Integrated design of a compact magneto-optical trap for space applications

In this Letter, we describe an optical assembly that is designed for the engineering application of the atomic laser cooling techniques. Using a folded optical path scheme, we have built a miniaturized, compact magneto-optical trap(CMOT) for an87 Rb atomic fountain clock. Compared with the conventional magneto-optical traps used in other clocks, our system is more robust, more compact, more stable, and saves about 60% laser power. This optical setup has operated for about a year in our fountain system, passed the thermal cycle tests and the mechanical vibration and shock tests, and maintained a high performance without a need for realignment.     

Multi-beam method to increase the stability of bridge deflection measurement

The main limitation to the accuracy of the detection of a bridge deflection using laser-based optical solutions is atmospheric turbulence because of the laser beam propagation in ground proximity. The multi-beam method is presented to increase the stability of bridge deflection measurement. It is based on the use of a four-beam optical system and a subpixel resolution algorithm for the measurement of the deflection of a laser beam that propagates through the system. To obtain accurate results, different algorithms for measuring the position of the deflected beam in different optical systems are tested and compared. Based on this comparison, the four-beam method based on the macropixels iteration centroid and four-beam optical system is selected, and an accuracy of 0.16 pixels is obtained by the determination of the beam position in our setup. The proposed method is adopted to detect the bridge deflection and an accuracy of 0.01 mm is gained when the scintillation index C_n² is 3×10⁻⁴ m^−2/3.     

一套实用的铯原子喷泉光学系统的设计及建立

介绍了实现铯原子喷泉的过程及条件,并详细讨论了光路中各种光学元件对铯原子喷泉光学系统性能的影响。在对各种光学元件性能综合考虑的基础上,设计并建立了一套用于进行激光冷却和上抛的铯原子喷泉的光学系统,使光强控制、失谐调整、光束开关、光束质量等多种参量的控制达到了技术要求。在此基础上,实现了铯原子磁光阱,为实现铯原子喷泉奠定了基础。     

Pulsed laser deposition using diffractively shaped excimer-laser beams

Controlling laser-pulse parameters is an important issue in pulsed laser deposition (PLD). In particular, homogenization of laser beams improves the reproducibility of the PLD process by guaranteeing a uniform intensity distribution and a well-defined energy density of the laser spot on the target. We have integrated a beam-homogenization system into our PLD setup, and here we discuss the results and advantages of using such a system. The optical setup is based on diffractive beam-splitter gratings, which produce a 2×2-mm² flat-top distribution with fluences of the order of 3 J/cm² on the target. We demonstrate the applicability of this technique by depositing thin films of ferromagnetic Ni–Mn–Ga shape-memory alloys. Magnetic and structural characterization, including secondary ion mass spectrometry (SIMS), indicate that nearly stoichiometric composition and crystallization in the desired martensitic phase is obtained for films deposited on Al₂O₃ under optimal conditions. In contrast, the formation of silicide compounds at temperatures above 500 ^°C is detrimental in the deposition of Ni–Mn–Ga films directly on silicon.     

Fast wavefront sensing using a hardware parallel classifier chip

In most applications of laser technology and optics the beam quality, the ability to focus a laser beam and the achievement of a good optical resolution play an important role. The compensation of distortions using adaptive optics requires fast wavefront measurement. Classical wavefront analysis schemes use matrix operations, which show a nonlinear computation time dependence with matrix size, making it difficult to achieve high-speed control loops at a high resolution. A novel wavefront sensor system is presented using a massively parallel k-nearest neighbor classifier chip in an embedded hardware setup. Our miniaturized sensor is able to detect one optical distortion within about 80 μs allowing its use for high-speed adaptive optics applications.     

