The seasonal variability of cirrus depolarization ratio and its altitude at the region of Beijing (39.93°N,116.43°E, the capital of China) are presented. From the results obtained from the cloud aerosol lidar and infrared pathfinder satellite observations lidar measurements, it appears that the values of depolarization ratio and altitude of cirrus are generally higher in autumn and summer than those in spring and winter, and the cirrus altitude is modulated by the height of tropopause. Additionally, the depolarization ratio tends to linearly vary with the increase of altitude and the decrease of temperature.

The laser-induced fluorescence (LIF) characteristic of plant is directly linked to the photosynthesis. The LIF lidar for remote monitoring of plant has been suggested as one of the useful tools to identify plant species and determine its physiological status for a long time. So recently a LIF lidar for remote sensing of plant in Anhui Institute of Optics and Fine Mechanics is developed. It transmits laser beam at wavelength of 354.7 and 532 nm, and receives elastic echo and fluorescence echo at wavelength of 680 and 740 nm. Numerical simulations are carried out to determine achievable lidar performance including operation range. Validity of fluorescence signal is certified and then some results are presented. Comparison of the fluorescence characteristic among birch, conifer, and algae show that the °uorescence lidar is one of the potential tools to differentiate plant species.

The square soft-edge diaphragm with round angle is designed by Matlab, and is sent to a liquid crystal spatial light modulator by the computer. In order to obtain precompensation for the following laser system, local diaphragm transmission can be adjusted by feedback signals of surface-channel charge-coupled device (SCCD). This method can reduce the diffraction effect and realize no modulation, high stability, high homogeneity, and large scale laser beam. Several parameters of soft-edge diaphragms which affect the laser beam quality are studied systematically, and the optimized values are obtained. The method can avoid the serious modulation of hard edges and provide soft-edge diaphragms of different shapes in a fast and convenient way for the large scale laser beam system.

A novel approach to generate and distribute ultra-wideband (UWB) pulses in optical domain is investigated. In this proposed scheme, a dual-electrode Mach-Zehnder modulator (DE-MZM) is biased at its quadrature point so as to realize the linear response. Then the intensity of output optical field can be assumed to the subtraction of two input Gaussian pulses. If the input Gaussian pulses are with the same sharp parameters but different time delays, a quasi-monocycle-waveform UWB signal can be generated. If the input Gaussian pulses are with different amplitudes and full-width at half-maximum (FWHM), a quasi-doublet-waveform UWB signal can be generated. A transmission of the UWB signals through a 25-km single mode fiber is carried out successfully. The results in both temporal and frequency domains are also presented.

Current generalized multi-protocol label switching (GMPLS) standards do not include adequate models for wavelength-switched optical networks (WSON) in recovery mechanisms. In this letter, GMPLS/path computation element (PCE) extensions are applied for the restoration of the lightpaths disrupted by collision or optical impairment. A reserved de°ection routing scheme is proposed to achieve fast restoration. It uses the expanded PCE component to compute and assign the backup paths for lightpath recovery. Numerical results demonstrate that this scheme is effective and low cost.

By analyzing the error distribution rule of the boundary recursive reconstruction algorithm in controlled micro-scanning, a sub-pixel image processing algorithm is proposed to reduce the error. The gray statistical principle is used in the algorithm to optimize the error and acquire the sub-pixel image that approximates the original image. The simulation result shows that the e?ect of this algorithm is better than the over-sample and simple boundary recursive algorithm (BRA), and it results in a good effect both in those of visible light and infrared imaging systems. Therefore, the application of this algorithm will enhance the performance of optoelectronic imaging systems.

Huge computational complexity of multiview video plus depth (MVD) coding is an obstacle for putting MVD into applications. A fast macroblock mode selection algorithm is proposed to reduce the computational complexity of multiview depth video coding. The proposed algorithm, implementing on a joint coding scheme, combines an effective prediction mechanism and an object boundary discriminating method. The prediction mechanism which is designed based on the macroblock mode similarities reduces the number of macroblock mode candidates in depth video coding. The object boundary discriminating method extracts the regions, which are with discontinuous depth values and important for virtual view rendering, by using macroblock deviation factor. Experimental results show that the proposed algorithm can significantly promote the coding speed of depth video by 2.00-3.40 times, while maintaining high rate distortion (RD) performance in comparison with the full search algorithm.

