Based on a modified coupled wave theory of Kogelnik, we have studied the diffraction of an ultrashort pulsed beam with an arbitrary polarization state from a volume holographic grating in photorefractive LiNbO3 crysta...Based on a modified coupled wave theory of Kogelnik, we have studied the diffraction of an ultrashort pulsed beam with an arbitrary polarization state from a volume holographic grating in photorefractive LiNbO3 crystals. The results indicate that the diffracted intensity distributions in the spectral and temporal domains and the diffraction efficiency of the grating are both changed by the polarization state and spectral bandwidth of the input pulsed beam. A method is given of choosing the grating parameters and input conditions to obtain a large variation range of the spectral bandwidth of the diffracted pulsed beam with an appropriate diffraction efficiency. Our study presents a possibility of using a volume holographic grating recorded in anisotropic materials to shape a broadband ultrashort pulsed beam by modulating its polarization state.展开更多
By using first-principles simulations based on time-dependent density functional theory, the chemical reaction of an HCl molecule encapsulated in C60 induced by femtosecond laser pulses is observed. The H atom starts ...By using first-principles simulations based on time-dependent density functional theory, the chemical reaction of an HCl molecule encapsulated in C60 induced by femtosecond laser pulses is observed. The H atom starts to leave the Cl atom and is reflected by the C60 wall. The coherent nuclear dynamic behaviors of bond breakage and recombination of the HCl molecule occurring in both polarized parallel and perpendicular to the H-Cl bond axis are investigated. The radial oscillation is also found in the two polarization directions of the laser pulse. The relaxation time of the H-Cl bond lengths in transverse polarization is slow in comparison with that in longitudinal polarization. Those results are important for studying the dynamics of the chemical bond at an atomic level.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
A novel model of a hyperbolic two-temperature theory is investigated to study the propagation the thermoelastic waves on semiconductor materials.The governing equations are studied during the photo-excitation processe...A novel model of a hyperbolic two-temperature theory is investigated to study the propagation the thermoelastic waves on semiconductor materials.The governing equations are studied during the photo-excitation processes in the context of the photothermal theory.The outer surface of o semiconductor medium is illuminated by a laser pulse.The generalized photo-thermoelasticity theory in two dimensions(2D)deformation is used in many models(Lord–Shulman(LS),Green–Lindsay(GL)and the classical dynamical coupled theory(CD)).The combinations processes between the hyperbolic two-temperature theory and photo-thermoelasticity theory under the effect of laser pulses are obtained analytically.The harmonic wave technique is used to obtain the exact solutions of the main physical fields under investigation.The mechanical,thermal and recombination plasma loads are applied at the free surface of the medium to obtain the complete solutions of the basic physical fields.Some comparisons are made between the three thermoelastcity theories under the electrical effect of thermoelectric coupling parameter.The influence of hyperbolic two-temperature,two-temperature and one temperature parameters on the distributions of wave propagation of physical fields for semiconductor silicon(Si)medium is shown graphically and discussed.展开更多
High-order harmonic generation of the cyclo[18]carbon(C_(18) ) molecule under few-cycle circularly polarized laser pulse is studied by time-dependent density functional theory. Compared with the harmonic emission of t...High-order harmonic generation of the cyclo[18]carbon(C_(18) ) molecule under few-cycle circularly polarized laser pulse is studied by time-dependent density functional theory. Compared with the harmonic emission of the ring molecule C_(6)H_(6) having similar ionization potential, the C_(18) molecule has higher efficiency and cutoff energy than C_(6)H_(6) with the same laser field parameters. Further researches indicate that the harmonic efficiency and cutoff energy of the C_(18) molecule increase gradually with the increase of the laser intensity of the driving laser or decrease of the wavelength, both are larger than those of the C_(6)H_(6) molecule. Through the analysis of the time-dependent evolution of the electronic wave packets, it is also found that the higher efficiency of harmonic generation can be attributed to the larger spatial scale of the C_(18) molecule,which leads to a greater chance for the ionized electrons from one atom to recombine with others of the parent molecule.Selecting the suitable driving laser pulse, it is demonstrated that high-order harmonic generation in the C_(18) molecule has a wide range of applications in producing circularly polarized isolated attosecond pulse.展开更多
For the first lime, the pressure and flow pulse wave propagation phenomenon is studied in this paper on the basis of he cardiovascular dynamic coupling. E(t)-R model is adopted for left ventricle and T-Y tube model fo...For the first lime, the pressure and flow pulse wave propagation phenomenon is studied in this paper on the basis of he cardiovascular dynamic coupling. E(t)-R model is adopted for left ventricle and T-Y tube model for systemic arteries. Furthermore, impulse response method and Fourier analysis method are employed After reasonable cardiovascular parameters and their value have been selected, the pressure and flow waveforms ape obtained at any poing along the systemic arteries. The results fit measured data well. In addition, the influences of cardiovascular parameters on pulse wave propagation are studied. The work is useful in practice.展开更多
基金Project supported by the State Key Development Program for Basic Research of China (Grant No 2002CCA03500), and the National Natural Science Foundation of China (Grant No 60177016).
