涡旋光束在双拉盖尔-高斯旋转腔中的非互易传输

通过构造两个线性耦合的拉盖尔-高斯旋转腔系统,实现携带轨道角动量的涡旋光束的非互易传输现象.系统中,两个拉盖尔-高斯旋转腔模通过扭力与中间的旋转镜耦合,同时两个涡旋腔场通过光纤直接耦合起来.两个强光场分别驱动不同的腔模,并利用一个弱探测场从系统一侧入射,从而对该系统两个传播方向的光响应特性进行研究.利用该系统哈密顿量和海森伯-郎之万方程,结合输入-输出关系可得到系统的输出光谱.结果表明此系统中的涡旋光束的非互易性来源于光旋转相互作用以及涡旋腔场相互作用之间的量子干涉效应.因此,可以通过调节非互易相位差来对系统的非互易传输进行调制.此外,两个涡旋光束所携带的拓扑荷比值会显著影响传输特性;在适当的拓扑荷比值下,该系统可以实现涡旋光束的单向传输.本研究成果有望用于实现理想的涡旋光隔离器.     

厄米-高斯模与拉盖尔-高斯模的图像比较

简要地叙述了厄米-高斯模与拉盖尔-高斯模的一些理论,画出了具有代表性的厄米-高斯模与拉盖尔-高斯模在z=0平面的三维图像。为了了解厄米-高斯模与拉盖尔-高斯模的各种模态的关系,分别画出了它们的模态从(0,0)到(2,2)的强度等高线,并从模阶数与峰值、峰值的变化、延伸面积和对称性得到了它们各自的特性,然后进行对比得到它们之间的相同点和不同点。另外通过图像和公式说明了厄米-高斯与拉盖尔-高斯最低阶模(0,0)是一致的,即高斯模。对比了它们之间的电(磁)场和平均坡印廷矢量,不同点与模态有很大关系。画出横截面中振幅强度随传输距离增加而变化的图像,从中得到了束宽和峰值强度与传输距离之间的关系。     

水下拉盖尔-高斯涡旋光束及其叠加态传输特性

通过实验研究了拉盖尔-高斯涡旋光束及其叠加态在水下湍流中的传输特性,充分考虑了不同温度差和盐度差的水流扩散产生的湍流对4种光束（高斯光束,阶数为0、拓扑荷数为6的拉盖尔-高斯涡旋光束,阶数为1、拓扑荷数为2与阶数为0、拓扑荷数为6的拉盖尔-高斯涡旋光叠加,阶数为1、拓扑荷数为2与阶数为0、拓扑荷数为10的拉盖尔-高斯涡旋光叠加）传输的影响,并对4种光束的漂移方差和闪烁指数进行深入讨论与分析。实验结果表明：随着湍流强度的增大,4种光束的漂移方差和闪烁指数都增大,相比其他3种光束,拉盖尔-高斯涡旋光束的漂移方差和闪烁指数较小;在较弱的湍流强度下,两种涡旋光叠加态的漂移方差和闪烁指数与拉盖尔-高斯涡旋光束相近。     

光纤激光器反馈耦合损耗分析

将双包层光纤基模LP01模近似表示为拉盖尔-高斯光束的线性叠加,前六阶的拉盖尔-高斯光束包含了LP01模能量的99.99％.利用拉盖尔-高斯光束的传输特性计算了腔镜分别为球面镜和透镜加平面反射镜时的反馈耦合损耗.结果表明,腔镜为球面镜时,只有当球面镜和到达球面镜光束的曲率半径匹配时才能获得最小的耦合损耗,特别是当平面镜紧贴光纤端面时,耦合损耗为0;当腔镜为透镜加平面反射镜时,将平面镜放置在透镜焦平面时获得最小反馈耦合损耗为0.25％.     