A new performance metric, the two-dimensional (2D) contrast threshold surface, is proposed to characterize the systematic performance of a multi-spectral imaging sensor. Specifically, how to measure this performance metric is presented based on the discriminations of a set of sine-wave test patterns with different radiance magnitudes and spectral properties. The theoretical model for predicting the 2D contrast threshold surface is derived based on an analytical description of the effective contrast between the test pattern and its background, in which the impacts of fusion algorithms on the 2D contrast threshold surface are also discussed using the minimum threshold match criteria. Preliminary simulation results show that this model can be used to quantitatively characterize the real influence of the spectral di?erences and spatial frequencies on the contrast thresholds required for the observer to just resolve the images of the test patterns through a multi-spectral imaging sensor.

Wavefront coding (WFC) is used to extend the field depth of an incoherent optical system by employing a phase mask on the pupil. We uses a Fisher information (FI) metric based optimization method to design a phase mask by taking the modulation transfer function (MTF) of the practical optical system into consideration. This method can modulate the wavefront so that the point spread function and optical transfer function are insensitive to the object distance. The simulation results show that the optimized phase mask based on the proposed method can further improve the defocusing image quality while maintaining the focusing image quality.

Principles of terahertz (THz) interferometric synthetic aperture imaging with heterodyne and optical techniques are presented. A THz interferometric experiment based on optical up-conversion is set up. The received THz signal is modulated into an optical carrier and transmitted in a fiber. To simulate phase differences between two THz receivers, the output of receiver is divided and a phase shifter is placed before electro-optical modulation (EOM). Interferometric spectra of these modulated optical signals are examined at different phase shifts. Otherwise, carrier suppression and phase error calibration are discussed for THz interferometric synthetic aperture imaging.

We demonstrate the subsurface imaging of an articular cartilage using Fourier-domain common-path optical coherence tomography. The bare fiber probe integrated with a hypodermic needle provides the rigidness required to perform lateral scanning with less microscale bending. By submerging both the probe and the specimen into saline solution, we not only reduce the beam divergence, but also increase the signal-to-noise ratio compared with the measurement in free space. Our system can di?erentiate the characteristic cartilage zones and identity various micro-structured defects in an ex vivo chicken knee cartilage, thus demonstrating that it could be used to conduct early arthritis diagnosis and intraoperative endo-microscopy.

The Brownian motion of a polystyrene bead trapped in a time-sharing optical tweezers (TSOT) is numerically simulated by adopting Monte-Carlo technique. By analyzing the Brownian motion signal, the effective stiffness of a TSOT is acquired at different switching frequencies. Simulation results confirm that for a specific laser power and duty ratio, the effective stiffness varies with the frequency at low frequency range, while at high frequency range it keeps constant. Our results reveal that the switching frequency can be used to control the stability of time-sharing optical tweezers in a range.

Accurate measurement of the optical properties of biological tissue is very important for optical diagnosis and therapeutics. An artificial neural network (ANN)-based inverse reconstruction method is introduced to determine the optical properties of turbid media, which is based on the reflectance (R) and transmittance (T) of a thin sample measured by a double-integrating-spheres system. The accuracy and robustness of the method has been validated, and the results show that the root mean square errors (RMSEs) of the absorption coefficient \mu a and scattering coefficient \mu′ s reconstruction are less than 0.01 cm^-1 and 0.02 cm^-1, respectively. The algorithm is not only very accurate in the case of a lower albedo (~0.33), but also very robust to the noise of R and T especially for the \mu′ s reconstruction.

The self-mixing interferometer is used to investigate the characteristics of resonant frequency of the microresonator, which is excited by a sinusoidally driven loud-speaker. The detected self-mixing signal is processed by the phase reconstruction method. The 1st-order resonant frequency of the microresonator is measured to be 4.437 kHz with full-width at half-maximum (FWHM) of 0.13 kHz. The measurement results are verified by the sinusoidal phase modulating (SPM) interferometer.

