We build a Zeeman slower with consecutive coils and use it to load an Yb magneto-optical trap (MOTs). Cooling efficiency is measured by the fluorescence intensity of the atomic cloud trapped by the MOT. An optimized magnetic field profile can acquire the maximum cooling efficiency, corresponding to a good compromise between the smaller magnetic field mismatch and the high capture velocity. Our studies provide useful information on how the performance of the Zeeman slower can be improved.

In accordance with nonperturbative quantum scattering theory, we investigate photoelectron angular distributions (PADs) from above-threshold detachment (ATD) of negative ions irradiated by circularly polarized few-cycle laser fields. Electrons ejected on the polarization plane demonstrate distinct anisotropies in angular distributions which distinctly vary with the carrier-envelope (CE) phase. The anisotropy is caused by interference between transition channels; it also depends strongly on laser frequency, pulse duration, and kinetic energy of photoelectrons. Optimal emission of photoelectrons, which varies with CE phase, makes it possible to control photoelectron motion.

Photoelectron angular distributions (PADs) from two-photon ionization of atoms in linearly polarized strong laser fields are obtained in accordance with the nonperturbative quantum scattering theory. We also study the influence of laser wavelength on PADs. For two-photon ionization very close to the ionization threshold, most of the ionized electrons are vertically ejected to the laser polarization. PADs from two-photon ionization of atoms are determined by the second order generalized phased Bessel function at which the ponderomotive parameter plays a key role. In terms of dependence of PADs on laser wavelength, corresponding variations for the ponderomotive parameter are demonstrated.

We focus on the full relativistic quantum mechanical calculations from boron to fluorine atoms with electronic configuration of 1s22s22pn (n = 1, 2, 3, 4, and 5), where 1s22s2 is the closed shell and 2pn is the open shell. Their active electrons in the open shell occupy all the six spinors as far as possible. Therefore, we suggest a new rule called “maximum probability” for the full symmetry group relativistic theory. Furthermore, the spectral fine structure of the atomic ground states based on the full relativistic theory and their intervals of L-S splitting are all reasonable. It is impossible to calculate the L-S splitting through non-relativistic quantum mechanics. The relativistic effect of atomic mass is increased significantly by about 12 folds from boron atom to fluorine atom.

We create a GaN photocathode based on graded AlxGa1?xN buffer layers to overcome the influence of buffer-emission layer interface on the photoemission of transmission-mode GaN photocathodes. A gate-shaped spectral response with a 260-nm starting wavelength and a 375-nm cut-off wavelength is obtained. Average quantum efficiency is 15% and short wavelength responses are almost equivalent to long wavelength ones. The fitted interface recombination velocity is 5×104 cm/s, with negligible magnitude, proving that the design of the graded buffer layers is efficient in obtaining good interface quality between the buffer and the emission layer.

We examine the saturation of relative current gain of In0.53Ga0.47As/InP single photon avalanche diodes (SPADs) operated in Geiger mode. The punch-through voltage and breakdown voltage of the SPADs can be measured using a simple and accurate method. The analysis method is temperature-independent and can be applied to most SPADs.

The coupling between guided optical waves in magneto-optic fiber Bragg gratings (MFBGs) with linear birefringence is investigated using the eigen-mode and coupled-mode approaches. The relationship between the polarization-dependent loss (PDL) and the eigen states of polarization (SOPs) in the MFBGs is discussed. Only the MFBGs with low linear birefringence are applied to the peak PDL-based magnetic field measurement, after which the linear dynamic range is determined using the relative magnitude of linear and magnetically induced circular birefringence. In this letter, a theoretical model is presented to explain the experimental results and help develop novel MFBG-based devices.

A new technique to generate 40-GHz carrier-suppressed return-to-zero (CSRZ) optical pulse trains using only a 10-GHz dual-parallel Mach-Zehnder modulator (MZM) is presented and experimentally demonstrated. The spectrum of the generated CSRZ pulses is calculated by simulation and compared with conventional MZM-based RZ and CSRZ pulse trains. The experimental results demonstrate that CSRZ pulse trains are obtained, and that the carrier and the unwanted 20-GHz low-frequency component are suppressed by 25 dB. The technique can also be extended to 160-GHz CSRZ pulse generation when 40-GHz devices are employed.