糖类同分异构体的太赫兹吸收峰形成机理研究

建立了一种新型拉盖尔-高斯幂指数相位涡旋光束(PEPVB)理论模型,并基于广义柯林斯公式建立了拉盖尔-高斯PEPVB在傍轴近似下的传输理论模型。采用MATLAB数值计算软件仿真了拉盖尔-高斯PEPVB的自由空间传输特性和聚焦特性与径向阶数、拓扑荷数、幂指数和传输距离的关系。研究结果表明拉盖尔-高斯PEPVB及其传输特性不仅与幂指数和拓扑荷数有关,还与拉盖尔-高斯多项式的径向阶数有关,且在传输过程中光束能量沿着环形旋转聚集。这为光学操控微粒沿弯曲路径移动并避开障碍物打下了基础,对促进新型光场调控的理论及应用研究具有重要的意义。     

球形粒子在聚焦拉盖尔-高斯光束中的散射特性研究

研究了球形粒子在聚焦拉盖尔-高斯光束中的散射特性. 根据广义Mie理论, 推导出球形粒子在聚焦拉盖尔-高斯光束中散射系数的解析公式. 针对光束的电场分布及粒子散射强度进行了数值仿真, 讨论了散射强度随散射角、散射球粒子半径和拓扑荷的变化特性, 并通过散射系数解释了散射强度分布的振荡现象. 结果表明, 在聚焦拉盖尔-高斯光束照射下, 球形粒子的后向散射强度随着粒子半径的增大而逐渐增大; 后向散射强度开始增大时对应的粒子半径与拓扑荷有关. 通过与高斯光束的对比, 可以看出球形粒子在聚焦拉盖尔-高斯光束中散射特性的差异, 使其在粒径测量、光通信和大气后向散射探测等方面具有潜在应用价值.     

螺旋轴棱锥的光束传输特性

 分析了螺旋轴棱锥的结构和光传输特性,基于衍射积分理论研究了发散球面波和拉盖尔-高斯光束经螺旋轴棱锥后的传输过程。研究表明,发散球面波经过螺旋轴棱锥后产生贝塞尔光束,其阶数与拓扑电荷数相同,但中心光斑（空心光斑）半径随传输距离的增加而变大;拉盖尔-高斯光束入射后同样产生贝塞尔光束,但其阶数变为拉盖尔-高斯光束和螺旋轴棱锥的拓扑电荷数之和,出射光束的拓扑电荷数与阶数相等。     

大模场一维高阶厄米-高斯激光束产生

厄米-高斯光束在诸多前沿科学领域都有着重要的应用.不同于目前普遍采用的晶体端面离轴泵浦方式,本文提出了一种利用板条激光器产生厄米-高斯激光束的方法.采用半导体激光阵列大面正交泵浦板条激光介质,具有大模场特性.根据预先设计的谐振腔模场,在板条厚度和宽度方向分别采用尺寸可调的光阑限模.由于高阶模式对谐振腔腔镜不对准的灵敏度弱于低阶模式,可通过耦合输出镜倾斜量的控制,实现不同阶数模式腔内损耗的差异化调控,从而产生各阶次的高纯度厄米-高斯光束.利用Nd:YAG板条激光器,获得了0—9阶一维厄米-高斯光束,其光强分布与理论值的相关系数ρ高于0.95,光束质量因子M²与理论值符合良好.最高阶HG₀₉模式的输出功率为244 mW.在此基础上,进一步利用柱透镜对组成的像散模式转换器,实现了各阶厄米-高斯光束向对应拉盖尔-高斯光束的转换.结合板条放大器结构,基于本方案产生的厄米-高斯光束具备功率定标放大的前景.     

厄米-高斯模和拉盖尔-高斯模及它们之间的转换

介绍了厄米-高斯模和拉盖尔-高斯模的特点,基于厄米多项式与拉盖尔多项式之间的关系,给出了拉盖尔-高斯模用对角的厄米-高斯模的展开式表示,进而讨论了利用模式转换器使厄米-高斯光束转化为拉盖尔-高斯光束的方法。     

