Three-dimensional atom localization in a five-level M-type atomic system

By using three mutually perpendicular standing-wave fields, we propose a scheme for three-dimensional (3D) subwavelength atom localization in a five-level M-type atomic system. Based on the electromagnetically induced transparency, position probability distribution of the atom in 3D space could be determined via measuring the probe absorption which is proportional to the filter function. It is shown that patterns of 3D atom localization depends sensitively on the coupling schemes of the standing-wave fields. When the standing-wave fields couple three different transitions, the same atom localization patterns are formed in the eight subspaces of the 3D space. While all the standing-wave fields are applied on one transition, we can realize different atom localization patterns in the eight subspaces. From the view of the xy plane, various symmetric or asymmetric atom localization patterns could be formed at different z positions by adjusting the parameters of the laser fields.     

EIT-based MZ-MMI all-optical switch

We propose a new control structure for all-optical switching in multimode inference (MMI)-based Mach–Zehnder interferometer (MZI) devices. This structure is composed of an MZI doped by three-level nanocrystals for the realization of electromagnetically induced transparency (EIT) in the lower arm. We use two different intensities of control field for two states of the proposed switch. Using a control field in both of the two switching states is necessary, where the EIT region is transparent. By changing the intensity of the control field, the refractive index of the doped region changes, which makes the phase difference between the two arms of the MZI. Hence, the switching operation takes place. Simulation results show that the extinction ratio of the device is ?32dB in the worst case.     

Destructive and constructive interference in the coherently driven three-level systems

Destructive and constructive interference in the Autler–Townes three-level systems is studied in the dressed state basis. The dependence of the interference on the spontaneous emission and dephasing reservoirs is analyzed. The strong field correlates or anti-correlates the random phase caused by the reservoirs. The correlation reduces and the anti-correlation enhances the absorption. Each of the interference pathways is formed by two processes, stimulated absorption and spontaneous emission. The interference effect can be neglected if the Rabi frequency of the strong field is larger than the decay rates.     

Electromagnetically induced transparency in a quadratically coupled optomechanical system with an atomic medium

We investigate a quadratically coupled optomechanical cavity system filled with a two-level atomic medium. The output of the cavity field exhibits analogous electromagnetically induced transparency when the optomechanical system interacts with the coupling and probe fields, respectively. We show that the introduction of the atomic medium can enhance the fluctuation of the displacement of the membrane as well as its energy. With the increasing of the atomic number, the dip of the absorption becomes deep.     

Phase time delay and Hartman effect in a one-dimensional photonic crystal with four-level atomic defect layer

The Hartman effect is revisited using a Gaussian beam incident on a one-dimensional photonic crystal (1DPC) having a defect layer doped with four-level atoms. It is considered that each atom of the defect layer interacts with three driving fields, whereas a Gaussian beam of width w is used as a probe light to study Hartman effect. The atom–field interaction inside the defect layer exhibits electromagnetically induced transparency (EIT). The 1DPC acts as positive index material (PIM) and negative index material (NIM) corresponding to the normal and anomalous dispersion of the defect layer, respectively, via control of the phase associated with the driving fields and probe detuning. The positive and negative Hartman effects are noticed for PIM and NIM, respectively, via control of the relative phase corresponding to the driving fields and probe detuning. The advantage of using four-level EIT system is that a much smaller absorption of the transmitted beam occurs as compared to three-level EIT system corresponding to the anomalous dispersion, leading to negative Hartman effect.     

Switching enhancement and suppression of four-wave mixing via a dressing field

The switch between the enhancement and suppression of the four-wave mixing (FWM) process in an electromagnetically induced transparency (EIT) window via quantum interference has been demonstrated experimentally. The enhancement and suppression of the FWM signal, as well as the EIT window, switch with a change in the probe detuning. Also, by controlling the powers of the dressing and probe fields, the enhancement and suppression of the FWM signal can be switched and an optimized enhancement can be obtained. Such a switch of the enhancement and suppression of the FWM signal intensity can find potential applications in optical switches, optical communication and quantum information processes.     

