Broadband acoustic focusing by symmetric Airy beams with phased arrays comprised of different numbers of cavity structures

We realize broadband acoustic focusing effect by employing two symmetric Airy beams generated from phased arrays,in which the units of the phased arrays consist of different numbers of cavity structures, each of which is composed of a square cavity and two inclined channels in air. The exotic phenomenon arises from the energy overlapping of the two symmetric Airy beams. Besides, we demonstrate the focusing performance with high self-healing property, and discuss the effects of structure parameters on focusing performance, and present the characteristics of the cavity structure with straight channels. Compared with other acoustic lenses, the proposed acoustic lens has advantages of broad bandwidth(about 1.4 kHz), high self-healing property of focusing performance, and free adjustment of focal length. Our finding should have great potential applications in ultrasound imaging and medical diagnosis.     

基于耦合开口方环共振空腔的可控法诺共振研究

基于表面等离子激元理论与金属-介质-金属波导结构提出一个由开口方环共振空腔、挡板及MIM波导组成的波导结构,并使用有限元方法系统地研究了该结构的透射特性.仿真计算结果表明:该结构可以产生法诺共振现象,其共振波长可以通过改变开口方环空腔的长度及开口大小进行调节,该结构敏感度可达1 600nm/RIU,品质因数为1.31×10~5.此外,通过调整方环共振空腔上开口的位置,在波导中产生了双重法诺共振现象,其敏感度可达1 700nm/RIU,品质因数为8.3×10~4.该结构有望在光学集成回路,尤其是纳米生物传感器方面得到比较广泛的应用.     

截卵形弹水平入水的速度衰减及空泡扩展特性

用轻气炮设备对截卵形弹进行了速度在100~150 m/s的水平入水实验,利用高速相机记录了整个入水过程,获取了截卵形弹体在水中运动的速度衰减规律,并对平头弹、卵形弹及截卵形入水弹道稳定性及速度衰减规律进行了对比,对截卵形弹体入水形成的空泡扩展行为进行了理论研究,建立了关于空泡扩展的理论模型,得到了固定位置和固定时间处空泡扩展半径、速度分别与时间和侵彻距离的关系,实验数据与理论计算吻合很好。     

Dynamics of a rigid body with an ellipsoidal cavity filled with viscous fluid

We revisit the approach proposed by F.L.  Chernousko to modeling the dynamics of a rigid body with a cavity entirely filled with a highly viscous fluid. Within the approach, a finite-dimensional model of the body+fluid system is offered and the influence of the fluid is represented as a special torque acting upon the body with solidified fluid. Our aim is to develop further and expand a few technical aspects of the Chernousko model. In particular, we offer a coordinate-free form for some essential formulas and consider the case of constrained dynamics. To illustrate the results obtained we explore the motion of a physical pendulum with a fluid-filled cavity on a rotating platform.     

双光力诱导透明窗口的可调特性

提出一个杂化腔光力系统理论方案,利用两纳米机械振子间的库仑耦合作用实现弱探测光的双光力诱导透明窗口.研究边带可分辨区域和红失谐情况下双光力诱导透明窗口的可调特性.数值计算表明:两纳米振子间的库仑作用可有效地使单光力诱导透明窗口劈裂为双透明窗口.随着库仑耦合强度的增大,两透明窗口间的距离对称性地拉大;其次,光力腔衰减率的改变对两透明窗口的位置和深度无影响,仅对两透明窗口的宽度产生细微改变,测量精度可在坏腔情形下得到很好的保持;另外,仅增加参量放大器的非线性增益参量将使两透明窗口变宽,而引入驱动参量放大器的光场相位,利用相位匹配可以产生比空腔情形更加狭窄陡峭的双透明窗口,可用于比空腔情况更加精密的测量.     

光学腔内两正交偏振模振幅和相位的补偿

本文开展了光学腔内两正交偏振模振幅和相位补偿的实验研究。通过采用特殊腔型和两个λ/2波片,补偿腔内反射镜对水平偏振模和垂直偏振模的反射率差异,使两个偏振模的输出振幅相等。利用一组λ/4-λ/2-λ/4波片补偿光学腔内水平偏振模和垂直偏振模的相位差,使两个模的输出重合。通过上述的振幅和相位补偿方法,可实现任意偏振光经过环形腔后偏振不变,为任意偏振比特在腔内冷原子系综中的高效率高保真度存储提供了实验基础。     

Effect of cavity length detuning on the output characteristics for the middle infrared FEL oscillator of FELiChEM

FELiChEM is an infrared free electron laser(FEL) facility currently under construction, which consists of two oscillators generating middle-infrared and far-infrared laser covering the spectral range of 2.5–200 μm. In this paper, we numerically study the output characteristics of the middle-infrared oscillator with accurate cavity length detuning. Emphasis is put on the temporal structure of the micropulse and the corresponding spectral bandwidth.Taking the radiation wavelengths of 50 μm and 5 μm as examples, we show that the output pulse duration can be tuned in the range of 1–6 ps with corresponding bandwidth of 13%–0.2% by adjusting the cavity length detuning.In addition, a special discussion on the comb structure is presented, and it is indicated that the comb structure may arise in the output optical pulse when the normalized slippage length is much smaller than unity. This work has reference value for the operation of FELiChEM and other FEL oscillators.     

Cavity linewidth narrowing with dark-state polaritons

We present a quantum-theoretical treatment of cavity linewidth narrowing with intracavity electromagnetically induced transparency(EIT). By means of intracavity EIT, the photons in the cavity are in the form of cavity polaritons:bright-state polariton and dark-state polariton. Strong coupling of the bright-state polariton to the excited state induces an effect known as vacuum Rabi splitting, whereas the dark-state polariton decoupled from the excited state induces a narrow cavity transmission window. Our analysis would provide a quantum theory of linewidth narrowing with a quantum field pulse.     

通气空泡尾部气泡流仿真和特性分析

基于欧拉-欧拉双流体模型对通气空泡尾部气泡流进行数值仿真, 并采用基于多尺寸分组模型的总体平衡方法预估气泡尺寸分布. 应用改进后湍流耗散系数计算模型, 考虑了气泡体积含量对在湍流作用下气泡扩散现象的影响. 基于上述模型对两种试验工况下流场进行了数值仿真.结果表明模型对空泡尾部回流区特性进行了准确预示, 在回流区高湍流度作用下气泡迅速破碎成小气泡. 并进一步得到试验体尾流区空泡体积分数和速度分布. 尾流区水流速度分布保持了流体经过非流线型对称体时产生的尾流分布规律. 仿真结果与试验数据相一致, 模型适用性得到验证.      

Bunching and Antibunching in Cavity QED

We study the statistics of the emitted filed from Rydberg atom confined inside a microcavity and interacting with a pump laser in the strong coupling regime. We explore the manifestation of the antibunching in connection with the internal system parameters.