Dynamical Casimir effect in superradiant light scattering by Bose–Einstein condensate in an optomechanical cavity

We investigate the effects of dynamical Casimir effect in superradiant light scattering by Bose-Einstein condensate in an optomechanical cavity. The system is studied using both classical and quantized mirror motions. The cavity frequency is harmonically modulated in time for both the cases. The main quantity of interest is the number of intracavity scattered photons. The system has been investigated under the weak and strong modulations. It has been observed that the amplitude of the scattered photons is more for the classical mirror motion than the quantized mirror motion. Also, initially, the amplitude of scattered photons is high for lower modulation amplitude than higher modulation amplitude. We also found that the behavior of the plots are similar under strong and weak modulations for the quantized mirror motion.     

Experimental Study of Double XeCl Laser with a Phase-conjugate Stimulated Scattering Cavity

SupportedbytheNationalNatureScienceFoundationofChina.1.Intr0ducti0nExcimcrlasersareonekindofthemostefficientsourcesofUVcoherentlight.Theyareusedinmanyficldssuchasn2atcrialpr0ccssing[lJ,photolitography['J,laserfusion[3Jetal..Inmany0ftheseapplicationstheshort-x`,avelcngthexcimerlaserswith1aserbeamsofhighqua1ityarenecessary.Mostoftheexci113crlasersi1regcncra11yfedbydischargecircuitswhichpumpthegasvol-umebutcausedischargeinstabiliticsinthedischargevolume['1j.Thislastphenomenonisduetothepresen…     

Slow light with cavity electromagnetically induced transparency

We report an experimental observation of slow light propagation in cold Rb atoms exhibiting cavity electromagnetically induced transparency (EIT). The steep slope of the atomic dispersion manifested by EIT reduces the light group velocity. The cavity filtering and feedback further contribute to the slowdown and delay of the light pulse propagation. A combination of the cavity and the EIT atomic system significantly improves the performance of the slow light propagation. A propagation time delay of approximately 200 ns was observed in the cavity and Rb EIT system, which is approximately 70 times greater than the time delay calculated for the light pulse propagation through the same Rb EIT system without the cavity.     

Identification of quantum cross correlations between light and an atom scattered in the field of a standing wave

To identify quantum cross correlations between a two-level atom and a cavity mode, the scattering of the atom on a standing light wave has been considered. It has been shown that, under coherent scattering conditions, a strong effect distinguishing the correlated state of the system from an independent state is observed.     

掺Yb双包层光纤激光器的时域特性和光谱特性研究

实验观测了掺Yb3+双包层光纤激光器的时域特性和光谱特性. 研究了抽运功率、腔损耗对激光器工作特性的影响. 研究发现, 利用单镜腔结构的光纤激光器, 可产生自脉动、受激布里渊散射和受激喇曼散射等非线性效应; 而采用双镜腔结构可有效抑制自脉动特性, 提高激光器工作的稳定性, 并对实验现象进行了定性的分析.     

Steady-State Orbitron Emissions

The Orbitron maser has been operated at a pressure of 2 × 10-6 in the steady state. Electrons are supplied to the device by an oxide-coated tungsten cathode placed inside the cylindrical cavity. The plasma-free emission corresponded to harmonically related steady-state narrow lines. The fundamental (lowest frequency) line corresponds to a resonance in the cavity system, which could be observed with a grid-dip meter.     

非线性波导腔耦合特性研究

对一种非线性波导耦合腔进行了理论和实验研究。研究表明,该系统的透过率随入射光强变化。对于不同的初始偏置、耦合区长度和入射功率系统具有微分放大、限幅、反常耦合和双稳运行等不同的响应。     

The Design and Simulation of a Cooling System of High Current 4-rod RFQ Cavity

To develop a high current neutron generator, preliminary studies on a high current, high duty factor 4-rod RFQ accelerator has been carried out in the Institute of Heavy Ion Physics,Peking University. This paper discusses the design of a cooling system of the RFQ cavity. Finite element program ANSYS was used to analyze the cooling system. The power density was simulated by MAFIA and used as the boundary condition of ANSYS. Due to the different meshing methods between MAFIA and ANSYS, a program was written to transfer the result of MAFIA to ANSYS. Then a thermal analysis model of RFQ cavity was built by using ANSYS. The design of the cooling system was analyzed and checked by using this model, and then the structure of cooling system is determined. Simulation results showed that the design of the cooling system makes RFQ accelerator working at proper temperature and long time steadily.     

Effect of a terahertz cavity on the conductivity of short-period GaAs/AlAs superlattices

The miniband conductivity in short-period GaAs/AlAs superlattices with a terahertz cavity has been studied. A stepwise decrease in the current caused by the formation of the electrical domains has been observed in current–voltage characteristics at a certain threshold voltage. It has been found that this threshold voltage changes considerably under the variation of the cavity parameters. The shift of the threshold has been explained by the excitation of high-amplitude oscillations in the cavity.     