文摘Based on a modified coupled wave theory of Kogelnik, we have studied the diffraction of an ultrashort pulsed beam with an arbitrary polarization state from a volume holographic grating in photorefractive LiNbO3 crystals. The results indicate that the diffracted intensity distributions in the spectral and temporal domains and the diffraction efficiency of the grating are both changed by the polarization state and spectral bandwidth of the input pulsed beam. A method is given of choosing the grating parameters and input conditions to obtain a large variation range of the spectral bandwidth of the diffracted pulsed beam with an appropriate diffraction efficiency. Our study presents a possibility of using a volume holographic grating recorded in anisotropic materials to shape a broadband ultrashort pulsed beam by modulating its polarization state.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11074176 and 10976019) and the Doctoral Program of Higher Education of China (Grant No. 20100181110080).
文摘By using first-principles simulations based on time-dependent density functional theory, the chemical reaction of an HCl molecule encapsulated in C60 induced by femtosecond laser pulses is observed. The H atom starts to leave the Cl atom and is reflected by the C60 wall. The coherent nuclear dynamic behaviors of bond breakage and recombination of the HCl molecule occurring in both polarized parallel and perpendicular to the H-Cl bond axis are investigated. The radial oscillation is also found in the two polarization directions of the laser pulse. The relaxation time of the H-Cl bond lengths in transverse polarization is slow in comparison with that in longitudinal polarization. Those results are important for studying the dynamics of the chemical bond at an atomic level.
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funding this research work through the project number(IFP-2020-08).
文摘A novel model of a hyperbolic two-temperature theory is investigated to study the propagation the thermoelastic waves on semiconductor materials.The governing equations are studied during the photo-excitation processes in the context of the photothermal theory.The outer surface of o semiconductor medium is illuminated by a laser pulse.The generalized photo-thermoelasticity theory in two dimensions(2D)deformation is used in many models(Lord–Shulman(LS),Green–Lindsay(GL)and the classical dynamical coupled theory(CD)).The combinations processes between the hyperbolic two-temperature theory and photo-thermoelasticity theory under the effect of laser pulses are obtained analytically.The harmonic wave technique is used to obtain the exact solutions of the main physical fields under investigation.The mechanical,thermal and recombination plasma loads are applied at the free surface of the medium to obtain the complete solutions of the basic physical fields.Some comparisons are made between the three thermoelastcity theories under the electrical effect of thermoelectric coupling parameter.The influence of hyperbolic two-temperature,two-temperature and one temperature parameters on the distributions of wave propagation of physical fields for semiconductor silicon(Si)medium is shown graphically and discussed.
基金Project supported by the National Key Research and Development Program of China (Grant No.2019YFA0307700)the National Natural Science Foundation of China (Grant Nos.12204214,12074145,and 11627807)。
文摘High-order harmonic generation of the cyclo[18]carbon(C_(18) ) molecule under few-cycle circularly polarized laser pulse is studied by time-dependent density functional theory. Compared with the harmonic emission of the ring molecule C_(6)H_(6) having similar ionization potential, the C_(18) molecule has higher efficiency and cutoff energy than C_(6)H_(6) with the same laser field parameters. Further researches indicate that the harmonic efficiency and cutoff energy of the C_(18) molecule increase gradually with the increase of the laser intensity of the driving laser or decrease of the wavelength, both are larger than those of the C_(6)H_(6) molecule. Through the analysis of the time-dependent evolution of the electronic wave packets, it is also found that the higher efficiency of harmonic generation can be attributed to the larger spatial scale of the C_(18) molecule,which leads to a greater chance for the ionized electrons from one atom to recombine with others of the parent molecule.Selecting the suitable driving laser pulse, it is demonstrated that high-order harmonic generation in the C_(18) molecule has a wide range of applications in producing circularly polarized isolated attosecond pulse.
文摘For the first lime, the pressure and flow pulse wave propagation phenomenon is studied in this paper on the basis of he cardiovascular dynamic coupling. E(t)-R model is adopted for left ventricle and T-Y tube model for systemic arteries. Furthermore, impulse response method and Fourier analysis method are employed After reasonable cardiovascular parameters and their value have been selected, the pressure and flow waveforms ape obtained at any poing along the systemic arteries. The results fit measured data well. In addition, the influences of cardiovascular parameters on pulse wave propagation are studied. The work is useful in practice.