Experimental system for research on ultracold atomic gases near superconducting microstructures

We describe an experimental system that integrates the techniques for producing ultracold atomic gases with the techniques for cooling solid bodies to cryogenic temperatures. Ultracold clouds of ⁸⁷Rb are prepared in a trap setup based on room-temperature coils and subsequently transported to a superconducting microstructure by means of optical tweezers. The superconducting microstructure generates a magnetic microtrap and is cooled by a helium-flow cryostat that can achieve temperatures down to 2 K. Both the room-temperature trap setup and the superconducting microtrap are installed in the same ultra-high-vacuum chamber. The presented system is well suited to create hybrid quantum systems by combining ultracold atomic gases and superconducting devices.     

Optical-to-microwave frequency comparison with fractional uncertainty of 10-15

We report the technical aspects of the optical-to-microwave comparison for our recent measurements of the optical frequency of the mercury single-ion frequency standard in terms of the SI second as realized by the NIST-F1 cesium fountain clock. Over the course of six years, these measurements have resulted in a determination of the mercury single-ion frequency with a fractional uncertainty of less than 7×10^-16, making it the most accurately measured optical frequency to date. In this paper, we focus on the details of the comparison techniques used in the experiment and discuss the uncertainties associated with the optical-to-microwave synthesis based on a femtosecond laser frequency comb. We also present our most recent results in the context of the previous measurements of the mercury single-ion frequency and arrive at a final determination of the mercury single-ion optical frequency: f(Hg⁺)=1 064 721 609 899 145.30(69) Hz. PACS 06.30.Ft; 42.62.Eh; 32.30.Jc     

Quasi-monolithic ring resonator for efficient frequency doubling of an external cavity diode laser

A quasi-monolithic second-harmonic-generation ring resonator assembled with miniaturized components is presented. The ring contains a 10-mm-long bulk periodically poled lithium niobate crystal for second-harmonic generation, four plane mirrors and two gradient-index lenses. All parts are mounted on a glass substrate with an overall size of 19.5 mm×8.5 mm×4 mm. As pump source a broad-area laser diode operated in an external resonator with Littrow arrangement is utilized. This external cavity diode laser provides near diffraction limited, narrow-bandwidth emission with an optical output power of 450 mW at a wavelength of 976 nm. Locking of the diode laser emission to the resonance frequency of the ring cavity was achieved by an optical self-injection locking technique. With this setup more than 126 mW of diffraction-limited blue light at 488 nm could be generated. The opto–optical conversion efficiency was 28% and a wall plug efficiency better than 5.5% could be achieved.     

Multidimensional custom-made non-linear microscope: from ex-vivo to in-vivo imaging

We have built a custom-made multidimensional non-linear microscope equipped with a combination of several non-linear laser imaging techniques involving fluorescence lifetime, multispectral two-photon and second-harmonic generation imaging. The optical system was mounted on a vertical honeycomb breadboard in an upright configuration, using two galvo-mirrors relayed by two spherical mirrors as scanners. A double detection system working in non-descanning mode has allowed both photon counting and a proportional regime. This experimental setup offering high spatial (micrometric) and temporal (sub-nanosecond) resolution has been used to image both ex-vivo and in-vivo biological samples, including cells, tissues, and living animals. Multidimensional imaging was used to spectroscopically characterize human skin lesions, as malignant melanoma and naevi. Moreover, two-color detection of two photon excited fluorescence was applied to in-vivo imaging of living mice intact neocortex, as well as to induce neuronal microlesions by femtosecond laser burning. The presented applications demonstrate the capability of the instrument to be used in a wide range of biological and biomedical studies. PACS  87.64.mn; 78.47.Cd; 87.19.lw     

Paramagnetic particles in an optical trap

A setup based on an optical trap combined with homogeneous magnetic fields is presented. The system allows one to accurately control the alignment of multiple particles within the trap by controlling the external magnetic field. I study how two and three paramagnetic particles interact in the trap, and show that the experimental results can be explained in terms of dipolar interactions. It is also demonstrated that the system can be used to measure the magnetic moment of paramagnetic particles with a resolution of 10⁻¹⁵ Am².     

