2006, 4(9) Column
Chinese Optics Letters 第4卷 第9期
A new scheme to realize a two-dimensional (2D) array of magnetic micro-lenses for a cold atomic beam, formed by an array of square current-carrying wires, is proposed. We calculate the spatial distributions of the magnetic fields from the array of current-carrying wires and the magnetic focusing potential for cold rubidium atoms, and study the dynamic focusing processes of cold atoms passing through the magnetic micro-lens array and its focusing properties by using Monte-Carlo simulations and trajectory tracing method. The result shows that the proposed micro-lens array can be used to focus effectively a cold atomic beam, even to load ultracold atoms or a BEC sample into a 2D optical lattice formed by blue detuned hollow beams.
020.0020 Atomic and molecular physics 220.3620 Lens design 220.2560 Focus 020.7490 Zeeman effect Rate coefficients for energy-pooling (EP) collisions Rb(5P_(J))+Cs(6P_(3/2))-->Rb(5S_(1/2))+Cs(nl_(J')) have been measured. Atoms were excited to Rb(5P_(J)) and Cs(6P_(3/2)) states using two single-mode diode lasers. To isolate the heteronuclear contribution in the fluorescence spectrum, a double-modulation technique has been adopted. The excited-atom density and spatial distribution are mapped by monitoring the absorption of a counterpropagating single-mode diode laser beam, tuned to Rb(5P_(J)-->7S_(1/2)) and Cs(6P_(3/2)-->8S_(1/2)) transitions respectively, which could be translated parallelly to the pump beams. The excited atom densities are combined with the measured fluorescence ratios to determine cross sections for the EP processes. It was found that Rb(5P_(J))+Cs(6P_(3/2)) collisions are more efficient than Rb(5P_(3/2))+Cs(6P_(3/2)) collisions for populating Cs(4F_(5/2)), while the opposite is true for populating Cs(4F_(7/2)).
020.0020 Atomic and molecular physics 020.2070 Effects of collisions 020.3690 Line shapes and shifts An improved algorithm based on the layer peeling (LP) method is proposed and demonstrated. The new method is shown to be effective for mitigating the impact of numerical errors on reconstruction of coupling function for strongly reflecting Bragg gratings. As examples, a flat-top dispersion-free fiber grating and a fiber-grating dispersion compensator are designed by the improved LP method. For a chirp grating, more accurate results are demonstrated in comparison with those obtained by the integral layer peeling (ILP) method.
230.1480 Bragg reflectors 050.2770 Gratings 290.3200 Inverse scattering 060.2340 Fiber optics components 060.4510 Optical communications Analysis on Raman gain coefficients in polarization maintaining photonic crystal fibersDownload:524次
The Raman gain coefficients in polarization maintaining photonic crystal fibers (PM-PCFs) are analyzed in order to design fibers for linearly polarized Raman fiber laser with enhanced performances. The results show that a well designed germanium-doped PM-PCF can attain the value of Raman gain coefficient over 50 /(W.km), going with very high birefringence and single mode operation at 1.55-micron signal wavelength and 1.45-micron pump wavelength.
060.0060 Fiber optics and optical communications 060.2420 Fibers, polarization-maintaining 140.3550 Lasers, Raman Fabrication and characteristics of character-1 shaped reduced diameter polarization-maintaining optical fiberDownload:857次
A novel structure reducing diameter polarization maintaining optical fiber with high birefringence and strength is introduced. The fiber is fabricated through using modified chemical vapor deposition (MCVD) method, which is able to produce the optimum predicted character-1 shaped fiber structure. As a result, a low-loss fiber with beat length close to 2.0 mm at 1310 nm wavelength and extinction ratio approximately -25 dB has been produced. The process is both simple and reproducible.
060.0060 Fiber optics and optical communications 060.2280 Fiber design and fabrication 060.2420 Fibers, polarization-maintaining 060.2800 Gyroscopes Simple Strehl ratio based method for pupil phase mask's optimization in wavefront coding systemDownload:691次
By applying the wavefront coding technique to an optical system, the depth of focus can be greatly increased. Several complicated methods have already been taken to optimize for the best pupil phase mask in ideal condition. Here a simple Strehl ratio based method with only the standard deviation method used to evaluate the Strehl ratio stability over the depth of focus is applied to optimize for the best coefficients of pupil phase mask in practical optical systems. Results of imaging simulations for optical systems with and without pupil phase mask are presented, and the sharpness of image is calculated for comparison. The optimized pupil phase mask shows good results in extending the depth of focus.