The performance of a novel all-optical sampling orthogonal frequency division multiplexing (OFDM) system is proposed and analyzed. Time delays and phase shifters are used to realize all optical forward/inverse discrete Fourier transform (DFT/IDFT). Different system configurations are tested and analyzed to optimize the performance, including the system capacity, modulation formats, DFT/IDFT constructions, and the width of the sample pulse. The 50- and 100-Gb/s real-time all-optical sampling (AOS) OFDM systems are investigated. All results are analyzed, and useful suggestions are offered for future high-speed applications.

Point pattern matching is an essential step in many image processing applications. This letter investigates the spectral approaches of point pattern matching, and presents a spectral feature matching algorithm based on kernel partial least squares (KPLS). Given the feature points of two images, we define position similarity matrices for the reference and sensed images, and extract the pattern vectors from the matrices using KPLS, which indicate the geometric distribution and the inner relationships of the feature points. Feature points matching are done using the bipartite graph matching method. Experiments conducted on both synthetic and real-world data demonstrate the robustness and invariance of the algorithm.

A joint clustering and classification approach is proposed. This approach exploits unlabeled data for efficient clustering, which is applied in the classification with support vector machine (SVM) in the case of small-size training samples. The proposed method requires no prior information on data labels, and yields better cluster structures. Through cluster assumption and the notions of support vectors, the most confident k cluster centers and data points near the cluster boundaries are labeled and used to train a reliable SVM classifier. Our method gains better estimation of data distributions and mitigates the unrepresentative problem of small-size training samples. The data set collected from Landsat Thematic Mapper (Landsat TM-5) validates the effectiveness of the proposed approach.

Many remote sensing image classifiers are limited in their ability to combine spectral features with spatial features. Multi-kernel classifiers, however, are capable of integrating spectral features with spatial or structural features using multiple kernels and summing them for final outputs. Using a support vector machine (SVM) as classifier, different multi-kernel classifiers are constructed and tested using 64-band Operational Modular Imaging Spectrometer II hyperspectral image of Changping Area, Beijing City. Results show that by integrating spectral and wavelet texture information, multi-kernel SVM classifiers can obtain more accurate classification results than sole-kernel SVM classifiers and cross-information SVM kernel classifiers. Moreover, when the multi-kernel SVM classifier is used, the combination of the first four principal components from principal component analysis and wavelet texture provides the highest accuracy (97.06%). Multi-kernel SVM is therefore an effective approach to improve the accuracy of hyperspectral image classification and to expand possibilities for remote sensing image interpretation and application.

An evaluation for objectively assessing the target detectability in night vision color fusion images is proposed. On the assumption that target detectability could be modeled as the perceptual color variation between the target and its optimal sensitive background region, we propose an objective target detectability metric in CIELAB color space defined by four color information features: target luminance, region perceptual luminance variation in human vision system, region hue difference, and region chroma difference. Experimental results show that this proposed metric is perceptually meaningful because it corresponds well with subjective evaluation.

A concave two-dimensional (2D) photonic crystal waveguide (PCW) with corrugated surface is theoretically used as a focusing structure. To design this structure, a genetic algorithm is combined with the finite-difference time-domain method. For PCWs with different degrees of concaveness, the power reaches about 80% at different focusing points when the morphology of the concave surface is optimized. More importantly, the focusing location is easily controlled by changing the location of the detector placed in the output field.

To increase the photoelectronic conversion efficiency of the single discharge tube and to meet the requirements of the laser cutting system, optimization of the discharge tube structure and gas flow field is necessary. We present a computational fluid dynamic model to predict the gas flow characteristics of high-power fast-axial flow CO2 laser. A set of differential equations is used to describe the operation of the laser. Gas flow characteristics, are calculated. The effects of gas velocity and turbulence intensity on discharge stability are studied. Computational results are compared with experimental values, and a good agreement is observed. The method presented and the results obtained can make the design process more efficient.

A model of an annular flat-topped vortex beam based on multi-Gaussian superimposition is proposed. We experimentally produce this beam with a computer-generated hologram (CGH) displayed on a spatial light modulator (SLM). The power of the beam is concentrated on a single-ring structure and has an extremely strong radial intensity gradient. This beam facilitates various applications ranging from Sisyphus atom cooling to micro-particle trapping.

Generally, Ag and N can be taken as relatively better candidates for p-type ZnO. In this letter, we investigate the electronic structures and optical properties of N- or Ag-doped ZnO with F as the reactive donor. F atom is found to not only enhance acceptor solubilities, but also lower acceptor levels in the band gap of co-doped ZnO. In addition, we analyze the imaginary portion of the dielectric functions, refractive indices, and loss functions for pure and co-doped ZnO. A comparison with pure ZnO shows that the remarkable feature for these co-doped ZnO is a strong absorption in the visible light region, indicating that they could be taken as the potential candidates for photocatalytic material.

