We propose a novel scheme to form one- and two-dimensional arrays of double-well optical dipole traps for cold atoms (or molecules) by using an optical system composed of a binary π-phase grating and a lens illuminated by a plane light wave, and study the relationship between the maximum intensity Imax of each optical well (or the maximum trapping potential Umax for 85Rb atoms) and the relative aperture β ( = a/f) of the lens. We also calculate the intensity gradients of each optical well and their curvatures, and estimate the spontaneous photon-scattering rate of trapped atom in each well, including Rayleigh and Raman scattering rates. Our study shows that the proposed 1D and 2D arrays of double-well traps can be used to prepare 1D and 2D novel optical lattices with cold atoms (or molecules), or form an all-optically integrated atom optical chip, or even to realize an array of all-optical double-well atomic (or molecular) Bose–Einstein condensates by optical-potential evaporative cooling, and so on.
In order to generate a submicron localized hollow laser beam and realize the more efficient laser cooling and trapping of a single atom, a simple and promising scheme with using the system of a single mode fiber a circle binary phase plate and a microlens is proposed in this paper. From Rayleigh-Sommerfeld diffraction theory, the intensity distribution of the generated localized hollow laser beam near the focal plane and its propagating properties in free space are calculated. Also, the dependences of the dark-spot size of the localized hollow beam on the mode radius of single mode fiber and the focal length of the mocrolens are studied. The calculated results show that the intensity distribution of the localized hollow beam presents approximately symmstrical distribution near the focal plane. In the center of the focal plane, the light intensity is 0 and increases gradually around it. So a closed spherical light field (i.e., localized hollow laser beam) with a radius of 0.4 m is generated. The calculated results also show that the dark-spot size of the localized hollow laser beam decreases with the increasing of the microlens focal length and the decreasing of the single mode fiber mode radius. So proper parameters of this optical system can be chosen to generate localized hollow laser beams with different sizes for various applications. When the localized hollow laser beam is blue detuned, atoms will be trapped in the minimum light filed. If a repumping laser beam is applied, the trapped atoms will be also cooled by the intensity-gradient Sisyphus cooling. In this paper, we build a device for trapping and cooling a single atom by using the generated blue detuned submicron localized hollow laser beam. We study the dynamical process of intensity-gradient cooling of a single 87Rb atom trapped in the localized hollow beam by Monte-Carlo method. Our study shows that a single 87Rb atom with a temperature of 120 K (the corresponding momentum is 30ħk) from a magneto-optical trap (MOT) can be directly cooled to a final tempreture of ～ 5.8 K (the corresponding momentum is ～ 6.6ħk). So an ultracold single atom is generated and trapped in our submicro localized hollow beam. This device for obtaining ultralcold single atom can be widely uesd in the regions of the optical physics, the atom and molecule optics, such as the detecting of the fundamental physical parameters, realizing the quantum computer, studying the cold collision of singe atoms, and realizing the single atom laser.
On the basis of the dressed-atom model, the general analytic expressions for the eigenenergies, eigenstates and their optical potentials of the Λ-configuration three-level atom system are derived and analysed. From the calculation of dipole matrix element of different dressed states, we obtain the spontaneous-emission rates in the dressed-atom picture. We find that our general expressions of optical potentials for the three-level dressed atom can be reduced to the same as ones in previous references under the approximation of a small saturation parameter. We also analyse the dependences of the optical potentials of a three-level 85Rb atom on the laser detuning and the dependences of spontaneous-emission rates on the radial position in the dark hollow beam, and discuss the probability (population) evolutions of dressed-atomic eigenstates in three levels in the hollow beam.
