用于冷原子干涉仪激光时序控制的DDS跳频系统设计与实现

为了满足冷原子干涉实验对时序控制的需求,设计并实现了一个基于LABVIEW软件的激光时序控制DDS系统,其工作过程为通过设计的LABVIEW上位机软件输入需要产生的频率和频率间隔时间,ARM芯片根据LABVIEW软件发送来的控制信息实现对射频信号芯片的控制,CPLD芯片用来控制射频信号之间的时间间隔,最后DDS芯片产生与控制信息相对应的射频信号。与目前同类装置相比,系统实现了跳频时间和频率更加精确和工作稳定性更好。经过系统的调试分析以及性能测试,DDS跳频系统能够满足原子干涉仪激光时序控制需求。通过测试DDS装置,DDS装置能够输出准确输出射频频率值,并且射频频率时间间隔能精确到微秒。DDS装置可以有效控制冷原子干涉仪的激光时序,在探询时间为120毫秒且重复率为2.2赫兹的情况下,冷原子重力仪的重力测量灵敏度达到 。     

Light-pulse atom interferometry in microgravity

We describe the operation of a light pulse interferometer using cold ⁸⁷Rb atoms in reduced gravity. Using a series of two Raman transitions induced by light pulses, we have obtained Ramsey fringes in the low gravity environment achieved during parabolic flights. With our compact apparatus, we have operated in a regime which is not accessible on ground. In the much lower gravity environment and lower vibration level of a satellite, our cold atom interferometer could measure accelerations with a sensitivity orders of magnitude better than the best ground based accelerometers and close to proven spaced-based ones.     

The Sagnac effect: 20 years of development in matter-wave interferometry

Since the first atom interferometry experiments in 1991, measurements of rotation through the Sagnac effect in open-area atom interferometers have been investigated. These studies have demonstrated very high sensitivity that can compete with state-of-the-art optical Sagnac interferometers. Since the early 2000s, these developments have been motivated by possible applications in inertial guidance and geophysics. Most matter-wave interferometers that have been investigated since then are based on two-photon Raman transitions for the manipulation of atomic wave packets. Results from the two most studied configurations, a space-domain interferometer with atomic beams and a time-domain interferometer with cold atoms, are presented and compared. Finally, the latest generation of cold atom interferometers and their preliminary results are presented.     

Comparison of two absorption imaging methods to detect cold atoms in magnetic trap

Two methods of absorption imaging to detect cold atoms in a magnetic trap are implemented for a high-precision cold atom interferometer.In the first method,a probe laser which is in resonance with a cycle transition frequency is used to evaluate the quantity and distribution of the atom sample.In the second method,the probe laser is tuned to an open transition frequency,which stimulates a few and constant number of photons per atom.This method has a shorter interaction time and results in absorption images which are not affected by the magnetic field and the light field.We make a comparison of performance between these two imaging methods in the sense of parameters such as pulse duration,light intensity,and magnetic field strength.The experimental results show that the second method is more reliable when detecting the quantity and density profiles of the atoms.These results fit well to the theoretical analysis.     

Measuring gravitational effect of superintense laser by spin-squeezed Bose—Einstein condensates interferometer

We consider an extremely intense laser, enclosed by an atom interferometer. The gravitational potential generated from the high-intensity laser is solved from the Einstein field equation under the Newtonian limit. We compute the strength of the gravitational force and study the feasibility of measuring the force by the atom interferometer. The intense laser field from the laser pulse can induce a phase change in the interferometer with Bose-Einstein condensates. We push up the sensitivity limit of the interferometer with Bose-Einstein condensates by spin-squeezing effect and determine the sensitivity gap for measuring the gravitational effect from intense laser by atom interferometer.     

Interferometry with Ca atoms

Separated field excitation of a calcium atomic beam using four traveling laser fields represents two distinct atom interferometers utilizing the internal degrees of freedom of the atoms. Phase shifts between the atomic partial waves have been realized by phase shifts of the laser wave fields, by the ac-Stark shift, and by rotation of the interferometer (Sagnac effect). One particular interferometer can be selected by interaction of the atomic waves with extra laser fields. We furthermore report on the preparation of a laser cooled and deflected calcium atomic beam that can be utilized to largely increase the sensitivity of the interferometer.     

The magnesium ramsey interferometer: Applications and prospects

In this paper it will be shown that an atom interferometer, based on the coherent splitting of the atomic wavefunction by four travelling waves (Ramsey interferometer), may be explained by a purely mechanical interpretation. As our first application of this Ramsey interferometer we have measured the phase shifts respectively optical length changes in a magnesium atomic beam caused by the acceleration of the partial atomic wave in one arm of the interferometer. This acceleration was achieved by the dipole force exerted by an off-resonant crossing laser beam which interacted with the ground state part of the wavefunction only. Further applications of this interferometer and improvements due to laser cooling will be discussed.     

