CPT原子频标实验研究

介绍了相干布居囚禁（CPT）原子频标的小型、低功耗物理系统,并应用它开展实现了CPT原子频标的激光锁定、微波锁定方案的实验室研究.通过采用电流负反馈将激光频率锁定在原子对激光的吸收峰上,电压负反馈将微波频率锁定在电磁感应透明共振峰上,用该物理系统实现了闭环锁定的实验室桌面CPT频标实验系统.对该实验系统的频率稳定度测量获得200 s内优于5×10^-11τ^-1/2的结果. 关键词： CPT原子频标 频率稳定度 激光稳频     

Phase and spectral properties of optically injected semiconductor lasers

The main control parameters of a single mode semiconductor laser submitted to an injected external signal are the power and the frequency of the injected signal. Following their magnitude, many phenomena can be observed such as phase locking, frequency locking, frequency generation, push-pull effects, hysteresis phenomena and chaos,... We show here that the spectral signature of the slave laser enables a better understanding of the the nonlinear interaction between the two competing sources: the spontaneous emission and the external field for which spectra are equally amplified through the active medium. This amplification is then strongly dependent on their coherency. We describe the role of the injected laser as a filter and an amplifier. It follows that the laser can be used to process information in ways that are not yet completely exploited. To cite this article: S. Blin et al., C. R. Physique 4 (2003).     

Enhanced locking region in injection-locked two-section lasers

In this Letter, we investigate the criteria for achieving an enhanced stable locking region in the parameter space of injected field E_inj and frequency detuning ω in two-section semiconductor lasers subject to optical injection. Using the rate equations, a stability analysis is performed and the conditions for an enhanced locking region are deduced from the requirement for the average linewidth enhancement factor appearing in the locking-bandwidth equation to be close to zero. We calculate a stability map for an injection-locked two-section laser with an almost-symmetrical locking region that is greatly enhanced compared to a single-section injection-locked laser with identical material and control parameters.     

Alignment locking to suspended Fabry-Perot cavity

In this paper we report on the alignment locking of an in vacuum 77 m long suspended mirror Fabry-Perot cavity. Lock was achieved by mode-matching a 500 mW Nd:YAG NPRO onto a pre-mode cleaner, the output of which was then mode-matched to the suspended cavity. The longitudinal locking was achieved by feeding back to the laser frequency actuator to follow the cavity resonance. Subsequent implementation of a hybrid auto-alignment system enhanced the stability of the circulating power inside the cavity. Preliminary results are presented.     

Interferometric, modulation-free laser stabilization

We demonstrate novel modulation-free frequency locking of a diode laser, utilizing a simple Sagnac interferometer to create an error signal from saturated-absorption spectroscopy. The interference condition at the output of the Sagnac is strongly affected by the sharp dispersion feature near an atomic resonance. Slight misalignment of the interferometer and subsequent spatially selective, or tilt, detection allows this phase change to be converted into an error signal. Tilt locking has significant advantages over previously described methods, as it requires only a small number of low-cost optical components and a detector. In addition, the system has the potential to be constructed as a plug-and-play fiber-coupled monolithic device to provide submegahertz stability for lasers in the commercial market.     

Selective injection locking of a multi-mode semiconductor laser to a multi-frequency reference beam

Injection locking is a well known and commonly used method for coherent light amplification. Usually injection locking is obtained on a single-mode laser injected by a single-frequency seeding beam. In this work we show that selective injection locking of a single-frequency may also be achieved on a multi-mode semiconductor laser injected by a multi-frequency seeding beam, if the slave laser provides sufficient frequency filtering. This selective injection locking condition depends critically on the frequency detuning between the free-running slave emission frequency and each injected frequency component. Stable selective injection locking to a set of three seeding components separated by 1.2 GHz is obtained. This system provides an amplification up to 37 dB of each component. This result suggests that, using distinct slave lasers for each frequency line, a set of mutually coherent high-power radiation modes can be tuned in the GHz frequency domain.     