Phase-locking observed among high-order lateral modes of a broad-stripe diode array inside an external cavity

For a laser diode array (LDA) positioned in an external cavity of a certain length, a very strong inter-emitter coupling can be established between the off-axis lateral modes of the broad-stripe emitters. Under these circumstances, the phase-locked operation of the LDA due to couplings between off-axis modes of emitters has been observed, for the first time to our knowledge. The observations suggest that phase locking of a broad-stripe LDA can be achieved among different emitter lateral modes by selecting different cavity lengths.     

Transient response of an electrically addressable nonlinear bistable optical device

A study has been made of the transient response of a Fabry-Perot cavity exhibiting bistability of the optical output with applied voltage. In this system the electro-optic and optical nonlinear effects act cooperatively to produce the switch, and the transient response was shown to have characteristics associated with both mechanisms. The switch was found to be composed of three distinct regions, a purely electro-optic part, followed by a slow change in the cavity intensity brought about by the electro-optic and nonlinear effects, with a final fast switch up to the high transmission state. The relative magnitude of the time duration of regions 1 and 2 was found to be dependent upon the applied voltage, initial dc biasing and optical input power. In particular, critical slowing down was evident in region 2 of the switch for values of applied voltage close to the critical value. In this case region 2 was the dominant part of the switching time. Overdriving the system resulted in the time duration of region 2 decreasing and region 1 becoming more dominant. Qualitative agreement was achieved between the experimental results and theoretical predictions of the transient response of a cavity undergoing a slow change in some external parameter.     

Discrete photodetection of quantum jumps on the V configuration of atomic levels

A theory of the discrete photodetection of quantum jumps on the V configuration of atomic levels has been developed. A three-level source atom is placed in a cavity excited by a resonance fluorescence field. The cavity is tuned to exact resonance with an atomic transition. The cavity mode state is tested by a flux of unexcited (at the entrance) probe atoms passing through the cavity. The energy states of the outgoing probe atoms are detected by ionization chambers, which are assumed ideal. This a posteriori statistical information is indirectly related to the numerical characteristics of a measured quantum system consisting of the source atom and cavity mode. The “tuning” conditions for a discrete photodetector, i.e., the rules for choosing the parameters and durations of the interactions of the cavity mode with the probe and source atoms, intensities of the pump and probe fields that are necessary for observing quantum jumps from the “bright” state to the “dark” one and vice versa, have been determined. A two-state model that describes the dynamics of a quantum jump has been analyzed. The formulas have been obtained for the observable characteristics of quantum jumps: the mean residence time of the quantum system in quasistationary states (durations of the bright and dark periods), probabilities of quantum jumps, mean excitation levels of the quantized cavity mode, etc.     

Dual squeezed states

Collective operators corresponding to two different algebras have been introduced for a simple system consisting of a single two-level atom and a high-quality cavity mode. The generators of the first algebra satisfy boson commutation relations, whereas the generators of the second algebra have been obtained by polynomial deformation of su(2) algebra. It has been shown that dual squeezed states identified using the considered commutation relations can be observed in the system placed in an entangled bath with quantum correlations.     

一种中红外腔增强甲醛检测系统的研制

介绍了研制的一种基于共轴锁模腔增强吸收光谱技术的中红外甲醛气体检测系统。系统采用了发射中心波长为3.6 μm的带间级联激光器为光源,以高精度F-P谐振腔作为气体反应池,通过激光在谐振腔内的多次反射极大地提高了有效吸收路径。为了实现甲醛检测,利用Pound-Drever-Hall（PDH）技术将激光频率和腔谐振频率锁定至波长为3 599.08 nm的甲醛吸收峰上。实验发现,谐振腔腔长容易受到外界环境的影响产生变化,导致系统失去锁定,产生测量误差;为了抑制这一现象,提高系统的准确性和抗干扰性,采用了动态PDH锁定技术,通过低频锯齿波信号对腔长进行小范围内的周期性调制,使得腔谐振频率在目标气体吸收峰附近缓慢来回变化;通过选择合适的扫描范围使得在扫描过程中激光与谐振腔保持频率锁定。系统通过光电探测器采集谐振腔透射光强信号,通过对腔透射信号进行拟合计算来确定甲醛浓度。为了验证检测系统的有效性、评估系统的性能,采用质量流量计配备了6种不同浓度的甲醛气体样品并开展了甲醛吸收光谱测量实验、系统标定实验和稳定性实验。实验结果显示,在0～10 mL·L-1范围内,腔透射信号拟合值与甲醛浓度之间呈现出良好的线性关系;通过Allan方差分析得到当积分时间为1 s时系统检测下限为52.8 nL·L-1,积分时间为14 s时检测下限可以降至3.3 nL·L-1。此外,通过增加谐振腔的腔镜反射率和腔长可以提高有效吸收路径,进一步降低检测下限。该系统灵敏度高、响应速度快,具有较好的抗干扰性和长期稳定性,在痕量甲醛检测方面具有广阔的应用前景。     

Transient response in absorptive bistability

Measurements of transient response are described for a system composed of multiple beams of atomic sodium passing through a high-finesse optical cavity. For switching from zero to incident laser intensities above the upper turning point of the steady-state hysteresis cycle, a delay in excess of the empty cavity filling time is observed for the time taken to reach steady state. For switching of the incident laser intensity from zero to above the upper turning point, this delay increases to up to 12 times the empty cavity filling time. The results are in qualitative agreement with earlier theoretical work based upon the mean-field theory for plane waves in absorptive bistability.     