Laser cooling of solid material has become a new developing research area in recent years. Tm3+ doped ZrF4-BaF2-LaF3-AlF3-NaF-PbF2 glass is one of the hot materials in this field. Compared with Yb3+, Tm3+ has better cooling potential. Up to date, one of the main factors restricting the cooling effect is fluorescent reabsorption. In this paper, firstly, using several spectral parameters of Tm3+, the reabsorption effect is calculated by stochastic model which is a semianalytical approach to this problem. The average number of absorption events is obtained. Afterwards, the effect of fluorescence trapping due to total internal reflection is analyzed. The results show that the quantum efficiency will be lowed by 0.5%1% due to reabsorption, that the redshift of the mean fluorescence wavelength is in the range of 210 nm, and that the cooling efficiency and the cooling power decrease. Finally, after discussion, we find that the use of a small size and a long thin geometry will benefit to the fluorescence emission and cooling effect.
We have calculated the Stark effect of CH3F molecules in external electrical fields, the rotational population of supersonic CH3F molecules in different quantum states, and analyse the motion of weak-field-seeking CH3F molecules in a state | J = 1, KM = −1〉 inside the electrical field of a Stark decelerator by using a simple analytical model. Three-dimensional Monte Carlo simulation is performed to simulate the dynamical slowing process of molecules through the decelerator, and the results are compared with those obtained from the analytical model, including the phase stability, slowing efficiency as well as the translational temperature of the slowed molecular packet. Our study shows that with a modest dipole moment (~1.85 Debye) and a relatively slight molecular weight (~34.03), CH3F molecules in a state |J = 1, KM = −1〉 are a good candidate for slowing with electrostatic field. With high voltages of ±10 kV applied on the decelerator, molecules of 370 m/s can be brought to a standstill within 200 slowing stages.
Laser cooling of solids is also called anti-Stokes fluorescent cooling, it is a new optical cooling technology in recent years. We propose a two-level model to analyze the absorption and stimulated-emission processes between the Yb3+2F7/2 ground-state manifold and the 2F5/2 excited-state manifold, and discuss several parameters that influence the cooling power, and find some ways to improve the cooling power. The influences of the doped concentration, pumping power and the effective pump-spot area on cooling are particularly analyzed. At the same time, we make computer simulation about the cooling process and obtain the temperature as a function of the cooling time, which is similar to the experimental results. So this shows that our model is reasonable.
Using exact solutions of Maxwell equations based on the vector model, we calculate the diffracted near- and far-field distributions of the HE11-mode output beam from a micron-sized hollow optical fibre under the Fresnel approximation, and compare the differences between the HE11- and LP01-mode output beams. Our study shows that it is unsuitable to calculate the diffracted near-field distribution of the hollow fibre by using weakly waveguiding approximation, and the near- and far-field intensity distributions of the HE11-mode output beam are doughnut-like, which can be used to form a simple atomic funnel as it is blue-detuned.
The transformation of DIN (Dissolved Inorganic Nitrogen) and nitrification and denitrification processes in near sea section of Zhujiang River were studied. And nine sampling sites, three sampling sites for sediment among them, were located along Zhujiang River from Zhongshan Universty dock to Longxu water course.The values of water parameters showed that there are notably positive correlations between the concentrations of ammonium and COD, phosphate, and silicate. But the correlation between ammonium and nitrate was obviously negative (R=-0.97, n=19). About 88% ammonium was converted to nitrate from ST1 to ST9. The distribution tendency of nitrate concentrations was increased toward the sea opposite to the other factors as a consequence of ammonium oxidation during flowing into the sea. The concentrations of nitrous oxide varied between 57～329nmol·L~(-1), and the saturation ware from 674%～4134%.It suggested that the area was an emissive source of nitrous oxide. The acetylene inhibition technique was employed to evaluate the rates of nitrification, denitrification and nitrate reduction by bacterial activities. The average of nitrification, denitrification and nitrate reduction rates ranged from 0.32 to 2.43mmol·m~(-2)·h~(-1), 0.03 to 0.84(mmol·m~(-2)·h~(-1)) and 4.17 to 13.06mmol·m~(-2)·h~(-1) respectively. The vertical profiles of the sediments showed that the nitrification and denitrification processes mainly took place in the depths from 0 to 4cm and there were differences among these sampling sites. The rates of nitrification, denitrification and nitrate reduction were dominated by Eh, nitrate and ammonium concentrations in sediment and DO in overlay water.
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