采用随机振动法抑制白光处理系统中的颗粒噪声

本文提出在白光信息处理中,可通过使滤波孔在傅里叶面彩虹状衍射谱附近做随机振动的方法,达到抑制光栅编码片的振幅型颗粒噪声.改善其输出信噪比的目的,并给出了相应的实验结果.     

Spectroscopy of francium in a magneto optical trap

The francium atom offers an excellent laboratory to study electron-nucleus interactions. As the heaviest alkali, its atomic properties can be calculated with high precision, and laser trapping methods now allow precision optical spectroscopy of many isotopes. Recent measurements of the 7P_1/2 hyperfine structure, when coupled with previous measurements of the ground state hyperfine structure reveal a hyperfine anomaly. The change in anomaly between an even-N isotope and an odd-N isotope is sensitive to the radial distribution of the neutron magnetization. This revised version was published online in August 2006 with corrections to the Cover Date.     

Spectral estimation method for noisy data using a noise reference

The development of array processing methods to extract the useful characteristics of acoustic sources such as their locations and absolute levels, starting from the measured sound field is one of the main issues in aero-acoustics. The conventional beamforming method is a very popular technique investigated to solve the power level estimation problem. It has the advantage of being robust, easy to implement and cheap in computation time. However, this technique is also known for having poor spatial resolution capabilities which prevents the correct source levels being obtained for numerous practical applications. Deconvolution techniques of the result computed with CBF, with the point spread function of the array manifold, may restore the power levels of the acoustic sources that would be observed in the absence of the array resolution effects. However, the accuracy of the results provided by deconvolution methods is very sensitive to background noise, always present in acoustic measurements. This process should be carried out after the additive noise has been suitably attenuated and, ideally, the deconvolution operator should amplify the noise as little as possible. Another approach is described in the article. It consists in using a noise reference and a new technique called spectral estimation method with additive noise to remove both the smearing effect produced by the array response and the background noise. The technique has been applied to computer and experimental simulations conducted both in an anechoic chamber and in the test section of an open wind tunnel involving acoustic sources radiating in a noisy environment. The levels of the sources were found with a good level of accuracy and the background noise greatly reduced, confirming the validity of the approach and the satisfactory performance of the method proposed.     

Single atoms transferring between a magneto-optical trap and a far-off-resonance optical dipole trap

Based on our work on single cesium atoms trapped in a large-magnetic-gradient vapour-cell magneto-optical trap (MOT), the signal-to-noise ratio (SNR) is remarkably improved. Also a far-off-resonance optical dipole trap (FORT) formed by a strongly-focused 1064~nm single frequency Nd:YVO₄ laser beam is introduced. One cesium atom is prepared in the MOT, and then it can transfer successfully between the MOT and the FORT which is overlapped with the MOT. Utilizing the effective transfer, the lifetime of single atoms trapped in the FORT is measured to be 6.9± 0.3~s. Thus we provide a system where the atomic qubit can be coherently manipulated.     

Suppression of beating noise of narrow-linewidth erbium-doped fiber ring lasers by use of a semiconductor optical amplifier

Beating noise in narrow-linewidth erbium-doped fiber ring lasers puts severe limitations on applications of the lasers. We demonstrate the suppression of beating noise in fiber ring lasers by using a semiconductor optical amplifier in the laser cavity, which acts as a high-pass filter. Two different ring structures are presented as examples to demonstrate this beating noise suppression.     

Suppression of ring-down in noise spectroscopy

Suppression of systematic noise artifacts which complicate the understanding of broadline NMR spectra remains a difficult problem. Many strategies for canceling noise have evolved; many appear designed for very specific hardware implementations. In this paper we address the problem of artifact suppression in noise-based (stochastic) NMR, where low power pulses applied at high duty cycle are used to probe the spectral frequencies found in an NMR or NQR experiment. While typical peak powers are reduced by four to six orders of magnitude as compared to conventional NMR experiments, this power reduction corresponds only to an approximate halving of the idealized electronic ring-down in a tuned circuit; where other systematic sources of noise contribute, the recovery time advantage of noise spectroscopy may be larger or smaller. We suggest a simple experimental modification which exploits the linear response properties of nuclear spins in the presence of small rotations to demonstrate how ring-down—from whatever source—can be substantially eliminated as a problem in noise spectroscopy. This should provide substantial improvements in quantitation and lineshape measurements in NMR spectra of many solid state systems.     

光阱中布朗粒子动力学分析

通过对光阱中的布朗粒子进行动力学方程求解,由解的结果分析得到观测系统的性能要求．结果表明：光阱中布朗颗粒服从Boltzmann分布;对其运动的观测需要纳米量级的空间分辨率和毫秒量级的时间分辨率．     

基于磁悬浮大体积交叉光学偶极阱的Dimple光阱装载研究

三维拉曼边带冷却后的铯原子样品装载于一个磁悬浮的大体积交叉光学偶极阱中, 继续加载一个小体积的光学偶极阱后, 实现了Dimple光学偶极阱对铯原子的高效装载. 对不同磁场下磁悬浮大体积光阱的有效装载势能进行理论分析与实验测量, 得出最优化的梯度磁场和均匀偏置磁场, 获得了基于磁悬浮大体积光阱的Dimple光学偶极阱的装载势能曲线, 实现了Dimple光学偶极阱对经拉曼边带冷却后俘获在磁悬浮的大体积光阱中的铯原子样品的有效装载. 比较了Dimple光学偶极阱分别从拉曼边带冷却、大体积的交叉光阱和消除反俘获势后的磁悬浮大体积光阱装载的结果, 将俘获在磁悬浮大体积光阱中的铯原子样品装载到Dimple光学偶极阱, 铯原子样品的密度提高了约15倍.     