Topological phase shift in a cold-atom interferometer

Matter-wave interferences in a four-pulse version of a Ramsey-Bordé atom interferometer have been utilized to study phase shifts. A topological phase shift analogous to the scalar Aharonov-Bohm effect proposed for charged-particle interferences in the presence of a pulsed electrostatic potential has been investigated. The time-dependent potential has been generated by the interaction of a laser field with an induced atomic dipole without spatial variation along the interferometer arms. The atom interferometer has been run with laser-cooled magnesium atoms stored in a magneto-optical trap.Dedicated to H. Walther on the occasion of his 60th birthday     

Measurement of the frequency modulation transfer function of a laser using a Mach–Zehnder interferometer

A technique is presented for determining the frequency modulation transfer function of a laser. The method is based on a Mach–Zehnder interferometer, with a significant difference in the optical path lengths of the two arms. A frequency-modulated laser beam incident on the interferometer produces a phase-modulated photocurrent signal with an effective modulation index that is related to the amplitude of the optical frequency modulation. Techniques for determining both the amplitude and the phase of the optical frequency modulation from the photocurrent signal are described.     

光和原子关联与量子计量

物理量的测量与单位标准的统一推动了计量学的发展.量子力学的建立,激光技术的发明以及原子与分子物理学的发展,在原理与技术上进一步刷新了计量学的研究内涵,特别是激光干涉与原子频标技术的发展,引起了计量学革命性的飞跃.基于激光干涉的引力波测量、激光陀螺仪,基于原子干涉的原子钟、原子陀螺仪等精密测量技术相继诞生,一个以量子物理为基础,探索与开拓物理量精密测量方法与技术的新的科学分支——量子计量学(Quantum Metrology)已然兴起.干涉是计量学中最常用的相位测量方法.量子干涉技术,其相位测量精度能够突破标准量子极限的限制,是量子计量学与量子测量技术的核心研究内容.本文重点介绍近几年我们在量子干涉方面所取得的新开拓与新发展,主要内容包括基于原子系综中四波混频过程的SU(1,1)型光量子关联干涉仪和基于原子系综中拉曼散射过程的光-原子混合干涉仪.     

Low noise amplification of an optically carried microwave signal: application to atom interferometry

In this paper, we report a new scheme to amplify a microwave signal carried on a laser light at λ=852 nm. The amplification is done via a semiconductor tapered amplifier and this scheme is used to drive stimulated Raman transitions in an atom interferometer. Sideband generation in the amplifier, due to self-phase and amplitude modulation, is investigated and characterized. We also demonstrate that the amplifier does not induce any significant phase-noise on the beating signal. Finally, the degradation of the performances of the interferometer due to the amplification process is shown to be negligible.     

Investigation of the spectral content of a cw CO laser output using a high-resolution scanning Fabry-Perot interferometer

The use of a scanning Fabry-Perot interferometer of variable length (variable resolution) for investigating the output of a cw CO laser is reported. Under experimental conditions required to achieve maximum power it was found that the laser output consisted of two or more simultaneously occuring transitions due to the overlapping nature of the vibration- rotation bands. The frequency differences between these transitions were measured to an accuracy of 0.01 cm^-1. Operation of the CO laser on a single vibration-rotation transition was obtained by controlling the laser gain with the experimental variables of discharge pressure, gas temperature, and optical alignment. An alternative approach of obtaining monochromatic radiation, by using a Fabry-Perot interferometer as a frequency selective filter external to the CO laser, is reported.     

用于原子干涉仪实验的锂原子的塞曼减速与磁光囚禁

为了制备适于原子干涉仪实验的低温锂原子样品,开展了锂原子的塞曼减速及与磁光阱囚禁相关的实验研究.设计并实现了一种结构紧凑的腔体内冷式多级线圈叠加的塞曼减速器,将速度小于600 m/s的7Li原子减速到60 m/s,磁光阱装载速率为5×108/s,囚禁原子数目1×109个,原子团的最低温度约为220±30μK.研究了光学黏胶中7Li原子的寿命与囚禁光频率失谐量的关系.这些结果为进一步开展7Li原子亚多普勒冷却、光势阱蒸发冷却以及原子干涉仪实验奠定了基础.     