Talbot effect of selective reflection from a homogeneous atomic vapour

In the present work, the Talbot effect of selective reflection (SR) modified by the coupling fields is examined. It is shown that SR Talbot (SRT) patterns can be dramatically modified by the detuning, the strength and the incident angles of the coupling fields. SRT patterns at the integer and the half integer planes are similar to conventional Talbot images. However, the manifest change in fractional SRT patterns can be observed at several planes, e.g. at the quarter and the three quarters planes, the spatial frequency of those patterns is doubled comparing to that of the original output plane, and the carpets become blurring with an increasing asymmetry as the coupling fields are detuned away from the resonant transition of atoms, or as its strength increases. These peculiar Talbot patterns are mainly from a combined contribution of real and imaginary parts of source SR field modified by the coupling light. The SRT images may have potential applications in the detection of atom–surface interactionsand the processing of optical information.     

Plasmonic analog of electromagnetically induced transparency in planar metamaterials: manipulation and applications

In this article, we have investigated an analog of electromagnetically induced transparency (EIT) in planar metamaterials by a metallic regular triangle (RT) embedded in split ring (SR) nanostructure. It is demonstrated that, depending on the different coupling ways between the RT and the SR, the EIT-like spectral response can be actively modulated by simply adjusting the incident light polarization angle. Based on this observation, an on-to-off active modulation of the EIT-like transparency window can be realized, and it can serve as the base for an optical switching with the switching efficiency exceeding 95%. The size of the RT finely controls the coupling strength between the RT and the SR. It is shown that the EIT-like transparency window can be enhanced or suppressed by adjusting the size of the RT, which shows the big modulation to the EIT-like spectral response. Furthermore, the transmission spectra show potential applications in sensing due to high sensitivity of about 600 nm/RIU with figure of merit exceeding 36 to the surrounding environment.     

Coherent Superposition of Electric- and Magnetic-Dipole Spin-Flip Transitions in Zinc Blende Semiconductors

Spin resonance (SR) studies offer an important and unique opportunity for investigating coherent superposition of electric-and magnetic-dipole spin-flip transitions in semiconductors. We will focus on far-infrared studies of conduction-electron spin-flip transitions in narrow-gap semiconductors, where this effect is most clearly evident. Although the SR transition is normally electric-dipole-forbidden, it is well known that there exist mechanisms (e.g., nonparabolicity and inversion asymmetry) that relax these selection rules. In comparing the relative importance of these mechanisms, it will be shown that the combination of spin–orbit coupling and inversion asymmetry (as developed by E. I. Rashba and V. I. Sheka) is the dominant process allowing electric-dipole-induced spin-flip transitions. In this review, special attention will be given to the interference of the electric- and magnetic-dipole matrix elements, which provide a unique opportunity for determining the inversion-asymmetry parameter (including its sign) in zinc blende narrow-gap semiconductors. This effect can also serve as a basis for observing spin-based electromagnetically induced transparency—a phenomenon of considerable contemporary interest from both fundamental and applied viewpoints.     

Cross-phase modulation and population redistribution in a periodic tripod medium

The cross-Kerr effect is studied for two weak beams, probe and trigger, propagating in an atomic medium in a tripod configuration, dressed by a strong standing wave coupling beam in a regime of electromagnetically induced transparency. The nonlinear phase shifts for both transmitted and reflected probe beams induced by the trigger's presence are found to depend on the probe detuning, the control beam's intensity, the relaxation rates and, in particular, on the redistribution of the population among the atomic levels. Such a quantitative analysis indicates that the transmitted and reflected probe beam components and their respective phase shifts can be easily controlled and optimized.     

Exhibition of subluminal solitons in a four-level atomic system with two-folded levels

With one weak probe, one strong pumping and one control field, the group velocity dispersion can be balanced by the Kerr effects in a lifetime-broadened four-level atomic medium with two folded levels with proper parameters. This results from the subluminal optical solitons that are formed. Additionally, the conditions for which subluminal solitons occur are given.     

