Electromagnetically induced transparency (EIT) is the basis of measuring microwave by Rydberg atom, and the spectral characteristics of EIT affect the measurement accuracy of microwave field directly. The effects of the Rabi frequency of a coupling laser, Rabi frequency of a probe laser, and temperature of an atomic chamber on the electromagnetically induced transparency spectral characteristics of cesium atoms were investigated experimentally in this study. The causes for the variations in optical bistability, atomic collisions, and atomic density are investigated. The research results indicate that as the Rabi frequency of the coupling laser increases, both the width and the degree of asymmetry of the EIT spectrum first increase and then stabilize. In addition, as the Rabi frequency of the probe laser increases, the width of the EIT spectrum increases monotonically. The fitting slope initially increases and then stabilizes as the Rabi frequency of the coupling laser increases, whereas the degree of asymmetry has two trends: increasing, decreasing, and increasing, decreasing, increasing; as the temperature of the atomic chamber increases, both of them first increase and then decrease. This study is beneficial for optimizing the experimental parameters of quantum microwave measurement, improving the sensitivity of microwave measurement, and facilitating the practical application of the technology for quantum microwave measurement.

The generation of high-order harmonics from planar molecules H32+ with different molecular configurations is studied using the numerical solution of the time-dependent Schr?dinger equation. The results show that planar molecules H32+ emit both odd and even harmonics, and the relative yields of odd and even harmonics are sensitive to orientation angles and molecular configuration. A simple method is proposed, based on the above results, to detect the position of atomic nucleus via odd and even high-order harmonic spectra. Bond lengths and angles from oriented asymmetric planar molecules can be reconstructed using odd-even harmonics at different angles. Meanwhile, probing the polycentric molecular structure in attoseconds using a high-order harmonic spectrum is helpful.

Doping of silicon clusters with transition metals can enhance the stability of such clusters and confer many peculiar physical and chemical properties. Therefore, this method occupies an important position in the fields of new energy and materials science. Herein, we report the geometric structures as well as electronic and thermodynamic properties of CoSi16- and Co2Si322- clusters using the particle swarm optimization algorithm CALYPSO searching method and density functional theory. Results indicate that the lowest structures of the CoSi16- and Co2Si322- clusters exhibit the highly symmetric D2d and D2h point structures, respectively, in which the Co atom is completely encapsulated in Si cages. Based on these structures, various electronic properties, including the magnetic properties and bond order, are systemically evaluated. In addition, the photoelectron spectra, infrared spectra, and Raman spectra are recorded to identify the main characteristic peaks of the two systems. Finally, the thermodynamic properties of the two systems are investigated. Moreover, the temperature dependence of Cv and S for the CoSi16- and Co2Si322- clusters is discussed.

The potential energy curves for seven Λ-S electronic states (X2Σ+, B2Σ+, C2Δ, F2Σ+, A2Π, D2Π, and E2Π) of strontium chloride (SrCl) molecule are investigated using the multireference configuration interaction method (MRCI). Davidson correction (+Q), core-valence correction, and spin-orbit coupling effect are considered in the calculation. Based on the obtained potential energy curves of Λ-S states, the vibration energy levels, wave functions, and spectroscopic parameters are determined by solving the Schrödinger equation using the discrete position presentation method. The calculated values agree substantially with experimental and theoretical values. Additionally, the transition dipole moments, Franck-Condon factors, and radiative lifetime of the SrCl molecule are explored. Due to the significant diagonal distribution of the Franck-Condon factors (f00=0.96959) and short radiative lifetimes (τ=31.05 ns) of the A2Π (ν′=0) →X2Σ+(ν″=0) transition, the SrCl molecules are suitable for rapid laser cooling. Therefore, this study presents a three-laser scheme for laser cooling of SrCl molecules. The calculated pump and repump wavelengths of the laser-driven cycling are668.2 nm (λ00), 682.0 nm (λ01), and 681.5 nm (λ12).

