Abstract: In this paper, the Fabry-Perot etalon is used to multiply the repetition rate of the fiber optical frequency comb. The repetition rate is amplified from 250 MHz to 10 GHz, and the corresponding pulse interval is reduced from 1200 mm to 30 mm. For the pulse cross correlation ranging method, the repetition rate multiplication can greatly reduce the length requirement of the scanning reference arm. We analyze in detail the principle of cross correlation interferometry based on repetition rate multiplication frequency comb. A numerical mode of the function is comprehensively established. The basic parameters of optical source and Fabry-Perot cavity for the influence of filtered optical spectrum and cross correlation fringe are analyzed through the numerical simulation. The multiplied frequency comb is utilized for absolute ranging with the help of a pulse cross correlation method. By comparison, our result differs from the result obtained by a conventional counting interferometer only by 4 μm for distances up to 210 mm.

Abstract: Based on consistent basis set aug-cc-pV5Z, five low-lying potential energy curves and transition dipole moments X2∑+, A2Π, B2∑+, a4Π and b4∑+ of BD+ are calculated by using internally contracted multi-reference configuration interaction approach. According to the calculation results, ro-vibrational levels of theses electronic states are derived through solving the radial Schrödinger equation ro-vibrational equation, and then the molecular parameters, Franck-Condon factors (FCFs) and radiation life are obtained by fitting and calculations. The FCFs (f00=0.923) and radiation life for v"=0 (τ=235 ns) of A2Π-X2∑+ are suitable for achieving rapid laser cooling. Therefore, an optical-cycle for Doppler laser cooling scheme is proposed:the system includes the A2Π1/2(v'=0)-X2∑+(v"=0, 1), where the case of v'=0 contains 2 rotational levels, the cases of v"=0 and v"=1 contain 6 and 4 rotational levels, respectively. According to the proposal, we simulate the dynamic process of the molecular population in laser cooling. The BD+ can be decelerated from initial velocity of 100 m/s to 4.6 m/s (13 mK) after scattering 1150 photons during 5.4 ms.

Abstract: Ultracold Cs2 molecules have been formed by photoassociation. Using the multiphoton ionization technique, we measure the time-evolution of expanding process in ultracold Cs2 molecule system and obtain the decay curve of photoionization signals. Based on a simple case, where the initial distribution of atomic or molecular sample is a Gaussian function of position and of velocity, we get the sample's temperature by theoretical simulation. The result shows a reasonable agreement with the result of release-recapture method in cold atom sample. This method avoids the disadvantage of detecting the weakly fluorescence and can be widely used for measuring the temperature in cold atom or cold molecule system.