Bragg型声光双稳系统的调制效应

从理论上分析了Bragg型声光双稳系统的线性稳定性及调制效应.由系统的动力学方程、稳态方程出发,给出了出现双稳态的参数范围,并计算出稳区与非稳区的边界.对输入光作简谐调制时,预言了稳区输出光的共振效应和共振峰的偏移以及非稳区的频率锁定等现象.     

Injection locking of a diode laser locked to a Zeeman frequency stabilized laser oscillator

We describe the design and performance of an injection-locked diode laser locked to a stabilized, single frequency, unmodulated diode laser. The master oscillator is a grating-tuned, external cavity diode laser which is stabilized on a Doppler free alkali metal resonance transition frequency via Zeeman locking. The master oscillator frequency is shifted by an acousto-optic modulator, which provides optical isolation of the master oscillator laser while tuning of the acousto-optic modulation frequency can also provide frequency offset tuning. The slave laser is a free running diode which is injection-locked by a small fraction of the frequency shifted master oscillator light. Good long- and short-time frequency stability are observed for both the Zeeman-locked master oscillator and the injection-locked slave laser.     

High power resonant tracking amplifier using admittance locking.

A high power resonance tracking ultrasonic amplifier is described. The amplifier is a class D type inverter, configured as a half-bridge in which the output MOSFETs are driven into saturation when on. The resonance tracking system makes use of a new method of frequency locking; admittance locking is used to track the optimum power conversion frequency for the transducer. This new arrangement offers some advantages over phase locking and motional feedback methods. The system is capable of delivering up to 3 kW at up to 25 kHz in resonance tracking operation.     

平坦宽带混沌激光的产生及同步

利用光纤环长外腔光反馈半导体激光器产生了频谱平坦的宽带混沌激光,其对应的激光频谱可有效地隐藏外腔的谐振频率,增加了系统的保密性.通过单向耦合方式,将产生的混沌激光注入到另一个参数相近的半导体激光器中,实现了平坦宽带混沌同步输出,两同步激光器输出的相关系数达到084.同时实验研究了注入强度和主从激光器的频率失谐对同步质量的影响,结果表明在强光注入锁定下,在很大频率失谐范围内均可实现同步,而且注入强度越大,主从激光器输出的相关系数越大,维持混沌同步所允许的频率失谐范围越大. 关键词： 混沌同步 单向光纤环 光反馈 半导体激光器     

Mode locking in quantum optics

Mode locking phenomena in acoustics and in laser physics are discussed and are shown to share a feature of the forced oscillator: Oscillation takes place at the forcing frequency (or frequencies). The phenomena differ from simple forced oscillations in that they involve sustained oscillators (e.g., clocks, lasers) whose sustaining sources compete against the forcing signals in the choice of oscillation frequency. The locking phenomena are compared to second-order phase transitions in ferromagnetism and superconductivity where corresponding competition occurs between disordering thermal fluctuations and ordering correlations which reduce system energy.     

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。     

布拉格型声光双稳系统对弱信号的放大作用研究

在分岔点附近，通过对描述布拉格（Ｂｒａｇｇ）型声光双稳系统的差分－微分方程进行线性稳定性分析，得到了系统对小信号放大时的共振频率，给出了放大倍数的表达式。然后通过数值计算模拟出系统对小信号的放大过程，结果与理论分析相符     

PARAMETRIC STABILIZATION OF A GYROSCOPIC SYSTEM

This paper studies the stabilization of a gyroscopic system using parametric stabilization near a combination resonance. The gyroscopic system is near its primary instability, i.e., the bifurcation parameter is such that the system possesses a double zero eigenvalue. The stability of the system is studied for the linear Hamiltonian system, the damped linear system, the forced linear Hamiltonian system, and finally the damped and forced linear system. The addition of the periodic excitation near the critical combination resonance provides the system with an extended stability region when the excitation frequency is slightly above the combination resonance. A non-linear numerical example shows that these results may persist for the non-linear problem. The results of this work, are then discussed in relation to an example gyroscopic problem, a rotating shaft with periodically perturbed rotation rate.     