Density functional theory (DFT) and time-dependent density functional theory (TDDFT) at the B3LYP/6-311+G(d, p) level were used to calculate and optimize the physical characteristics of 4-bromophenol under the different electric fields, including the bond length, bond angle, total energy, dipole moment, energy gap, infrared spectrum, dissociation properties, and excited state. The results revealed a significant change in the molecular structure of 4-bromophenol under an external electric field (0-0.03 a.u.). The molecular C—Br bond length, O—H bond length, and dipole moment increased gradually with increasing external electric field, while the C—O bond length, total energy, and energy gap decreased gradually. The four absorption peaks of the molecular infrared spectrum showed a red shift. Simultaneously, the first 10 excited states also showed a red shift. When the external electric field intensity was 0.03 a.u., the potential barrier disappeared, and molecular dissociation was observed.

We theoretically investigate the high-order harmonic generation from acceptor-doped semiconductors by numerically solving the one-dimensional time-dependent Schr?dinger equation based on the single electron approximation. The results show that the harmonic efficiency of the second plateau from acceptor-doped semiconductors is about three to four orders of magnitude higher than those from undoped semiconductors. Theoretical analysis shows that doping changes the energy-band structure of the semiconductor, narrows the band gap between the valence band and the first conduction band, and between the first conduction band and the second conduction band. Then it is easier for electrons to tunnel into the higher conduction band, and the electron population of the high conduction band is increased, thus the harmonic efficiency of the second plateau is improved.

The transient absorption properties of Rydberg atoms driven by two pulsed laser fields are investigated herein on the basis of the theory of density matrix equation, which describes the interaction of photon and material. It is found that owing to the weak coupling field, the probe absorption first increases to the maximum value and then decreases monotonically to zero with time. The maximum value of the probe absorption increases with an increase in Rabi frequency until the largest value is obtained. Then, it decreases gradually and the absorption with time presents the character of oscillation at the same time. When the coupling field's Rabi frequency is appropriate, the phenomenon of negative absorption occurs. The analysis of the evolution of population and the coherent term with time reveals that the coherent term caused by the influence of the coupling and probe field results in a negative absorption.

By accurately solving the full-dimensional time-dependent Schr?dinger equation (TDSE), the dynamic interference effects in the ionization of atomic hydrogen by chirped laser pulses with different polarizations are numerically studied. The emphasis is put on the influences of the chirp parameters on the dynamic interference patterns of the photoelectron energy spectra. Numerical results show that the increase of the chirp will cause the suppression of dynamic interference pattern in three polarization cases; for any chirp parameter, the interference subpeaks show a rightward shift when the ellipticity of the pulse increases; for any chirp parameter, the dynamic interference pattern will disappear when the laser pulse is up to 30 fs, indicating that the previously reported calculation of one-dimensional TDSE cannot accurately describe the real physical process.

The 42D Rydberg atom is prepared in cesium vapor at room temperature, and the power-frequency electric field is measured based on the electromagnetically induced transparency spectrum of Rydberg atom. The 42D Rydberg atom is prepared by two-photon excitation, and the stepped electromagnetically induced transparency spectrum is obtained by changing the coupling frequency. The relationship between the spectral frequency shift and splitting of Rydberg atom under radio frequency(RF) electric field and the amplitude and frequency of RF electric field is studied. By modulating the amplitude of power-frequency electric field to RF electric field, the measurement of power-frequency electric field intensity and frequency is realized. Research results has important reference value and significance for online traceable measurement of power-frequency electric field.

In order to extend the measurement of the nonlinear effect intensity to the fifth-order nonlinear, the fifth-order nonlinear effect in the electromagnetically induced transparency system is studied theoretically. The research results show that the quantum coherence effect greatly enhances the nonlinear effects of electromagnetically induced transparency system, including susceptibility of third-order nonlinear which can simulate Raman scattering and four-wave mixing, fifth-order nonlinear susceptibility with two completely different nonlinear absorption and dispersion.The fifth-order cross nonlinearity of the nonlinear absorption excites the four-photon absorption and the fifth-order cross nonlinearity of the nonlinear gain excites the super Raman scattering. The fifth-order cross nonlinearity of the electric polarization of the nonlinear absorption excites the six-wave mixing.