Melting behaviours of nickel nanorods

We report the synthesis and measurement of an ultra-precise and extremely stable optical frequency in the telecommunications window around 1543 nm. Using a fibre-based femtosecond frequency comb we have phase-stabilised a fibre laser at 194 THz to an optical frequency standard at 344 THz, thus transferring the properties of the optical frequency standard to another spectral region. Relative to the optical frequency standard, the synthesised frequency at 194 THz is determined to within 1 mHz and its fractional frequency instability is measured to be less than 2×10^-15 at 1 s, reaching 5× 10^-18 after 8000 s. We also measured the synthesised frequency against a caesium fountain clock: here the frequency comparison itself contributes less than 4 mHz (2×10^-17) to the uncertainty. Our results confirm the suitability of fibre based frequency comb technology for precision measurements and frequency synthesis, and enable long-distance comparison of optical clocks by using optical fibres to transmit the frequency information.     

The transportable cesium fountain clock NIM5: its construction and performance

The second laser cooling cesium fountain clock NIM5 at the National Institute of Metrology (NIM) China adopts the (1,1,1) direct optical molasses ( OM) configuration. NIM5 has been running with a stability of 3×10⁻¹⁵/d and an operation ratio of 99% since 2007. Preliminary evaluations of NIM5 in 2008 showed a typical combined uncertainty of 3×10⁻¹⁵. The NIM5 clock is operating in parallel with NIM’s first fountain clock NIM4. NIM4 and NIM5 are used to steer the frequency of the calculated NIM atomic time TA-c(NIM) and the first set of results are promising. We are now at the stage of comparing the frequency of NIM5 with UTC to support the independent frequency shift evaluations of NIM5 and contribute to the international atomic time in the near future.      

Highly sensitive laser-based sensor for nanoparticles in air using a dual-ring-mirror setup

One of the most frequently applied techniques to detect nanoparticles in air is analyzing laser light scattering. This technique is very flexible while offering high accuracy and reliability. Yet its functionality highly depends on the sensitivity of the measurement system components. Especially for miniaturized sensor devices with limited space, additional techniques are needed to preserve high intensity of scattered light. In our work we demonstrate a technique using two spherical ring mirrors to identify nanoparticles with diameters below 100 nm in a forward-scattering setup. We succeeded measuring polystyrene particles with diameters of 92 nm with a signal-to-noise-ratio of more than 10.     

A laser setup for rubidium cooling dedicated to space applications

We present the complete characterization of a laser setup for rubidium cooling dedicated to space applications. The experimental setup is realized with commercial off-the-shelf fiber components suitable for space applications. By frequency doubling two fiber laser diodes at 1560 nm, we produce the two optical frequencies at 780 nm required for atomic cooling of ⁸⁷Rb. The first laser is locked on saturated absorption signal and long-term frequency drift has been canceled using a digital integrator. The optical frequency of the second laser is controlled relatively to the first one by a frequency comparison method. A full characterization of the setup, including frequency stability evaluation and frequency noise measurement, has been performed. The optical frequency doubling module has been submitted to environmental tests to verify its compatibility with space applications.     

Experimental progress in gravity measurement with an atom interferometer

Precisely determining gravity acceleration g plays an important role on both geophysics and metrology. For gravity measurements and high-precision gravitation experiments, a cold atom gravimeter with the aimed resolution of 10.⁻⁹g/Hz^1/2 (1 g=9.8 m/s²) is being built in our cave laboratory. There will be four steps for our ⁸⁷Rb atom gravimeter, Magneto-Optical Trap (MOT) for cooling and trapping atoms, initial state preparation, π/2-π-π/2 Raman laser pulse interactions with cold atoms, and the final state detection for phase measurement. About 108 atoms have been trapped by our MOT and further cooled by moving molasses, and an atomic fountain has also been observed.      