The temperature-dependent photoluminescence (PL) spectra of BaIn2O4, prepared by coprecipitation, are measured and discussed. Aside from the reported 3.02-eV violet emission, the 1.81-eV yellow emission involved with oxygen vacancy is also observed at room temperature wherein the deep donor level is at 1.2 eV. With the temperature increasing, the peak energies for both emissions show a red shift. Moreover, the yellow emission intensity decreases while the violet emission intensity increases. The temperature dependence of the yellow emission intensity fits very well into the one-step quenching process equation, indicating a fitted activation energy at 19.2 meV.

By optimizing the phase matching condition of high harmonic generation (HHG) from a supersonic neon gas jet, the enhanced HHG in the region of 60?70 eV has been selected. Three-dimensional numerical calculation shows that plasma plays a significant role in the phase matching process of HHG in a supersonic gas jet with short medium length. Due to plasma formation, the harmonic emission decays as the laser intensity reaches over 3.5 ￡ 1014 W/cm2. The plasma induces the broadening and blue shift of the HHG spectra, which provides a method for fine-tuning the harmonic wavelength.

A novel tunable optical power splitter, with a Y-branch waveguide based on the total internal reflection and a microprism with tunable index refraction, is presented. Numerical simulation of its optical performance shows that a high dynamic range, low optical loss, and relatively low wavelength-dependence can be achieved. This component offers numerous advantages such as ease for fabrication, low cost, and compact size, which are very useful for potential application in integrated optical devices.

We apply phase retrieval method to align projection data for tomographic reconstruction in reflective tomography laser radar imaging. In our experiment, the target is placed on a spin table with an unknown, but fixed, axis. The oscillatory motion of the target in the incident direction of the laser pulse is added at each view to simulate the real satellites random motion. The experimental simulation results demonstrate the effectiveness of this method to improve image reconstruction quality. Future research also includes the development of projection registration based on phase retrieval for targets with more complicated structure.

A novel concept for an optical multilayer ultrasonic hydrophone with the sensing film deposited on a triangular pyramid glass substrate is proposed. Using the calculation model for the spectral coefficients’ derivatives of a dielectric multilayer optical coating, the acousto-optic sensitivity characteristic of the hydrophone is analyzed with different measurement laser polarizations and incident angles. We present a reasonable method and adjusting strategy for the optimum working point selection of the ultrasound measurement. Analytic results show that the novel hydrophone possesses all the other merits of a plate glass substrate optical multilayer hydrophone but with improved detection sensitivity. A longer measurement time without distortion decreases the difficulty of high frequency signal circuits. Spatial split of the ultrasound signal caused by the substrate’s triangular pyramid roof simplifies the spatial spot area correction, which contributes to the accurate calibration of the hydrophone’s wideband frequency response.

Ta2O5 and Nb2O5 films are deposited on BK7 glass substrates using an electron beam evaporation method and are annealed at 673 K in the air. In this letter, comparative studies of the optical transmittance, microstructure, chemical composition, optical absorption, and laser-induced damage threshold (LIDT) of the two films are conducted. Findings indicate that the substoichiometric defect is very harmful to the laser damage resistance of Ta2O5 and Nb2O5 films. The decrease of absorption improves the LIDT in films deposited by the same material. However, although the absorption of the Ta2O5 single layer is less than that of the Nb2O5 single layer, the LIDT of the former is lower than that of the latter. High-reflective (HR) coatings have a higher LIDT than single layers due to the thermal dissipation of the SiO2 layers and the decreased electric field intensity (EFI). In addition, the Nb2O5 HR coating achieves the highest LIDT at 25.6 J/cm2 in both single layers and HR coatings.

We propose a new optical profilometer for three-dimensional (3D) surface profile measurement in real time. The deviation angle is based on geometrical optics and is proportional to the apex angle of a test plate. Measuring the reflectivity of a parallelogram prism allows detection of the deviation angle when the beam is incident at the nearby critical angle. The reflectivity is inversely proportional to the deviation angle and proportional to the apex angle and surface height. We use a charge-coupled device (CCD) camera at the image plane to capture the reflectivity profile and obtain the 3D surface profile directly.