平行线偏光激发CPT共振方案实验研究

目前的相干布居囚禁(CPT)原子钟和CPT磁场计中普遍采用圆偏振光方案 (σ⁺-σ⁺)实现CPT共振, 该方案对原子的利用率较低. 为了提高原子的利用率, 本文实验研究了通过平行线偏振相干双色光与⁸⁷Rb原子作用实现CPT共振的方案(lin//lin). 与σ⁺-σ⁺方案相比较, lin//lin方案消除了极化暗态, 获得更多工作原子. 在相同的实验条件下, 开展对比实验研究获得了信噪比为σ⁺-σ⁺方案2倍, 微分线型信号的中心斜率为σ⁺-σ⁺方案1.65倍的CPT共振信号. 研究结果表明该方案是实现低功耗原子钟、磁场计等设备的理想候选.     

Bright optical lattices in a longitudinal magnetic field. Experimental study of the oscillating and jumping regimes

All the bright optical lattices studied so far have been designed to obtain a circularly polarized light at the bottom of the optical potential wells. This condition minimizes the departure rate of the atoms from the fundamental adiabatic surface and permits an oscillating regime in a large range of parameters. We present here an experimental study of cesium atoms in a three-dimensional optical lattice, where the light is linearly polarized at the bottom of the potential wells. Temperature measurements and pump-probe spectroscopy give similar results for this lattice and for the conventional lin lin lattice (which have circular polarizations at the bottom of the wells) despite the fact that one lattice operates in the jumping regime and the other in the oscillating regime. We study the behaviour of the two types of lattices in a longitudinal magnetic field, with particular emphasis on the zero field and strong field regimes. The strong field situation is very simple because the eigenstates are then almost pure Zeeman substates and the adiabatic and diabatic potential surfaces are identical. The comparison between the zero-field and the high-field situations shows that the diabatic potentials are more appropriate to account for experimental observations in the novel lattice. Received: 9 October 1997 / Accepted: 6 November 1997     

Designing coupled microcavity lasers for high-Q modes with unidirectional light emission

We design coupled optical microcavities and report directional light emission from high-Q modes for a broad range of refractive indices. The system consists of a circular cavity that provides a high-Q mode in the form of a whispering gallery mode, whereas an adjacent deformed microcavity plays the role of a waveguide or collimator of the light transmitted from the circular cavity. As a result of this very simple, yet robust, concept we obtain high-Q modes with promising directional emission characteristics. No information about phase space is required, and the proposed scheme can be easily realized in experiments.     

On the unique possibility of significantly increasing the contrast of dark resonances on the D1 line of <Superscript>87</Superscript>Rb

We propose and study, theoretically and experimentally, a new scheme of excitation of a coherent population trapping resonance for the D1 line of alkali atoms with nuclear spin I = 3/2 by bichromatic linearly polarized light (lin‖lin field) under the conditions of spectral resolution of the excited state. The unique properties of this scheme result in a high contrast of dark resonance for the D1 line of ⁸⁷Rb.     

PMMA材料在线偏振和圆偏振光下的超连续光谱特性分析

飞秒激光在透明材料加工过程中会出现超连续光谱现象。在阐述超连续光谱产生的原理的基础上,为了分析PMMA材料在不同偏振光下产生的超连续光谱的阈值,设计了线偏光和圆偏光及不同能量加工PMMA材料的实验方案。利用光谱仪对产生的超连续光谱信号进行采集及处理,分析出不同能量下的线偏振(TE和TM)和圆偏振两种偏振态的超连续光谱的变化规律,并对比了相同能量下线偏振和圆偏振的超连续光谱的区别。实验中采用脉宽160 fs、中心波长为775 nm的飞秒激光,实验结果表明,同一偏振下能量越大,光谱谱宽越宽;通过对比不同能量下的光谱特性,观测出产生超连续光谱的阈值, 线偏振光的阈值为0.46 μJ,圆偏振光的阈值为0.586 μJ;对比相同能量下的线偏振和圆偏振光,线偏振的谱宽比圆偏振的宽。     

水下物体激光圆偏振成象实验及与线偏振成象的比较

采用波长532nm激光作光源,面阵CCD作探测器,利用圆偏振技术进行水下物体成象实验研究,对实验结果进行了分析并与线偏振成象技术进行了比较。结果表明无论是采用圆偏振技术还是线偏振技术都可提高水下物体成象的衬比（度）和成象距离;水体较清时圆偏振成象清晰度远远大于线偏振成象清晰度;当水体较混时,圆偏振成象清晰度大大下降和线偏振成象效果相接近。     

Study of Electromagnetic Properties of Light Baryons in the Hypercentral Approach

Light flavour baryons are studied in a non-relativistic potential model with colour Coulomb plus linear confinement potential using a simple variational method. The ground-state masses and magnetic moments of the light baryons are computed using a spin- and isospin-dependent potential. We extend our scheme to predict the transition magnetic moments of \(B_{(J^{P}={3/2}^{+})} \rightarrow B_{(J^{P}={1/2}^{+})}\gamma \) processes. We also compute the radiative decay widths and branching ratios of light baryons. A comparison of our results with those of other works and experimental data is also presented.     