070.0070 Fourier optics and optical signal processing 090.1000 Aberration compensation 100.3020 Image reconstruction-restoration 110.0110 Imaging systems 120.5060 Phase modulation Frequency stabilization of a laser-diode-module-pumped single-frequency Cr,Nd:YAG laserDownload:570次
A single-frequency passively Q-switched laser was constructed, in which a co-doped crystal served as an active element, a mode selector, and a passive Q-switch simultaneously. In order to obtain the frequency instability of 10^(-6), a stable single-frequency operation was presented and its characteristics were determined. The experimental results showed that the stable single frequency could be maintained for half an hour and the linewidth was approximately 530 MHz at a pump power of 13 W.
140.6810 Thermal effects 140.3570 Lasers (single-mode) 140.3480 Lasers, diode-pumped 350.2770 Gratings 350.2450 Filters, absorption High power single-mode large-mode-area photonic crystal fiber laser with improved Fabry-Perot cavityDownload:667次
An Yb3+-doped double-clad large-mode-area photonic crystal fiber (LMA PCF) laser with 103-W single-mode continuous-wave output power is demonstrated using an improved Fabry-Perot (F-P) configuration. The slope efficiency of 83.2% and good beam quality (M2=1.2+-0.1) are achieved without any thermo-optical problems, dichroic mirror surface damage, and drop of the slope efficiency in this system.
140.3480 Lasers, diode-pumped 140.3510 Lasers, fiber 060.2430 Fibers, single-mode A compact extended cavity diode laser (ECDL) system operating at 852 nm for small optically pumped cesium (Cs) beam frequency standards was reported. ECDL and a saturated absorption spectroscopy setup were all built in an aluminum box with dimension of 10*10*7 (cm). ECDL was based on a Littman-Metcaff configuration, whose free-running linewidth was less than 600 kHz. A digital automatic frequency lock unit (AFLU) was developed to lock the laser frequency to specify Cs absorption lines automatically and re-lock it in case of lock broken. With AFLU, the laser frequency was continuously locked for several weeks.
140.2020 Diode lasers 300.6460 Spectroscopy, saturation 120.4570 Optical design of instruments An experimental method for calibration of optical trap force upon cells by use of electrokinetic phenomena is demonstrated. An electronkinetic sample chamber system (ESCS) is designed instead of a common sample chamber and a costly automatism stage, thus the experimental setup is simpler and cheaper. Experiments indicate that the range of the trap force measured by this method is piconewton and sub-piconewton, which makes it fit for study on non-damage interaction between light and biological particles with optical tweezers especially. Since this method is relevant to particle electric charge, by applying an alternating electric field, the new method may overcome the problem of correcting drag force and allow us to measure simultaneously optical trap stiffness and particle electric charge.
170.1530 Cell analysis 170.3890 Medical optics instrumentation 200.4880 Optomechanics By using one-dimensional self-consistent relativistic fluid model, a novel type of moving relativistic electromagnetic solitons with high intensity in electron-ion plasmas where the ion dynamics is taken into account is investigated numerically. Unlike solitons with single-humped scalar potential found in previous studies, these solitons possess multi-humped scalar and vector potential. The existence of such soliton solutions is investigated in plasmas with different background densities, and the properties of these solitons are presented in detail. We found that the peculiar profile of electron density has alternating regions of humps and dips like a Bragg grating.
320.0320 Ultrafast optics 000.6800 Theoretical physics 190.5530 Pulse propagation and solitons The intensity-dependent two-photon absorption and nonlinear refraction coefficients of GaP optical crystal at 800 nm were measured with time-resolved femtosecond pump-probe technique. A nonlinear refraction coefficient of 1.7*10^(-17) m2/W and a two-photon absorption coefficient of 1.5*10^(-12) m/W of GaP crystal were obtained at a pump intensity of 3.5*10^(12) W/m2. The nonlinear refraction coefficient saturates at 3.5*10^(12) W/m2, while the two-photon absorption coefficient keeps linear increase at 6*10^(12) W/m2. Furthermore, fifth-order nonlinear refraction of the GaP optical crystal was revealed to occur above pump intensity of 3.5*10^(12) W/m2.