An ultra-stable referenced interrogation system in the deep ultraviolet for a mercury optical lattice clock

We have developed an ultra-stable source in the deep ultraviolet, suitable to fulfil the interrogation requirements of a future fully-operational lattice clock based on neutral mercury. At the core of the system is a Fabry–Pérot cavity which is highly impervious to temperature and vibrational perturbations. The mirror substrate is made of fused silica in order to exploit the comparatively low thermal noise limits associated with this material. By stabilizing the frequency of a 1062.6 nm Yb-doped fiber laser to the cavity, and including an additional link to LNE-SYRTE’s fountain primary frequency standards via an optical frequency comb, we produce a signal which is both stable at the 10^?15 level in fractional terms and referenced to primary frequency standards. The signal is subsequently amplified and frequency-doubled twice to produce several milliwatts of interrogation signal at 265.6 nm in the deep ultraviolet.     

Broadband amplitude-modulated laser source with high output power for FM/cw lidar transmitter

We are building a long-range FM/cw nonscanning imaging lidar breadboard. This lidar system achieves ranging based on a frequency modulation/continuous wave (FM/cw) technique, implemented by an amplitude modulated mid-IR diode laser transmitter with a linear frequency modulation (LFM) of the subcarrier. Firstly, various schemes of light beam modulation are analyzed. Secondly, we put forward a laser modulation scheme whose core was formed by a 1.55 μm electro-absorption modulated laser diode (EML) and an erbium-doped optical fiber amplifier (EDFA), then a corresponding experimental system architecture and components for light beam modulation and detection are established. Finally, a corresponding experiment of laser beam modulation is completed for the first time. In our experiment, the EML amplitude is modulated by a 200 MHz to 800 MHz LFM signal, whose amplitude value is 2.05 V. The average output power of the modulated laser obtained in the experiment is 10 W, peak power is 16.4 W, and the average modulation depth is 78%. The results of tests predict that this laser modulation scheme is likely to improve the imaging range of the FM/cw lidar.     

Endoscopic optical probe with a PZT actuator and MR tracker

A miniaturized optical probe with a magnetic-resistance (MR) position tracker and piezoelectric-transduce (PZT) mirror system was developed for endoscopic optical imaging. All of the optical components such as collimation and focal lenses, reflection mirror, PZT linear actuator and MR sensor were wholly packaged in a single scanning probe with a volume of 3.57 cm³. This endoscopic probe has the advantages of having a small volume, extended stroke length (4.5 mm), high scanning speed (18.2 mm/s), efficient recoupling ratio (78.3%) and high spatial resolution (11.7 μm) compared to conventional endoscopes. Consequently, it showed the potential for improving the endoscopic imaging system and utilizing the image-guided robotic surgery system.     

Iron-57 Mössbauer spectroscopic study of fluorinated strontium orthoferrite

A nuclear spin maser of a new type, that employs a feedback scheme based on optical nuclear spin detection, has been fabricated. The spin maser is operated at a low static field of 30 mG by using the optical detection method. The frequency stability and precision of the spin maser have been improved by a highly stabilized current source for the static magnetic field. An experimental setup to search for an electric dipole moment (EDM) in ¹²⁹Xe atom is being developed.     

一种新颖的表面空心微光阱阵列

提出了采用四台阶相位光栅与微透镜阵列组合产生一种新颖的表面空心微光阱阵列的方案，研究了表面空心微光阱阵列的光强分布，计算了相应的光学囚禁势，并讨论了该微光阱阵列在原子分子光学中的潜在应用.研究表明当用1W的YAG激光照射时，在1cm²面积上可产生近10⁴个空心光阱，每个光阱具有较小的囚禁体积和较大的有效光强及其强度梯度，对⁸⁵Rb原子的光学囚禁势可达190μK.如此深的光阱足以囚禁冷原子或冷分子，并可用于实现全光型原子或分子玻色-爱因斯坦凝聚，甚至制备新颖的光学晶格等. 关键词： 空心光阱 冷原子或冷分子 光学晶格