Simulations of frequency-domain spectra: structure-function relationships in photosynthetic pigment-protein complexes

The theory of dissipative exciton motion in chromophore complexes is applied to develop an approximate scheme for the simulation of frequency-domain linear absorption and circular dichroism. Besides lifetime broadening of the exciton lines and the inclusion of vibrational satellites in the spectra, the computations also account for static disorder. In applying the theory to a pigment protein complex of the photosynthetic light harvesting complex LHC-II of green plants the temperature dependence of linear absorption can be well reproduced.     

Observation of large Kerr nonlinearity at low light intensities

We report an experimental observation of large Kerr nonlinearity with vanishing linear susceptibilities in coherently prepared four-level rubidium atoms. Quantum coherence and interference manifested by electromagnetically induced transparency suppress the linear susceptibilities and greatly enhance the nonlinear susceptibilities at low light intensities. The measured Kerr nonlinearity is comparable in magnitude to the linear dispersion in a simple two-level system and is several orders of magnitude greater than the Kerr nonlinearity of a conventional three-level scheme under similar conditions.     

Pump-probe spectroscopy of atoms cooled in a 3D lin lin optical lattice

We describe the pump-probe spectroscopy of atoms cooled in a 3D lin⊥lin optical lattice. Our pump-probe configuration consists of two laser fields detuned with respect to the lattice fields. This scheme allows to clearly identify in the probe transmission spectrum the Brillouin and Raman resonances, by studying their positions as functions of the angle between the pump and probe beams. We describe these resonances in detail, and compare the experimental results to the theoretical predictions. Our conclusions are supported by transport-spectroscopy measurements, which allow to distinguish between contributions to the light scattering from propagating and non-propagating atoms. Received 8 April 2002 / Received in final form 9 September 2002 Published online 12 November 2002     

一种全光纤型观测光波粒二象性的方法

提出一种结构简单、实验现象明显的光波粒二象性观测方案,本方案以波的相干叠加突出显示光的波动性,以粒子在50/50分束器的路径随机选择特性突出显示光的粒子性.以衰减强激光脉冲为光子源,在实验室获得的干涉对比度超过99%,单粒子特性超过90%.实验结果表明此方案有望在实际得到广泛应用.     

Investigation of the nonlinear CPT spectrum of ~(87)Rb and its application for large dynamic magnetic measurement

The coherent population trapping(CPT) phenomenon has found widespread application in quantum precision measurements. Various designs based on the narrow resonant spectrum corresponding to the linear Zeeman effect have been demonstrated to achieve high performance. In this article, the nonlinear Zeeman split of the CPT spectrum of ~(87)Rb in the lin||lin setup is investigated. We observe re-split phenomenon for both magnetic sensitive and magnetic insensitive CPT resonant lines at a large magnetic field. The re-split in the magnetic sensitive lines raises a practical problem to magnetometers worked in the lin||lin setup while the other one shows a good potential for applications in large magnetic field. We propose a design based on the nonlinear split of the magnetic insensitive lines and test its performance. It provides a much larger measurement range compared to the linear one, offering an option for atomic magnetometers where a large dynamic range is preferred.     

宏观可分辨量子态的产生和检测

本文利用SO(3)旋转群性质得到了非线性双折射介质模型的一个严格解.由此证明相干态进入双折射介质后将产生宏观上可分辨的量子迭加态.为检测它们所产生的干涉条纹,本文采用零拍检测方案,计算了初态为线偏振和圆偏振相干光时零拍检测器输出流的几率分布.     

Dual-frequency optical pumping for spin-polarizing a lithium atomic beam

A lithium-6 atomic beam is spin-polarized by means of optical pumping with a single-mode dye laser operating on the resonance transition. Simultaneous pumping of both hyperfine substates is achieved by frequency-splitting the laser light with an acousto-optic modulator. A polarization dependent signal, obtained by probing the optical activity of the beam with linearly polarized light, is utilized in a microprocessor-controlled laser stabilization scheme. The polarization is analyzed with a sextupole magnet and its overall value is 0.70 for an intensity of 1×10¹⁴ atms s⁻¹. By reversing the sense of circular polarization of the pumping light the atomic beam polarization is easily reversed in direction.     