190.4720 Optical nonlinearities of condensed matter 320.1590 Chirping 320.0320 Ultrafast optics A widely and continuously tunable optical parametric generator (OPG) pumped by a 1064-nm acousto-optically Q-switched diode-end-pumped Nd:YAG laser based on MgO-doped periodically poled LiNbO3 crystal with a multigrating structure (29.2-30.4 micron) is reported. A broad continuous signal spectrum of 1513-1700 nm is obtained by changing the crystal grating periods from 29.2 to 30.4 micron and by tuning the crystal temperature from 30 to 180 Celsius degrees simultaneously. When the average pump power is 1.82 W with pulse duration of about 70 ns operating at a repetition rate of 10 kHz, the maximum signal output power of the periodically poled MgO-doped lithium niobate (PPMgLN) OPG is about 210 mW corresponding to the idler and total powers of 118.4 and 328.4 mW respectively.
190.4970 Parametric oscillators and amplifiers 140.3600 Lasers (tunable) 140.3070 Infrared and far-infrared lasers A new set of tunable phase-only filters for realizing the transverse superresolution is introduced. The filters, whose significant features are their ability to tune and simplicity, consist of one half-wave plate between two quarter-wave plates, and the half-wave plate is made of two zones that can rotate with respect to each other. Through analyzing the transverse point spread function of such system, it can be concluded that by rotating any zone of the half-wave plate, the transverse resolution can be realized and can be tunable.
230.6120 Spatial light modulators 100.6640 Superresolution 120.2440 Filters This paper addresses the estimation of adjacency effect of CBERS-2 image. The adjacency effect influences the digital number (DN) value of a pixel by adding surrounding scattering signals and path scattering signals. Based on the theory of radiation transfer model, a procedure is designed to measure the reflectance from the surface target materials and the materials in a box, which is 1.5 m above the surface to avoid upwelling reflectance. The results show that the adjacency effect varies from visible, near infrared and becomes steady within short infrared wavelength region; the adjacency effect weakens with the increase of distance between testing sites. The adjacency effect of CBERS-2 image is corrected and the quality of the resulting image is improved.
290.4210 Multiple scattering 110.4850 Optical transfer functions 110.2990 Image formation theory 120.4820 Optical systems Determination of the deposition rate of DC magnetron sputtering in fabrication of X-ray supermirrorsDownload:545次
X-ray supermirror is a non-periodic multilayer structure, whose optical performance is greatly affected by the stability and accuracy of the deposition rate in the fabrication using the direct current (DC) magnetron sputtering. By considering the location-setting time of the substrate positioning above the sputtering target, the deposition rate can be accurately determined. Experimental results show that the optical performance of the supermirror is in agreement with the design aim, which indicates that the layer thickness is well controlled and coincides with the desired ones.
220.0220 Optical design and fabrication 230.0230 Optical devices 310.0310 Thin films 340.0340 X-ray optics Video stabilization with sub-image phase correlationDownload:529次
A fast video stabilization method is presented, which consists of sub-image phase correlation based global motion estimation, Kalman filtering based motion smoothing and motion modification based compensation. Global motion is decided using phase correlation in four sub-images. Then, the motion vectors are accumulated to be Kalman filtered for smoothing. The ordinal motion compensation is applied to each frame with modification to prevent error propagation. Experimental results show that this stabilization system can remove unwanted translational jitter of video sequences and follow intentional scan at real-time speed.
330.4150 Motion detection 040.7290 Video 100.2000 Digital image processing Design and fabrication of one-dimensional focusing X-ray compound lens with Al materialDownload:503次
A method based on Fourier spectrum analysis for predicting the performances of the X-ray compound lenses is briefly introduced, the theoretical result obtained is the same as that of Fresnel-Kirchhoff approach. A kind of technique named moulding is developed for fabricating the one-dimensional (1D) compound X-ray lens with Al material and the fabrication process is presented. In addition, a two-time coating method is used to improve the numerical apertures of the compound lenses. Furthermore, the focusing performance of the Al compound X-ray lens under the high energy X-rays is measured.
340.0340 X-ray optics 070.2590 Fourier transforms 220.4000 Microstructure fabrication 动态信息
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