Integrated scatterometer for qualification of superpolished substrates for laser-gyro by surface scatter loss measurement is constructed. Different from the qualification of substrate by surface roughness, the scatterometer measures the forward surface scatter loss to check whether the mirror made of the substrate will be suitable for the required laser-gyro lock-in specification. The scatterometer utilizes convex lens instead of integrating sphere to collect scatter light. Special sample support and baffle are designed to block unwanted light. The result of stability test is given, which is about 0.4% over 10 h.

A new method to obtain linear polarization operation by Brewster's angle-polished fiber end is demonstrated. By using the special polarization operation technique together with introducing a narrow-linewidth fiber grating into the laser cavity, a cladding-pumped linear polarization and single-transverse-mode (M²<1.1) Yb-doped fiber laser with narrow linewidth whose full-width at half-maximm (FWHM) is less than 0.2 nm, is obtained in a simple configuration. The output power is up to 10 W which is continuouswave output at 1085 nm, and the slope e±ciency is 63% with respect to the coupled pump power and 75% with respect to the absorbed pump power, respectively. The measured 21-dB polarization extinction ratio does not degrade with the output power. The simplicity of such an approach is highly beneficial for a number of applications, including the use of a fiber laser for the nonlinear wavelength conversion (especially for the intracavity frequency doubling) and for the coherent and spectral beam combination.

In diode pumped Nd:YAG lasers, the quantum defect is the most important parameter determining the thermal load of the laser crystal, which can be dramatically reduced by pumping directly into the upper laser level. A compact folded three-mirror cavity with a length of 105 mm is optimized to obtain a highly effcient 473-nm laser. When the absorbed pump power (with 15.8-W incident pump power) at 885 nm into Nd:YAG is 10 W, a continuous-wave 473-nm blue laser as high as 2.34 W is achieved by LBO intra-cavity frequency doubled. The optical-to-optical conversion effciency is 14.8%. To the best of our knowledge, this is the highest e±ciency at 473 nm by an intra-cavity doubled frequency Nd:YAG laser.

The energy transfer and cooperation upconversion processes are investigated in Yb³⁺/Er³⁺ codoped phosphate glass. Based on the measured curves of output power versus incident power, the laser and spectroscopic parameters of the glass are fitted and analyzed. We focus on the resonant energy transfer constant k from Yb³⁺ to Er³⁺ as well as the cooperation upconversion coe±cient C_up from ⁴I_13/2 of Er³⁺. The fitted k and C_up can give almost the same results for different thicknesses of glass disk with the same doping concentrations. The determination of these parameters is helpful for the development of Yb³⁺/Er³⁺codoped laser glass.

Two operating modes, independent self-mode-locking and cross-mode-locking, are presented in a two-beam-pumped double-cavity dual-wavelength femtosecond Ti:sapphire laser. Synchronization of femtosecond and picosecond laser pulses is achieved by properly adjusting the cavity length matching and distributing the pump laser powers in the two laser cavities, and moreover, a timing jitter of 517 fs between femtosecond and picosecond pulses is obtained, with wavelength tuning ranges around 36 and 22 nm in the femtosecond and picosecond cavities, respectively.

Optically transparent Er³⁺/Tm³⁺/Yb³⁺ tri-doped oxyfluoride tellurite based nano-crystallized glass ceramics with the batching composition of 73TeO₂-15ZnO-7ZnF₂-3YF₃-1.5YbF₃-0.3ErF₃-0.2TmF₃ (mol%) is prepared by a conventional melting quenching and the subsequent heat treatment processes. The sizes of grown nano-crystals in glass matrix appear to be smaller than 100 nm from the scanning electron microscope measurement. Visible up-conversion luminescence of the as melted glass and glass ceramics is investigated. The three-color up-conversion luminescence intensities by 980-nm pumping are increased significantly due to the heat treatment, and the blue intensity increases with a higher magnitude than other wavelengths after heat treatment.

YAG:Ce crystal with a diameter of 110 mm is successfully grown by the temperature gradient technique (TGT). The effects of annealing on the luminescence efficiency of YAG:Ce crystal are investigated, and the optimal annealing temperature and atmosphere are obtained. The mechanism of variation behavior of the luminescence efficiency of YAG:Ce under different annealing conditions is discussed and some details on the luminescence associated with color centers are analyzed.