Abstract: The single-layered molybdenum disulfide (〈inline-formula〉〈tex-math id="M6"〉\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M6.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M6.png"/〉〈/alternatives〉〈/inline-formula〉) is a two-dimensional nanomaterial with wide potential applications due to its excellent electrical and frictional properties. However, there have been few investigations of its mechanical properties up to now, and researchers have not paid attention to its nonlinear mechanical properties under the multi-fields co-existing environment. The present paper proposed a nonlinear plate theory to model the effect of finite temperatures on the single-layered 〈inline-formula〉〈tex-math id="M7"〉\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M7.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M7.png"/〉〈/alternatives〉〈/inline-formula〉. It is similar to the classical plate theory that both the in-plane stretching deformation and the out-of-plane bending deformation are taken into account in the new theory. However, the new theory consists of two independent in-plane mechanical parameters and two independent out-of-plane mechanical parameters. Neither of the two out-of-plane mechanical parameters in the new theory, which describe the resistance of 〈inline-formula〉〈tex-math id="M8"〉\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M8.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M8.png"/〉〈/alternatives〉〈/inline-formula〉 to the bending and the twisting, depends on the structure’s thickness. This reasonably avoids the Yakobson paradox: uncertainty stemming from the thickness of the single-layered two-dimensional structures will lead to the uncertainty of the structure’s out-of-plane stiffness. The new nonlinear plate equations are then solved approximately through the Galerkin method for the thermoelastic mechanical problems of the graphene and 〈inline-formula〉〈tex-math id="M9"〉\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M9.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M9.png"/〉〈/alternatives〉〈/inline-formula〉. The approximate analytic solutions clearly reveal the effects of temperature and structure stiffness on the deformations. Through comparing the results of two materials under combined temperature and load, it is found, for the immovable boundaries, that (1) the thermal stress, which is induced by the finite temperature, reduces the stiffness of 〈inline-formula〉〈tex-math id="M10"〉\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M10.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M10.png"/〉〈/alternatives〉〈/inline-formula〉, but increases the stiffness of graphene; (2) the significant difference between two materials is that the graphene’s in-plane stiffness is greater than the 〈inline-formula〉〈tex-math id="M11"〉\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M11.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M11.png"/〉〈/alternatives〉〈/inline-formula〉’s, but the graphene’s out-of-plane stiffness is less than the 〈inline-formula〉〈tex-math id="M12"〉\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M12.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M12.png"/〉〈/alternatives〉〈/inline-formula〉’s. Because the 〈inline-formula〉〈tex-math id="M13"〉\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M13.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M13.png"/〉〈/alternatives〉〈/inline-formula〉’s bending stiffness is much greater than graphene’s, the graphene’s deformation is greater than MoS〈sub〉2〈/sub〉’s with a small load. However, the graphene’s deformation is less than the 〈inline-formula〉〈tex-math id="M14"〉\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M14.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M14.png"/〉〈/alternatives〉〈/inline-formula〉’s with a large load since the graphene’s in-plane stretching stiffness is greater than the MoS〈sub〉2〈/sub〉’s. The present research shows that the applied axial force and ambient temperature can conveniently control the mechanical properties of single-layered two-dimensional nanostructures. The new theory provides the basis for the intensive research of the thermoelastic mechanical problems of 〈inline-formula〉〈tex-math id="M15"〉\begin{document}${\rm{Mo}}{{\rm{S}}_2}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M15.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20210160_M15.png"/〉〈/alternatives〉〈/inline-formula〉, and one can easily apply the theory to other single-layered two-dimensional nanostructures.

Abstract: 〈sec〉Radiative shocks are ubiquitous in stellar environments and are characterized by high temperature plasma emitting a considerable fraction of their energy as radiation. Radiative shocks occur commonly in nature, especially in astronomical systems and inertial confinement fusion. The study of the effects of radiation on Richtmyer-Meshkov (RM) instability will improve our ability to understand and predict the evolution of RM instability under high energy density conditions.〈/sec〉〈sec〉A few experiments have been performed to compare the radiative case with the non-radiative case in Rayleigh-Taylor (RT) instability, thereby studying how the radiative effects change the evolution of RT instability, but the interplay between RM instability and radiative shock has been studied rarely. 〈/sec〉〈sec〉This paper reports mainly the role of radiation in the changing of the RM instability. Two experiments are performed at Shenguang III prototype laser facility, the RM instability growth data are obtained by varying the laser intensity. The laser intensity for high-drive experiment is approximately 60% greater than that for low-drive experiment. The target consists of a multiple layer in the axial direction, in which the first layer is a 15μm-thick CH sample serving as an ablator, followed by a 10 μm-thick aluminum used as a shield layer to prevent the preheat effect. The next layer is a 350-μm-thick SiO〈sub〉2〈/sub〉 foam, which is used as a material to produce a radiative shock. The last layer is the CH perturbed sample. There is a sinusoidal perturbation on the surface of CH sample which is adjacent to the SiO〈sub〉2〈/sub〉 foam. The target is irradiated by four overlapping laser beams, and the laser beams produce a large pressure that drives a shock wave, whose velocity can be changed by varying the laser intensity, into the target package.〈/sec〉〈sec〉In the experiments, shock-generated radiative fluxes first ablate the unstable interface which the shock has not passed through, then the shock transmits the unstable interface to produce the RM instability. The images of unstable interface are captured using side-on x-ray radiography, and the experimental results show that the RM growth is suppressed in the experiment for the higher laser intensity. Radiation hydrodynamic code Multi1D is used to evaluate the electron temperature, shock velocity, and electron density. The simulations show that the foam temperature in the high-drive case can reach 80 eV in the front of shock, this energy flows away from the shock front, generating a radiative precursor ahead of the shock. The radiative precursor velocity of 270 km/s is much larger than the shock velocity of 170 km/s, the radiative precursor arrives at the unstable interface before the shock and ablates the unstable interface, so the radiative flux changes the initial conditions of unstable interface. When the shock propagates through the unstable interface, the ablation increases the density gradient length scale and reduces the Atwood number of the unstable interface, so the RM growth is suppressed in the high-drive case because of the ablation of the radiative precursor.〈/sec〉