Collisions in a cesium hybrid optical and magnetic trap

A new scheme for trapping Cs atoms in a non dissipative trap has been developed. The trap involves both optical dipole forces and magnetic forces. This device is suitable for Cs atoms in the lowest energy Zeeman sublevel, thus avoiding the two-body inelastic collisions which prevented reaching Bose-Einstein condensation of Cs in purely magnetic traps. Furthermore, an additional magnetic field can be applied, allowing a fine tuning of the two-body elastic collision cross-section. We report on the experimental realization of such a trap and describe the characteristics of the trapped atomic sample. An analysis of the collisional regime is performed using measurements of the damping of the oscillatory modes of the trapped atom cloud.     

Mott transition of fermionic atoms in a three-dimensional optical trap

We study theoretically the Mott metal-insulator transition for a system of fermionic atoms confined in a three-dimensional optical lattice and a harmonic trap. We describe an inhomogeneous system of several thousand sites using an adaptation of dynamical mean-field theory solved efficiently with the numerical renormalization group method. Above a critical value of the on-site interaction, a Mott-insulating phase appears in the system. We investigate signatures of the Mott phase in the density profile and in time-of-flight experiments.     

Cavity enhanced measurement of trap frequency in an optical dipole trap

We demonstrate a direct, fluorescence-free measurement of the oscillation frequency of cold atoms in an optical dipole trap based on a high-finesse optical cavity strongly coupled to atoms. The parametric heating spectra of the trapped atoms are obtained by recording the transmitted photons from the cavity with the trap depth is modulated by different frequency.Moreover, in our method the oscillation can be observed directly in the time scale. Being compared to the conventional fluorescence-dependent method, our approach avoids uncertainties associated with the illuminating light and auxiliary imaging optics. This method has the potential application of determining the motion of atoms with stored quantum bits or degenerate gases without destroying them.     

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.     

Bose–Einstein condensates in a ring optical lattices trap

The evolution of Bose–Einstein condensates (BECs) loaded into a periodic ring optical lattices (OL) trap is studied. By means of the variational method and direct numerical simulations of the Gross–Pitaevskii (GP) equation, the ground state properties and the vortex stabilities of the condensates for both repulsive and attractive cases are investigated. The results show that the bound states exist for determinate OL strength and interatomic interaction. However, the ground states of BECs undergo delocalizing–localizing transition for both attractive and repulsive cases as the strength of the OL or the interatomic interaction is decreased below the critical value. The ring OL can suppress the delocalizing transition efficiently.     

Suppression of intensity noise in a diode-pumped Tm-Ho:YAG laser

We investigate the intensity noise induced by pump-power fluctuations in a diode-pumped single-frequency codoped Tm-Ho:YAG laser and we measure, in the frequency domain, the corresponding transfer function. Good agreement between the measured transfer functions and the theoretical prediction is found. A relative intensity-noise level of ~- 110 dB/Hz from ~1 kHz to the relaxation-oscillation frequency, with complete suppression of the relaxation-oscillation peak, is achieved by use of a suitable optoelectronic feedback circuit.     

Observation of nonlinear optical recoil-induced resonances in a dark magneto-optical trap

Nonlinear optical recoil-induced resonances have been observed in a gas of cold rubidium atoms trapped in a dark magneto-optical trap. These resonances are used to measure the temperature and velocity distribution of the cold atoms. The velocity distribution of the atoms in the dark magneto-optical trap has an excessive amount of fast atoms as compared to the Maxwell distribution and to the distribution in a standard magneto-optical trap.     

Microfabricated surface ion trap on a high-finesse optical mirror

A novel approach to optics integration in ion traps is demonstrated based on a surface electrode ion trap that is microfabricated on top of a dielectric mirror. Additional optical losses due to fabrication are found to be as low as 80 ppm for light at 422 nm. The integrated mirror is used to demonstrate light collection from, and imaging of, a single Sr88(+) ion trapped 169±4 μm above the mirror.     

Microbead dynamics in optical trap assisted nanopatterning

An optically pumped ZnO nanowire laser with a 10-period SiO₂/SiN _x distributed Bragg reflector (DBR) was demonstrated. Stimulated emissions with equally distributed Fabry–Pérot lasing modes were observed at pumping powers larger than 121 kW/cm². This result, when compared to nanowires of the same length and without a DBR structure, shows that a lower threshold of pumping power, higher quality factor, and larger cavity finesse can be achieved due to the high reflectivity of the DBR in the designed wavelength range. A coexistence of stimulated and spontaneous emissions was also observed above threshold and was attributed to partially confined waveguide modes in nanowires with diameters smaller than 100 nm.