We develop a high-speed tunable, quasi-continuous-wave laser source for frequency domain (FD) optical coherence tomography (OCT). The laser resonance is realized within a unidirectional all-fiber ring cavity consisting of a fiber coupler, two fiber isolators, a semiconductor optical amplifier (SOA), and a fiber Fabry-Perot tunable filter (FFP-TF) for frequency tuning. Light output from the coupler is further amplified and spectral shaped by a booster SOA terminated at both ends with two isolators. The developed laser source provides up to 8000 sweeps per second over a full-width wavelength tuning range of 120 nm at center wavelength of 1320 nm with an average power of 9 mW, yielding an axial resolution of 13.6 \mu m in air and a maximum sensitivity of about 112 dB for OCT imaging. The instantaneous linewidth is about 0.08 nm, enabling OCT imaging over an axial range of 3.4 mm in air. For optimization consideration based on this custom-built swept laser, experimental study on imaging quality relevant parameters of the swept laser with sine and ramp driving waveforms to the FFP-TF is conducted, and investigation of the swept laser on the cavity length is done. Implementing the laser source in our established swept source based OCT (SS-OCT) system, real-time structural imaging of biological tissue is demonstrated.

Time-domain diffuse optical tomography can efficiently reconstruct optical parameters which can be further applied in diagnosing early breast cancer. Nevertheless, the performances of reconstructed imaging are badly influenced by different Jacobian magnitudes of absorption coefficient and reduced scattering coefficient. With the introudction of a relative data type based on generalized pulse spectrum technique, an efficient Jacobian scaling method is proposed. The interrelated simulated validation is also revealed for the enhancing performances.

Bespalov-Talanov theory on small-scale self-focusing is extended to include medium loss for a divergent beam. Gain spectrum of small-scale perturbation is presented in integral form, and based on the derived equations we find that the cutoff spatial frequency for perturbation keeps a constant value. The larger the medium loss is, the smaller the fastest growing frequency and the maximum gain of perturbation with defined propagation distance are. For a given medium loss the maximum gain of perturbation becomes larger, while the fastest growing frequency becomes smaller as the propagation distance becomes longer. Furthermore, physical explanations for the appearance of these features are given.

Second harmonic generation (SHG) results from molecules which are polarized by an external electric field often provided by an intense laser beam. The polarizability depends on firstly the intrinsic structural properties of the substance and hence the second-order nonlinear susceptibility, and secondly the intensity and polarization direction of the incident light. The polarization characteristics of the beam are therefore of interest. In this letter, we discuss some considerations in SHG microscopy of collagen when the incoming beam is circularly polarized, and present some supporting results as well as a numerical analysis. We propose a quasi-crystal model of collagen microstructure in an effort to further our understanding on this protein.

A numerical model of optical parametric amplification (OPA) is introduced to investigate the impact of wavefront phase distortion of pump on the beam quality of signal. Numerical results show that the unidentical walk-off directions of the pump and the idler waves are the main factors leading to the transfer of wavefront phase distortions of the pump to the signal, and by reducing the angle between the two directions, the beam quality factor (M²) can be greatly decreased and hence the good beam quality of the signal can be maintained.

The applications of white light-emitting diodes (LEDs) have become more and more wide recently, while the low light-extraction e±ciency of white LED limits its development. In this letter, a new structure of multilayer phosphor package of white LED is proposed to improve the light-extraction efficiency. It is illustrated that the thickness of phosphor layer plays an important role in improving the light-extraction efficiency of LED. The light-extraction efficiency of LED is improved by double-layer or multi-layer phosphor package structures.

