Grant Nos.19874080 and 69578030.
文摘We demonstrated a phase-sensitive method for studying the Raman-enhanced nondegenerate four-wave mixing(RENFWM).The reference beam is another four-wave mixing signal,which propagates along the same optical path as the RENFWM signal.This method is used for studying the phase dispersion of the third-ordersusceptibility X^((3))and for the optical heterodyne detection of the RENFWM signal.
基金Supported by the National Natural Science Foundation of China under Grant No.69978019.
文摘The effect of fourth-order coherence on ultrafast modulation spectroscopy(UMS)with phase-conjugation geome-try(PCUMS)in a cascade three-level system is investigated using chaotic and phase-diffusion models.It has been found that the modulation terms of the beat signal depend on.the second-order coherence function,and different stochastic models of the laser field affect only the fourth-order coherence function.The difference between the PCUMS and UMS is discussed from a physical viewpoint.
基金Supported by the Chinese Academy of Sciences,the National Natural Science Foundation of China under Grant Nos.69725010,69678008,and the Climbing Program from the Chinese Commission of Science and Technology.
文摘By using the time-independent formal scattering theoretical approach,we develop a nonperturbative quantum electrodynamics theory to describe high-order harmonic generation(HHG).This theory recovers the semi-classical interpretation of Corkum(Phys.Rev.Lett.71(1993)1994)and gives the same phenomenological cutoff law.The HHG emission rate is expressed as an analytic closed form.We also discuss the connection between HHG and the above threshold ionization from the scattering viewpoint.
基金Supported by the National Natural Science Foundation of China under Grant Nos.69725010 and 69678008the Chinese Academy of Sciencesthe Climbing Program from the Chinese Commision of Science and Technology.
文摘We study the ellipticity dependence of high-order harmonic generation(HOHG)when a static electric field is present.Through investigating the correspondingclassical trajectories ofthe electronfor the harmonic generation,it is found that there exists two differentmechanisms.For the elliptical incidence HOHG,we also find that the application of a static electric field can generate harmonics far beyond the usual cutoff.
基金Supported by the National Natural Science Foundation of China under Grant No.69578030.
文摘Based on the interference between two two-photon processes,we reported a four-level ultrafast modulation spectroscopy in Na vapor,where 3S,3P,5S,and 4D formed a four-level system.We studied the temporal behavior of the four-wave mixing signal intensity and obtained signal modulation with period 25fs,corresponding to the splitting between 5s and 4D.This technique can achieve Doppler-free precision in the measurement of the energy level splitting between two excited states which are dipolar forbidden from the ground state.
基金Supported by the Chinese Academy of Sciences,the National Natural Science Foundation of China under Grant Nos.69725010,69678008the Climbing Program from the Chinese Commision of Science and Technology.
文摘We study the effects of the static electric field on the high-order harmonic generation(HOHG).It is found that the presence of the static electric field breaks the inversion and reflection symmetry,as a result,the HOHG spectrum exhibits a double plateau structure.Furthermore,the cutoff of the HOHG is no longer corresponding to the maximum kinetic energy the ionized electron can obtain from the laser field.Instead,it corresponds to the maximum kinetic energy of the electron with one return.
基金Supported by the National Natural Science Foundation of Chinathe 863 Project from Chinese Commission of Science and Technologythe Bundesminusterium fur Forschung und Technologie of Germany.
文摘We report experimental studies on the photorefractive response of KNbO_(3) doubly doped with manganese and rubidium,iron and rubidium,respectively.Two-beam coupling response time in KNbO_(3):Mn:Rb is 3 to 10 times shorter while the two-beam coupling gain coefficient remains almost the same when compare with that in KNbO_(3):Mn.On the other hand,under similar conditions,two-beam coupling response time in KNbO_(3):Fe:Rb is 6 times faster than that in KNbO_(3):Fe.
基金Supported by the National Natural Science Foundation of China under Grant No.19474067the Climbing Program from the Chinese Commission of Science and Technology.
文摘The effects of field correlation on Raman-enhanced nondegenerate four-wave mixing(REN-FWM)have been investigated by examining the RENFWM spectra as a function of time delay between two beams.An enhancement of the ratio between the resonant and nonresonant REN-FWM signal intensities was found as the time delay was increased when the laser had broadband linewidth.
基金Supported by the National Natural Sciences Foundation of China,and the Climbing Program from the Chinese Commission of Science and Technology。
文摘We report a Rayleigh-enhanced nondegenerate four-wave mixing(NFWM)in carbon disulfide.From the Rayleigh-enhanced NFWM spectrum a relaxation time of as short as 220fs was deduced.
基金Supported by the Chinese Academy of Sciences,the National Natural Science Foundation of China under Grant Nos.69725010 and 69678008the Climbing Program of the Chinese Commission of Science and Technology。
文摘Based on the nonperturbative quantum electrodynamics theory of high-order harmonic generation (HHG), we establish a direct connection between above-threshold ionization (ATI) and HHG. HHG can be described simply as an ATI followed by laser assisted recombination (LAR). The plateau reflects mainly the characteristic of LAR.