Dynamics of microcantilever integrated with geometric nonlinearity for stable and broadband nonlinear atomic force microscopy

We explore the use of a nonlinear cantilever system integrating geometric nonlinearity for AFM imaging, in contrast from the traditional linear cantilever system. The intrinsically nonlinear AFM cantilever system exhibits broadband resonance over a bandwidth several times of its linear resonant frequency and possesses an intrinsic stability that virtually eliminates the instability induced by the tip–sample interactions involved in a linear AFM system, thus the artifact of image contrast reversal. The ability to realize broadband operation may extend the application of AFM to spectral analysis of tip–sample interactions across a broad frequency range at the nanoscale.     

相干光注入半导体激光器锁定过程的稳定性和到达混沌态的各种不稳定现象

本文从半经典理论出发,导出半导体激光器相干光注入锁定过程的基本方程组,讨论了静态解的多支性及其稳定性,稳态调制特性及其稳定性,锁定区内外各种不稳定现象及其在光注入条件下参数平面上的分布,发现锁定区内不稳定区中部存在一混沌区,而在靠近稳定区下边界则存在一自脉动区,混沌区与自脉动区之间是其过渡区;发现到达混沌态可通过自脉动分岔(2^p型和非2^p型)、拍频自调制,以及其混合型等新的路径。 关键词：     

Spatial symmetry breaking and coexistence of attractors in a nonlinear ring cavity

We consider a passive optical system consisting of a ring cavity and a homogeneously broadened two-level medium. We find that a spatial modulation of the input beam imposes processes of competition between the external modulation frequency and the internal space frequencies which emerge from modulation instabilities. This leads to symmetry breaking phenomena when both the amplitude and the wavelength of the modulation are increased and results in the coexistence of periodic attractors. We numerically analyze the corresponding bifurcations and find that they can be explained by a generalization of the concept of cooperative frequency locking although the bifurcating attractors are periodic and are not related to linear resonator modes.     

A simple heterodyne frequency offset locking system for pulsed lasers

As a new approach the heterodyne frequency offset locking system which is applicable to a broad range of pulsed lasers is described. A 100 MHz wide-band and all-digital frequency discriminating technique is presented and an offset locking loop in which the frequency discriminator works accordingly is designed. The result of the experiment on offset locking between a CW CO₂ laser and an electro-optically Q-switched CO₂ laser with an optical pulse width 300 ns and its repetition rate 20 kHz showed that the beat frequency stability was kept within ±2 MHz.     

具有固有频率涨落的记忆阻尼线性系统的随机共振

研究了在内噪声、外噪声(固有频率涨落噪声)及周期激励信号共同作用下具有指数型记忆阻尼的广义Langevin方程的共振行为.首先将其转化为等价的三维马尔可夫线性系统,再利用Shapiro-Loginov公式和Laplace变换导出系统响应一阶矩和稳态响应振幅的解析表达式.研究发现,当系统参数满足Routh-Hurwitz稳定条件时,稳态响应振幅随周期激励信号频率、记忆阻尼及外噪声参数的变化存在"真正"随机共振、传统随机共振和广义随机共振,且随机共振随着系统记忆时间的增加而减弱.数值模拟计算结果表明系统响应功率谱与理论结果相符.     

低分析频率压缩光的实验制备

基于PPKTP晶体的阈值以下光学参量振荡(OPO)过程,制备了共振于铷原子D1线795 nm的压缩真空态光场,研究了分析频率处于千赫兹范围的主要噪声来源,特别是795 nm激光及其二次谐波397.5 nm激光在晶体内吸收引起的非线性损耗增加和系统热不稳定的问题(397.5 nm激光处于PPKTP晶体透光范围边缘,具有高于其他波长数倍的吸收系数).以795 nm和1064 nm为例,分析了非线性损耗及晶体内热效应对压缩度的影响.受限于以上因素,795 nm压缩光很难得到1064 nm波段同样的压缩度.探测系统中的噪声耦合则限制了压缩频带.实验上对分析频率为千赫兹的经典噪声进行了有效控制,通过使用真空注入的OPO、垂直偏振及反向传输的腔长锁定光、低噪声的平衡零拍探测器、高稳定度的实验系统及量子噪声锁定等方法,最终在2.6—100 kHz的分析频段得到了约2.8 dB的795 nm压缩真空.该压缩光可用作磁场测量系统的探测光以提高测量灵敏度.