An optical waveguide interconnect mesh network scheme for parallel multiprocessor systems based on an electro-optical printed circuit board (EOPCB) with multimode polymer waveguide is proposed. The system consists of 2×2 processor element chips interconnected in a mesh network configuration. An additional layer with optical waveguide structure is embedded in a conventional printed circuit board to construct the EOPCB. Vertical cavity surface emitting laser (VCSEL)/positive intrinsic-negative (PIN) arrays are applied as the optical transmitters/receivers. Three 1×12 VCSEL/PIN parallel optical transmitting/receiving modules are used to provide 32 input/output optical channels required by the 2×2 chip-to-chip optical mesh interconnect system. The data rate in each optical channel is 3.125 Gbps and thus 10 Gbps parallel optical interconnect link for each direction of a chip is obtained. The optical signals from a processor element chip can be transmitted to another chip through optical waveguide interconnect embedded in the board. Thus the optical interconnect mesh network for parallel multiprocessor system can be implemented.

We study the non-classical properties of the single-mode electro-magnetic field resulting from the interaction of a \Xi-type three-level atom initially in the coherent state, such as squeezing properties and sub-Poisson statistics. We show that if there are more photons in the cavity, the squeezing will appear earlier and be stronger under the same state, but the sub-Poisson statistics will be weaker, while sub-Poisson statistics and squeezing are more pronounced after the selective atomic measurement.

The entanglement dynamics involving the so-called entanglement sudden death of atoms in two-photon Tavis-Cummings model is investigated. Various initial conditions that may have influences on the entanglement evolution of atoms, especially on the appearance of atomic entanglement sudden death, are studied. The appearance of entanglement sudden death is sensitive to the initial conditions of the whole system, i.e., the concrete type of atomic initial state, the photon number in the cavity field, and the dipole-dipole interaction between atoms. It is shown that the strong dipole-dipole interaction between atoms can weaken the atomic entanglement sudden death.

The action mode between Dy(III)(NR)₃ and herring sperm DNA is studied by ultraviolet-visible (UV-vis) and fluorescence spectra as well as electrochemistry. Double-reciprocal method studies show that the binding stoichiometry between Dy(III)(NR)₃ and DNA is 1:1, the binding constants at different temperatures are 1。15×10⁵ L/mol at 25 ℃ and 2.09×10⁵ L/mol at 35 ℃, and the corresponding thermodynamic parameters are \Delta_rH \mathrm m = 2.48×10⁴ J/mol, \Delta_rG \mathrm m =-2.34×10⁴ J/mol, \Delta_rSm=161.7 J/(mol·K); \Delta_rS \mathrm m is the driving force in this reaction. Combined with Scatchard method and melting method, the results suggest that the interaction mode between Dy(III)(NR)₃ and herring sperm DNA is intercalation fashion and groove fashion.

In order to improve the laser-induced damage threshold (LIDT) of the ZrO₂ film, the effect of polyvinyl pyrrolidone (PVP) with different average molecular weight on coatings is studied. The ZrO₂ sol is prepared by the hydrolysis of zirconium n-propoxide with acetylacetone as the chelating agent. The PVP (K16-18) is more suitable to obtain high LIDT coatings than other PVPs. The LIDT of the ZrO₂-PVP coatings is improved with the increase of the PVP (K16-18) content. When the PVP (K16-18) content is 2.4 wt.-%, the LIDT of the ZrO₂-PVP coatings is 43.5 J/cm² (1064 nm, 12 ns). The ZrO₂ sol and ZrO₂-PVP (K16-18) sol have the good stability in 3 months. The refractive indices of the ZrO₂-PVP coatings decrease with the increase of the PVP (K16-18) content.

With the evolution of a laser pulse in water, the formation of a nonlinear X wave during femtosecond filamentation is investigated based on numerical simulations. In particular, we analyze the far-field angularly resolved spectra obtained for different temporal portions of the ultrashort pulse during its propagation. Our result shows that the refocusing of ultrashort pulse leads to the formation of dynamic X wave which essentially manifests itself as conical emission.

We analyze the stability of linearly chirped Gaussian pulse stacking (LCGPS) in the laser plasma reaction (LPR) in the inertial confinement fusion (ICF) system. The LPR can be treated as the process that the stacked pulse is first intensity filtered and then induces the plasma due to the thermalization time of the plasma. We also examine the stability of LCGPS over the change of the thermalization time of the plasma, the timing delay, and the intensity attenuation of the stacked pulse in the LPR, and compare the results with those of none chirped Gaussian pulse stacking (NCGPS). Our results show that LCGPS is more stable than NCGPS.