In this study, we investigated the single-path and multipath conversions of ultracold bosonic heteronuclear tetra-atomic molecules using the generalized stimulated Raman adiabatic passage technique. First, we established a mean-field model and obtained the corresponding dark state solutions and two-photon resonance conditions. Next, we compared the molecule conversion dynamics of the single-path and multipath cases and found that constructive interference effects existed in the multipath cases; this could increase the molecular conversion rate. In particular, for the three-path scheme, the interference effect was obvious and the conversion rate was high. We further studied the influence of external field parameters on the conversion rate of the multipath scheme by varying the pulse intensity and found that the influence had two sides: constructive and destructive interference, respectively, which increased and decreased the conversion rate of molecules.

Based on the ladder-type atomic system of cesium ( 133Cs) 6S1/2-6P3/2-6D5/2, a pump light with a wavelength of 852.335 nm or 852.356 nm and probe light with a wavelength of 917.483 nm were inversely arranged in a 133Cs vapor cell at room temperature. Accordingly, a double resonance absorption spectrum of 6P3/2-6D5/2 hyperfine energy level transition with narrow line-width and high signal-to-noise ratio is obtained. Subsequently, all the frequency intervals of the hyperfine energy level splitting structure of the excited state 6D5/2 are measured using a “ruler” built with an acousto-optic modulator. Finally, the hyperfine constants of magnetic dipole Ahfs and electric quadrupole Bhfs are obtained as (-4.59±0.06) and (-0.78±0.66) MHz, respectively, which agree with values reported in the literature.

Based on the frequency-domain theory in nonperturbative quantum electrodynamics, we investigate the above-threshold ionization of an atom exposed to two-color laser fields of different frequencies. As both the frequencies of two laser fields are lower than the ionization potential of the atom, the above-threshold ionization spectrum comes from quantum interference among many ionization channels, and the two laser fields play same roles in the above-threshold ionization process. As the frequency of one of the two laser fields increases, the above-threshold ionization spectrum shows a multiplateau structure gradually, which is from the contribution of atoms absorbing different photons of high-frequency laser field. As the frequency of one of the two laser fields is much higher than the atomic ionization potential, the two laser fields play different roles in the above-threshold ionization process, where the high-frequency laser field may determine the ionization probability and the low-frequency laser field may determine the width of each plateau that can be predicted by the energy conservation relationship.

By using the improved strong field approximation method combined with the time window function, the effect of hydrogen atomic electron wavepacket (EWP) interference in above-threshold ionization by a strong laser field on the photoelectron energy spectra and two-dimensional (2D) momentum spectra is analyzed. It is found that the general characteristics of photoelectron energy spectra and 2D momentum spectra are formed by the interplay of inter-cycle and intra-cycle interferences. The fanlike structure in the 2D momentum spectra is caused by the long-range Coulomb potential and the intra-cycle interference. A numerical solution of the time-dependent Schr dinger equation (TDSE) is used to analyze the reason why the intra-cycle interference is suppressed in multi-cycle pulse ionization and it is found that this special fringe appears in the 2D momentum spectra only when the Keldysh parameter is close to 1. These results show that the long-range Coulomb potential has an important influence on the formation of these fringes.

Using the strong field approximation method combined with the time window function, the two-dimensional (2D) momentum spectra of hydrogen atoms for above-threshold ionization by a few-cycle intense laser field were calculated and compared with the results obtained by the Coulomb-Volkov approximation combined with the time window function. It is found that the fanlike structures in the 2D momentum spectra are formed as a result of the interplay of intracycle and intercycle interferences under the action of a long-range Coulomb potential. In addition, the 2D momentum spectra of hydrogen atoms under different pulse durations were calculated by solving the time-dependent Schr dinger equation and it is found that some special fringe structures appear in the 2D momentum spectra beyond the intracycle and intercycle interference fringes. These structures are formed by the rescattered electron wave packets.