Topological structure in polarization resolved conoscopic patterns for nematic liquid crystal cells

We investigate the polarization structure of coherent light, produced by a convergent light beam transmitted through nematic liquid crystal (NLC) cells with different director configurations. Employing solutions to the transmission problem for the case when plane wave propagates through an anisotropic layer, we analyze the arrangement of the topological elements, such as polarization singularities (C points with circular polarization and L lines with linear polarization), saddle points and extrema of polarization azimuth. We observe transformations of the topological structure under the variation of the incident light ellipticity and represent it by corresponding trajectories of topological elements in three-dimensional space. For the cells with uniform and non-uniform director configuration we describe the processes of creation/annihilation of C point pairs, which can be controlled precisely in the case of the cell with non-uniform director. Our experimental measurements for the homeotropically oriented NLC cells are in good agreement with the theoretical predictions.     

Opus musicum

The rotation of the plane of linearly polarized light by an optically-active medium arises from a difference between the refractive indices of the medium for left- and right-circularly polarized light. The circular birefringence is related to a circular dichroism, which is exhibited by all molecules which are not superposable on their mirror image and exist as laevo- and dextro-rotatory isomers. The circular dichroism of a dissymmetric molecule in a particular absorption region originates from an electronic transition with collinear electric and magnetic dipole moments, corresponding to the displacement of a molecular valency electron through a helical path by the absorption of radiation. The right- or left-handed form of the helical path depends upon the molecular structure, and the absolute stereochemical configuration of dissymmetric molecules may be determined by comparing their circular dichroism spectra with the calculated rotational strengths. In addition the polarization direction of an electric moment and the magnitude of a magnetic moment of an electronic transition in a dissymmetric molecule may be derived from circular dichroism measurements.     

A Monte Carlo ray tracing study of polarized light propagation in liquid foams

A Monte Carlo ray tracing scheme is used to investigate the propagation of an incident collimated beam of polarized light in liquid foams. Cellular structures like foam are expected to change the polarization characteristics due to multiple scattering events, where such changes can be used to monitor foam dynamics. A statistical model utilizing some of the recent developments in foam physics is coupled with a vector Monte Carlo scheme to compute the depolarization ratios via Stokes-Mueller formalism. For the simulations, the incident Stokes vector corresponding to horizontal linear polarization and right circular polarization are considered. It is observed that bubble size and the polydispersity parameter have a significant effect on the depolarization ratios. This is partially owing to the number of total internal reflection events in the Plateau borders. The results are discussed in terms of applicability of polarized light as a diagnostic tool for monitoring foams.     

Cold highly charged ions in a cryogenic Paul trap

Narrow optical transitions in highly charged ions (HCIs) are of particular interest for metrology and fundamental physics, exploiting the high sensitivity of HCIs to new physics. The highest sensitivity for a changing fine structure constant ever predicted for a stable atomic system is found in Ir^17?+?. However, laser spectroscopy of HCIs is hindered by the large (～ 10⁶ K) temperatures at which they are produced and trapped. An unprecedented improvement in such laser spectroscopy can be obtained when HCIs are cooled down to the mK range in a linear Paul trap. We have developed a cryogenic linear Paul trap in which HCIs will be sympathetically cooled by ⁹Be^?+? ions. Optimized optical access for laser light is provided while maintaining excellent UHV conditions. The Paul trap will be connected to an electron beam ion trap (EBIT) which is able to produce a wide range of HCIs. This EBIT will also provide the first experimental input needed for the determination of the transition energies in Ir^17?+?, enabling further laser-spectroscopic investigations of this promising HCI.     

Local control of light polarization with low-temperature fiber optics

A fiber-optic-based polarization control system that uses a backreflection measurement scheme at low temperatures has been developed. This provides a stringent test of the light polarization state at the output of the fiber, allowing for determination and control of the degree of circular polarization; i.e., it can generate linear, right, or left circular polarization with cryogenic fibers. This polarization controller is paving the way toward the control and manipulation of nuclear spins in semiconductors via the optical Overhauser effect and could be used, for example, for the purpose of quantum information processing with the large nuclear spins of GaAs.     

Vortex phase qubit: generating arbitrary, counterrotating, coherent superpositions in Bose-Einstein condensates via optical angular momentum beams

We propose a scheme for the generation of arbitrary coherent superpositions of vortex states in Bose-Einstein condensates (BEC) using the orbital-angular-momentum states of light. We devise a scheme to generate coherent superpositions of two such counterrotating states of light using well-known experimental techniques. We show that a specially designed Raman scheme allows for transfer of the optical vortex-superposition state onto an initially nonrotating BEC. This creates an arbitrary and coherent superposition of a vortex and antivortex pair in the BEC. The ideas presented here could be extended to generate entangled vortex states, design memories for the orbital-angular-momentum states of light, and perform other quantum information tasks. Applications to inertial sensing are also discussed.