Abstract: An all-optical high sensitivity atomic magnetometer is investigated and demonstrated experimentally, of which the principle is based on the interaction between laser beam and rubidium atoms in magnetic field. This interaction is dependent on the magnetic field surrounding the Rb atom cell, therefore the magnetic field information can be obtained simply by measuring the changes of the laser power transmitted through the Rb atom cell. The principle of the atomic magnetometer is analyzed and the performance of the experimental setup is investigated. The experimental result agrees well with the theoretical predictions. Furthermore, some important factors that may affect the performance of the magnetometer are discussed, and the ways to improve the sensitivity of the atomic magnetometer are also put forward.

Abstract: The high-fidelity multi-ion entangled states and quantum gates are the basis for trapped-ion quantum computing. Among the developed quantum gate schemes, Mølmer-Sørensen gate is a relatively mature experimental technique to realize multi-ion entanglement and quantum logic gates. In recent years, there have also been schemes to realize ultrafast quantum entanglement and quantum logic gates that operate outside the Lamb-Dicke regime by designing ultrafast laser pulse sequences. In such a many-body quantum system, these entanglement gates couple the spin states between ions by driving either the phonon energy level or the motional state of the ion chain. To improve the fidelity of quantum gates, the modulated laser pulses or the appropriately designed pulse sequences are applied to decouple the multi-mode motional states. In this review, we summarize and analyze the essential aspects of realizing these entanglement gates from both theoretical and experimental points of view. We also reveal that the basic physical process of realizing quantum gates is to utilize nonlinear interactions in non-equilibrium processes through driving the motional states of an ion chain with laser fields.

Abstract: The insulated gate bipolar transistor (IGBT) has developed rapidly as a key power device for medium power application since it was first introduced. It is well known for its relatively low conduction loss and easy gate control. The IGBT is commonly seen in the inductive load application circuit. Due to the large inductive load, the current of the IGBT will stay high until the voltage rises to the bus voltage during the IGBT turn-off. After that, the current starts to decrease and IGBT goes into the tail-current procedure withstanding high voltage. When evaluating the turn-off loss of IGBT, the fall time and the tail current are commonly taken into consideration because these two features are known as good representations of power loss during tail-current procedure. However, the power loss occurring during the voltage rise, which is usually neglected, can also be a significant contributor to the total turn-off loss. The dv/dt determines the voltage rise time and the power loss during this procedure. Thus, predicting the dv/dt is essential for evaluating the power loss during the IGBT turn-off. In this paper, the turn-off transient is divided into four stages and the physical mechanism which determines the dv/dt during the turn-off transient is carefully investigated. An analytical model to characterize the dv/dt during IGBT inductive turn-off is derived based on the calculated miller capacitance values. The functions of the miller capacitance and the dv/dt against time are presented to predict the collector voltage waveform during the IGBT turn-off. To make the model more accurate, the current dependence is considered when calculating the miller capacitance as well as the voltage dependency. The derived model shows that the dv/dt increases nonlinearly with the time going by and can be influenced by several factors, including the drive circuit conditions, the collector current and the carrier concentration profile in the ON-state. Further investigation indicates that the ON-state carrier concentration is greatly influenced by the IGBT cell structure. Thus, the model presented in this paper is effective in both the estimation of IGBT turn-off loss and the guidance of device structure design. The prediction of the derived model shows good agreement with the two-dimensional numerical simulation by Sentaurus TCAD (with the relative error not exceeding 10%) for the IGBT turn-off over a broad range of the collector current values. The device structure simulated in this paper is based on the 650 V/60 A trench-FS-IGBT. The thickness values of the total structure and the buffer layer are 80 m and 20 m, respectively.