耦合腔阵列与Λ-型三能级原子非局域耦合系统中单光子的传输特性研究

讨论了理想和非理想情况下耦合腔阵列中两个最邻近的腔与Λ-型三能级原子非局域耦合系统中单光子的传输特性.运用准玻色子方法,精确地解出了开放系统中单光子的透射率.Λ-型三能级原子与耦合腔阵列非局域耦合系统具有更多的优点,如:该系统比其他系统调控光子传输特性的可调控参数更多;单光子在该系统中传输的透射谱有三个透射峰.此外,该系统还具有自身的特点,当拉比频率?取值给定之后,改变原子与其中一个腔的耦合强度时,光子的透射谱有一个透射率始终为1的定点,该点对应的光子频率为ω_c-?.在非理想情况下,系统耗散对光子的透射谱有着很大的影响.当只考虑原子耗散时,耗散使得光子透射谱的谷值增大,而峰值不变;当只考虑腔场耗散时,光子透射谱的峰值减小,而谷值不变.另外,随着腔场耗散率和腔的个数的增多,光子透射谱的峰值逐渐减小,但谷值始终不变.对比原子耗散和腔场耗散的情况可以发现,原子耗散使得光子不能被完全反射,而腔场耗散使得光子不能被完全透射.当同时考虑原子和腔场耗散时,光子透射谱谷值的大小不但会受原子耗散率大小的影响,也受腔场耗散率大小的影响,随着腔场耗散率的增大,谷值反而减小;而光子透射谱的峰值始终只受腔场耗散率大小和腔的个数的影响,与原子耗散率取值的大小无关.     

Determination of the number of atoms trapped in an optical cavity

The number of atoms trapped within the mode of an optical cavity is determined in real time by monitoring the transmission of a weak probe beam. Continuous observation of atom number is accomplished in the strong coupling regime of cavity quantum electrodynamics and functions in concert with a cooling scheme for radial atomic motion. The probe transmission exhibits sudden steps from one plateau to the next in response to the time evolution of the intracavity atom number, from N>or=3 to N=2-->1-->0 atoms, with some trapping events lasting over 1 s.     

Observation of the vacuum Rabi spectrum for one trapped atom

The transmission spectrum for one atom strongly coupled to the field of a high finesse optical resonator is observed to exhibit a clearly resolved vacuum Rabi splitting characteristic of the normal modes in the eigenvalue spectrum of the atom-cavity system. A new Raman scheme for cooling atomic motion along the cavity axis enables a complete spectrum to be recorded for an individual atom trapped within the cavity mode, in contrast to all previous measurements in cavity QED that have required averaging over 10(3)-10(5) atoms.     

等同双原子Jaynes-Cummings模型的量子特性及系统光谱

在全量子理论的背景下提出两个二能级原子分别与一单模腔场相互作用的系统模型,利用量子主方程和数值模拟计算等方法,研究该体系中腔场平均光子数、Mandel's Q因子及二阶量子相关度在非稳态时的变化规律。此外,对体系中原子及腔场中光谱结构进行了分析。结果表明:减小腔场耗散系数,增大原子间耦合系数,体系量子特性愈加明显。体系光谱呈现出Mollow三重峰结构,且原子辐射谱强度远大于腔场辐射谱强度。当原子跃迁频率与腔场跃迁频率为近共振时,Mollow峰值为三峰中最大值。此外,增大原子与腔场间耦合系数,可增大原子光谱的中峰强度;而增大腔场光谱的中峰强度,则需减小原子与腔场间耦合系数。     

Optomechanical dynamics in detuned whispering-gallery modes cavity

The dynamics of a microresonator in detuned whispering-gallery modes (WGM) cavity opto-mechanical system are investigated by the quantum Langevin equation. A WGM cavity coupling to two parallel waveguides is devised to study the transmission and reflection of this system. In single mode WGM cavity, without optomechanical coupling, both the transmission and reflection of the cavity present a Lorentzian dip and peak. When the coupling between the cavity mode and mechanical mode is considered, the transmission and reflection of the optomechanical cavity show “W” and “M” shape mode splitting. Moreover, under the action of a controlling and a probe laser, the output field at the probe frequency presents electromagnetically induced transparency (EIT)-like spectrum in the system. We give the physical origin of EIT-like and the pump-probe response for the WGM shares all the features of the Λ system in atoms. Further, due to backscattering, the two traveling waves in WGM are coupled with a rate γ. The transmission and reflection of the optomechanical cavity display three modes splitting in the spectra with optomechanical coupling between the two cavity modes and the mechanical mode.     

Cavity QED with quantized center of mass motion

We investigate the quantum fluctuations of a single atom in a weakly driven cavity, where the center of mass motion of the atom is quantized in one dimension. We present analytic results for the second order intensity correlation function g((2))(tau) and the intensity-field correlation function h(theta)(tau), for transmitted light in the weak driving field limit. We find that the coupling of the center of mass motion to the intracavity field mode can be deleterious to nonclassical effects in photon statistics and field-intensity correlations, and compare the use of trapped atoms in a cavity to atomic beams.     