一种新颖的全光型表面原子(分子)漏斗

提出了一种产生全光型表面原子(分子)漏斗的新方案.采用红失谐高斯激光束照明由柱面透镜组成的光学系统，可在透镜焦平面附近产生横向漏斗形光强分布，以构成一表面光波导型原子漏斗.计算了漏斗的光强分布及其光学偶极势与偶极力分布.研究结果表明：该原子漏斗可用于冷原子(分子)的表面光波导、分束器和干涉仪以及微阱囚禁的有效装载，因而在集成原子光学及其原子芯片的研究中有着重要的应用. 关键词： 原子漏斗 分子漏斗 光学偶极势 原子芯片     

不同序列拉曼光脉冲对原子重力仪灵敏度的影响

研究了不同序列拉曼光脉冲对原子重力仪灵敏度的影响.结果表明,通过调节脉冲间隔可以改善原子干涉重力仪的灵敏度.在标准配置下,只考虑重力及一阶重力梯度时,三脉冲序列（π/2-π-π/2）的原子干涉重力仪具有较大的灵敏度,四脉冲序列（π/2-π-π-π/2）的原子干涉重力仪对重力不敏感,可用来测量重力梯度,五脉冲作用会降低原子干涉重力仪的灵敏度. 关键词： 原子重力仪 拉曼激光脉冲序列 灵敏度     

Dual-wavelength laser source for onboard atom interferometry

We present a compact and stable dual-wavelength laser source for onboard atom interferometry with two different atomic species. It is based on frequency-doubled telecom lasers locked on a femtosecond optical frequency comb. We take advantage of the maturity of fiber telecom technology to reduce the number of free-space optical components, which are intrinsically less stable, and to make the setup immune to vibrations and thermal fluctuations. The source provides the frequency agility and phase stability required for atom interferometry and can easily be adapted to other cold atom experiments. We have shown its robustness by achieving the first dual-species K-Rb magneto-optical trap in microgravity during parabolic flights.     

Two-frequency amplification in a semiconductor tapered amplifier for cold atom experiments

Simultaneous two-frequency amplification is highly desirable in cold atom experiments. The nonlinear response would appear in the two-frequency amplification with a semiconductor tapered amplifier(TA) and has a direct influence on the experimental result. We investigated in detail the effects of frequency difference, total power, and power ratio of two seeding lasers on the output components based on a simplified theoretical model. The simulation results showed that the multiple sideband generation in the amplifier due to self-phase and amplitude modulation could be suppressed and the TA tended to linearly amplify the power ratio between two-frequency components, when the two seeding lasers had a large frequency difference. This was verified experimentally in the output power ratio measurement via a calibrated Fabry-Perot interferometer method with a good linearity and an uncertainty of 1%. We also discussed the consequences of power ratio responses in the amplification in light of cold atom experiments, especially in the ac Stark shift related phase error of Raman-type atom interferometers(AIs). It was shown that the fluctuation of intensity ratio of Raman beams may induce significant systematic errors for an AI gyroscope.     

Decoherence dynamics in low-dimensional cold atom interferometers

We report on a study of the dynamics of decoherence of a matter-wave interferometer, consisting of a pair of low-dimensional cold atom condensates at finite temperature. We identify two distinct regimes in the time dependence of the coherence factor of the interferometer: quantum and classical. Explicit analytical results are obtained in both regimes. In particular, in the two-dimensional case in the classical (long time) regime, we find that the dynamics of decoherence is universal, exhibiting a power-law decay with an exponent, proportional to the ratio of the temperature to the Kosterlitz-Thouless temperature of a single 2D condensate. In the one-dimensional case in the classical regime we find a universal nonanalytic time dependence of decoherence, which is a consequence of the nonhydrodynamic nature of damping in 1D liquids.     

Highly accurate laser wavelength meter based on Doppler effect

We have built an accurate wavelength meter based on a Michelson interferometer characterized by a high stability velocity moving system. The unknown wavelength is determined from the Doppler frequency shifts of the output beams of the Michelson interferometer. The reference laser is a frequency stabilized helium-neon laser. A counting resolution of 2.6 × 10⁻⁹ for an integration time of 30 s has been obtained. The apparatus has been used to determine the wavelength of a second frequency stabilized helium-neon laser and the result has been compared to those given by two different methods: frequency beating in regards to the national reference and using a commercially available scanning-Michelson wavemeter. Taking into account the statistical errors, we achieved a relative accuracy on the unknown wavelength of 6.4 × 10⁻⁸ at 1σ.     

A simple laser system for atom interferometry

We present here a simple laser system for a laser-cooled atom interferometer, where all functions (laser cooling, interferometry and detection) are realized using only two extended cavity laser diodes, amplified by a common tapered amplifier. One laser is locked by frequency modulation transfer spectroscopy, the other being phase locked with an offset frequency determined by an field-programmable gate array-controlled direct digital synthesizer, which allows for efficient and versatile tuning of the laser frequency. Raman lasers are obtained with a double pass acoustooptic modulator. We demonstrate a gravimeter using this laser system, with performances close to the state of the art.