Frequency stability is an important indicator to evaluate the performance of a coherent population trapping (CPT) atomic clock, and the type and pressure ratios of the buffer gas compositions inside an atomic vapor cell are main factors influencing frequency stability. In this study, the temperature frequency shift caused by buffer gas compositions, i.e., Ar and N2, was simulated and analyzed theoretically, and the temperature shifts caused by different pressure ratios of buffer gas compositions were tested experimentally. The optimal ratio of buffer gas compositions in the atomic vapor cell was determined based on the theoretical and experimental results, and the corresponding operation point for the minimum temperature frequency shift was found. The research results provide a valuable reference for selecting the pressure ratio of buffer gas compositions and the operation temperature of the atomic vapor cell for a CPT atomic clock.

Using the improved strong field approximation method, the effects of long-range potential and short-range potential in above-threshold ionization energy spectra are investigated and the origin of the low-energy structure is also found. Meanwhile, in order to prove whether it is reasonable to use pure molecules instead of molecular ions in calculating the differential cross sections (DCS) of electrons and molecular ions, the DCS of electrons and atomic ions are calculated in some different incident electron energies conditions. The results of theoretical calculation and experiments show that the effect of long-range potential can be neglected and using pure molecules instead of molecular ions is reasonable with large-angle scattering in the large incident electron energies condition.

The non-sequential double ionization of magnesium atom in elliptically polarized strong laser field is investigated with the classical ensemble method. The non-sequential double ionization occurs in elliptically polarized strong laser field for magnesium atom, and the ionization rate decreases a little with the increase of ellipticity. Back analysis of the non-sequential double ionization trajectories shows that the decrease of the number of returning electrons results in the decrease of ionization rate. In addition, the distributions of the correlated two-electron transverse momentum and counts of electron with different energies demonstrate the kinetic energy of ionized electrons rises with the increase of ellipticity, so the second electron can be ionized easily with the recollision of the returning electron, which can compensate the reduced ionization rate, and thus the ionization rate does not decrease too much.

On the basis of recent experiment, the focusing and leading effect of an ultra-cold Bose-Einstein condensate (BEC) is theoretically investigated when it transversely passes through a red-detuned Gaussian field. Particular attentions are paid on the focusing (or defocusing) in shape and leading (or lagging) in position of the atoms, which are induced by a red-detuned (or blue-detuned) laser field. The time-dependent motion of BEC atoms and its final status are presented under the influences of the acceleration, the dipolar interaction between atom and optical field, as well as the s-wave scattering collisions of individual atoms. In addition, the acceleration only influences position of the atoms; an attractive or repulsive s-wave interaction can bring on a strong deformation to the atoms, making them collapse or diffusion in essence. Compared to the previous experiments, the findings are well consistent in the regime of a red-detuned laser field, moreover, an extension to the blue-detuned field is predicted. The results may provide more feasible ways for studying coherent atom-light manipulations in the field of ultra-cold atoms and molecules in the future.

In order to improve the computational efficiency of synthetic aperture imaging algorithm in the medical endoscopic ultrasound system, the synthetic aperture imaging approach with parallel implementation on graphics processing unit (GPU) is proposed. Firstly, the basic principle and image reconstruction process of synthetic aperture algorithm are introduced. Then, the algorithm is analyzed in parallel processing. Finally, synthetic aperture imaging algorithm for endoscopic ultrasound based on GPU is implemented by using the flexible architecture of single instruction multiple threads (SIMT) of compute unified device architecture (CUDA) programming mode. Multiple simulation experiments of scattering points imaging are compared and analyzed, and the imaging experiment verifications of iron wire, cyst prosthesis and pigskin tissue are carried out by using a self-built endoscopic ultrasound experimental system. The experimental results show that the proposed method can greatly improve the computational efficiency while keeping the same imaging quality and results. When the calculated data size is 1.47 GB (5305×581×64×8 byte), the maximum speedup ratio reaches 50.93.

Based on the temperature measurement principles of double line of atomic emission spectrum, the photoelectric pyrometer based on silicon photomultiplier is proposed, and the structure and temperature measurement principle of the photoelectric pyrometer are introduced. Al I 690.6 nm and Al I 708.5 nm are selected from the atomic spectra database as the temperature measurement element spectral lines. The temperatures of aluminum burnt in pure oxygen are obtained by photoelectric thermometer and compared with temperatures measured by the thermocouple. The results show that the average relative error of temperatures measured by the two methods is 1.5%, which proves the feasibility of the proposed method.