Collective effects in the dynamics of driven atoms in a high-Q resonator

We study the quantum dynamics of N coherently driven two-level atoms coupled to an optical resonator. In the strong coupling regime the cavity field generated by atomic scattering interferes destructively with the pump on the atoms. This suppresses atomic excitation and even for strong driving fields prevents atomic saturation, while the stationary intracavity field amplitude is almost independent of the atom number. The magnitude of the interference effect depends on the detuning between laser and cavity field and on the relative atomic positions and is strongest for a wavelength spaced lattice of atoms placed at the antinodes of the cavity mode. In this case three dimensional intensity minima are created in the vicinity of each atom. In this regime spontaneous emission is suppressed and the dominant loss channel is cavity decay. Even for a cavity linewidth larger than the atomic natural width, one regains strong interference through the cooperative action of a sufficiently large number of atoms. These results give a new key to understand recent experiments on collective cavity cooling and may allow to implement fast tailored atom-atom interactions as well as nonperturbative particle detection with very small energy transfer.Received: 18 May 2004, Published online: 19 October 2004PACS: 32.80.Pj Optical cooling of atoms; trapping - 42.50.Pq Cavity quantum electrodynamics; micromasers - 42.50.Fx Cooperative phenomena in quantum optical systems     

3D dissipative motion of atoms in a strongly coupled driven cavity

We develop quantum models for the combined external and internal motion of atoms in a strongly coupled driven cavity mode including the transverse degrees of freedom. Using a simplified Gaussian mode function we determine the parameter regimes and prospects of 3D cooling and confinement of one or two atoms in the cavity field. Analysing the field dynamics for slow atoms traversing the cavity, we show that the spectrum of the transmitted and spontaneously scattered light contains ample information on the motional dynamics of the atom and can be nicely used to investigate the cooling properties of the system. Including several atoms in the dynamics we show how motional correlations build up by the common interaction with the cavity field. This can be looked upon as collisions at far distance and can be monitored via the transmitted field dynamics. Received 5 March 1999 and Received in final form 4 May 1999     

两原子与双模腔场喇曼相互作用(g1≠g2)的辐射谱

研究了两个有效双能级原子与双模腔场具有不同耦合常数(g₁≠g₂)时通过喇曼相互作用的辐射谱,详细讨论了双模腔场分别处于不同数态时的情形,发现其辐射谱具有如下新特点:当模1腔场处于真空态,模2腔场处于弱场中时,随着R=g₂/g₁的增加,辐射谱交替出现对称的10峰、6峰结构,与单模双原子情形相比较,更为灵敏地反映出两原子与腔场间不同的喇曼相互作用强度;当模1腔场处于真空态、模2腔场处于强场中时,0相似文献   

Transverse mode control by manipulating gain distribution in a Yb:YAG ceramic thin disk

We demonstrated that transverse mode can be controlled by manipulating gain distribution in a Yb:YAG ceramic thin disk. Several elongated higher order transverse modes of a Hermite-Gaussian beam were observed when a straight-line-shaped gain region was created by using a diode laser output from an optical fiber. An orthogonally crossing pair of straight-line-shaped gain regions created with an additional optical fiber output resulted in the generation of a doughnut-shaped Laguerre-Gaussian beam. This implies that easy and quick switching of Hermite-Gaussian and Laguerre-Gaussian beams is possible without mechanical handling.     

两模腔场谱间的量子干涉

研究了高Q腔中单个二能级原子与两模二项式光场依赖强度耦合相互作用系统的腔场谱,给出了弱初始场条件下的数值结果,讨论了两模光场之间的量子干涉对腔场谱结构的影响. 发现当两模光场的频率差Δ>g（g为原子与腔场间的耦合常数）时,两模光场间的干涉效应对谱结构没有影响,系统的腔肠谱只是两模腔肠谱的简单叠加;当Δ≤g时两模腔场谱间的干涉比较明显. 在强初始场条件下,量子干涉效应可忽略. 关键词： 腔场谱 量子干涉 两模二项式光场