Kerr nonlinearity and optical multi-stability in a four-level Y-type atomic system

The nonlinear response to applied fields of a four-level Y-type atomic system is investigated. The effect of laser intensity and quantum interference induced by spontaneous emission on optical bistability, optical multi-stability and Kerr nonlinearity is then discussed. It is found that the threshold of the optical bistability can substantially be reduced by the quantum interference. So, an enhanced Kerr nonlinearity with reduced absorption can be achieved.     

Sub- and superluminance with gain in a three-level ladder-type atomic system with spontaneously generated coherence

The effects of spontaneously generated coherence (SGC) on the propagation of a weak probe pulse are investigated in a ladder-type atomic system. Due to SGC, the properties of the dispersion and the absorption of a three-level ladder-type system are changed greatly. With proper parameters, the system can produce normal and anomalous dispersion regions in the gain region. The effects of the incoherent pumping and the relative phase on the group velocity are also studied. They all can be used as switches to manipulate the group velocity of the weak probe field from gain-assisted sub- to superluminance.     

Tunneling-induced high gain and narrow linewidth of a cavity with an asymmetric quantum-well system

A scheme is proposed for obtaining high gain and narrow linewidth of a cavity with an asymmetric quantum-well system. Due to resonant tunneling, destructive interference for linear absorption leads to a tunneling-induced transparency window which compresses the cavity linewidth; moreover, constructive interference for cross-nonlinear susceptibility occurs, which introduces high gain and large dispersion, and the cavity linewidth is much compressed. In the latter case, the intensity of cavity transmission could be enhanced one order of magnitude larger than that of input field, and its linewidth could be one-seventieth of the empty cavity.     

流动聚焦微气泡流型分布及控制参数实验

介绍了一种基于毛细管流动聚焦方法制备微纳米量级气泡的流动聚焦微流控芯片．以水和空气为工质,在一定的压力和流量下,利用高速摄影技术研究微气泡的尺寸、发生频率和形成过程．分析了表面张力、气体压力、液体流量等参数对微气泡直径和发生频率的影响．实验结果表明,该微流控芯片可以稳定产生直径微米量级的微气泡,操作简单,在微反应器和生物、医药等领域有良好的应用前景．     

Interaction dynamics of Bragg grating solitons in a semilinear dual-core system with dispersive reflectivity

The interactions of quiescent Bragg grating (BG) solitons in a semilinear dual-core system, where one core is nonlinear and is equipped with a BG with dispersive reflectivity and the other core is linear are investigated. It has been previously shown that the model supports stable quiescent solitons which may or may not have sidelobes in their profiles. The interaction of in-phase solitons can lead to various outcomes such as generation of two moving solitons with equal or unequal velocities, merger of solitons into a quiescent one, generation of three solitons (one quiescent and two moving ones) and destruction of solitons. The presence of sidelobes can radically change the interaction dynamics, e.g. in-phase solitons can repel or form a temporary bound state which subsequently splits into two separating solitons. We have identified the outcome regions for in-phase interactions through systematic numerical simulations in the plane of dispersive reflectivity vs. frequency. We have also analysed the effect of initial separation on the outcomes of interactions. It is found that when sidelobes are present in solitons’ profiles, the outcomes of the interactions are strongly dependent on the initial separation.     

梁与正交各向异性板弯曲波的传递特性研究

以正交各向异性板与各向同性梁耦合系统弹性波传递特性为研究对象,基于弯曲波传播的动力学分析,推导出子系统间的功率流传递系数(power flow transmission coefficient,PTC)和耦合边界处的耦合损耗因子(coupling loss factor,CLF)表达式.计算分析了内损耗因子、频率和方向...     

Reduction of residual stress and deformation in electron beam welding by using multiple beam technique

The electron beam could be controlled by magnetic field for fast deflection, in which way multi-beam could be produced by deflection technique. The multi-beams run simultaneously for material processing with different heat input and positions. Therefore, it is possible to adjust the thermal effects and optimize the process. In this paper, the generation of multi-beams in electron beam welding (EBW) was investigated, and the processes of EBW with multi-beams were also investigated by both the numerical simulation methods, i.e., finite element analysis (FEA), and the experiments. The result shows that the residual stress of EBW could be minimized by using the multiple beam technique, and at the same time the welding deformation could also be reduced with the optimized parameters.