Detection and Quantitation Of Several Atomic Species By Intra-cavity Quenching Of Laser Emission

Until recently laser research has been the province of the physicist wherein lasers have been utilized extensively as sources of coherent, highly monochromatic energy. The thrust of this research has been to employ the organic solution laser output as an analytical signal from which information about a particular system may be extracted. Preliminary investigations in this laboratory showed that a great number of variables are active in the achievement of lasing from an organic solution. More significantly, concurrent work in this laboratory produced some anomalous results which were subsequently attributed to a cavity defect. This suggested that small energy losses at discrete wavelengths within the resonant cavity of an organic solution laser could result in quenching of broad band laser emission at those specific wavelengths. These considerations led to investigations in which atoms and mlecules were purposefully introduced into the resonant cavity of an organic solution laser.¹ A search of the literature revealed that investigators at The National Bureau of Standards had previously observed this phenomenon and had reported on the intra-cavity absorption of a pulsed rhodamine 6G laser emission by sodium vapor.² In a follow-up paper Keller and co-workers demonstrated the enhancement of absorption for Eu(NO₃)₃) when placed within the cavity of a rhodamine 6G laser. Concurrently absorption was observed from Ba and Sr in an air-acetylene flame within a dye laser cavity by, Thrash et al.⁴ Hansch and co-workers⁵ duplicated the intra-cavity absorption experiment with iodine vapor and compared the sensitivity of this result with measurements obtained from conventional absorption techniques. At about the same time Latz, Wyles, and Green¹ reported data which dennnstrated that the extent of intra-cavity absorption for nitrogen dioxide was linearly related to its concentration. Investigation into the use of a laminar flow burner with an air-acetylene flame within a dye laser cavity showed part per billion (ppb) detection limits for sodium as well as the detection of barium and mercury. The completion of these intracavity absorption studies in the visible region of the spectrum yielded the results which are reported here as well as quantitative intyacavity absorption data for Eu⁺³. In an independent study Konjevic also reported detection of sodium by intra-cavity absorption from an airnatural gas flame⁶.     

利用腔场与可移动镜子的作用制备两种非经典态

描述了在腔场与可移动镜子相互作用系统中,适当选择作用时间,可以制备单模腔场与镜子的纠缠态,或腔场的薛定谔猫态;通过调节腔场的长度、圆频率,以及镜子的质量、振动频率等宏观物理量,可以获得不同的量子态.     

Cavity-linewidth narrowing by means of electromagnetically induced transparency

Cavity-linewidth narrowing in a ring cavity that is due to the high dispersion and reduced absorption produced by electromagnetically induced transparency (EIT) in rubidium-atom vapor has been experimentally observed. The cavity linewidth with rubidium atoms under EIT conditions can be significantly narrowed. Cavity-linewidth narrowing was measured as a function of coupling beam power.     

直线变压器驱动源模块输出电流上升时间调节

针对磁驱动等熵压缩实验对加载电流波形的特殊需求,基于改造后的1MA直线变压器驱动源(LTD)原理性模块,开展了输出电流上升时间调节实验研究。48只开关分为4组,由4根高压电缆引入触发脉冲分别触发,共进行了三组不同电缆长度组合的触发放电实验。结果表明:在±32kV充电电压下,输出电流上升时间(0~100%)可由301.2ns增加至436.0ns,相应的输出电流幅度由294.0kA下降至210.2kA。实验还采用光纤探针阵列测试系统同时对其中40只多间隙气体开关的放电发光过程进行了诊断,获得了相应开关的闭合导通起始时间。基于实验参数,利用PSpice电路模型进行了校验,并对早期触发的支路组对后续触发支路组的影响进行了分析。实验初步验证了LTD模块内部子块通过分时放电实现输出波形调节的能力。     

Demonstration of a tunable-bandwidth white-light interferometer using anomalous dispersion in atomic vapor

Recently, the design of a white-light cavity has been proposed using negative dispersion in an intracavity medium to make the cavity resonate over a large range of frequencies and still maintain a high cavity buildup. This Letter presents the first demonstration of this effect in a free-space cavity. The negative dispersion of the intracavity medium is caused by bifrequency Raman gain in an atomic vapor cell. A significantly broad cavity response over a bandwidth greater than 20 MHz has been observed. A key application of this device would be in enhancing the sensitivity-bandwidth product of the next generation gravitational wave detectors that make use of the so-called signal-recycling mirror.