Nonlinear optical properties of [（CH3）4N]Au（dmit）2 using Z-scan technique

The third-order optical nonlinearities of [（CH3）4N]Au（dmit）2 （dmit = 4,5-dithiolate-1,3-dithiole-2-thione） at 532 nm and 1064 nm are investigated using the Z-scan technique with pulses of picoseconds duration. The Z-scan spectra reveal a strong nonlinear absorption （reverse saturable absorption） and a negative nonlinear refraction at 532 nm. No nonlinear absorption is observed at 1064 nm. The molecular second-order hyperpolarizability γ for the [（CH3）4N]Au（dmit）2 molecule at 532nm is estimated to be as high as （2.1 ±0.1） × 10^-31 esu, which is nearly three times larger than that at 1064 nm. The mechanism responsible for the difference between the results is analysed. Nonlinear transmission measurements suggest that this material has potential applications in optical limiting.

Frequency Stabilization of Pulsed Injection-Seeded OPO Based on Optical Heterodyne Technique

The resistance between any two lattice points in an infinite,centered-triangular lattice of equal resistors is determined using the lattice Green function method.It is shown that the two-point resistance on the centeredtriangular lattice is expressed in terms of the resistance of a triangular lattice.Some exact values for the resistance near the origin of the lattice are presented.For large separation between lattice points the asymptotic forms of the resistance are calculated.

Effects of heat treatment on morphological,optical and electrical properties of ITO films by sol-gel technique

Indium-tin-oxide(ITO)films were prepared on the quarts glass by sol-gel technique.Effects of different heat treatment temperatures and cooling methods on the morphological,optical and electrical properties of ITO films were measured by TG/DTA, IR,XRD,SEM,UV-VIS spectrometer and four-probe apparatus.It is found that the crystallized ITO films exhibit a polycrystalline cubic bixbyite structure.The heat treatment process has significant effects on the morphological,optical and electrical properties of ITO films.Elevating the heat treatment temperature can perfect the crystallization process of ITO films,therefore the optical and electrical properties of ITO films are improved.But the further increasing of heat treatment temperature results in the increment of ITO films’resistivity.Compared with ITO films elaborated by furnace cooling,those prepared through air cooling have following characteristics as obviously decreased crystalline size,deeply declined porosity,more compact micro-morphology,improved electrical property and slightly decreased optical transmission.

The Diagnosis of Plasma Parameters in Surface Alloying Technique by Optical Emission Spectrometry

Electron density （Ne） in a glow discharge plasma for the surface alloying technique is diagnosed by optical emission spectrometry （OES）. With CH4 as the feeding gas, Ne is obtained by comparing the Hβ spectrum according to the Stark broadening effect. It is noticed that Ne varies with the working pressures （30 Pa to 70 Pa） and cathode voltages （500 V to 1000 V）, respectively. Due to an abnormal glow discharge, Ne is between 1. 71 × 10^15 /cm^3 to 6.64 × 10^15 /cm^3 and increases rapidly with working gas pressures and cathode voltages. The results show that OES is a useful method to measure the plasma parameters in a surface alloying glow discharge plasma.

Optical nonlinearity measurement of 4-(N-methyl,N-hydroxyethl)amino,4'-nitroazobenzene using a transmittance technique with a phase object(T-PO) with top-hat beams at 600-nm wavelength

The transmittance technique with a phase object（T-PO）,for measuring optical nonlinear coefficients is proposed with a top-hat beam.The sensitivity of the T-PO with a top-hat beam is a factor of 4 greater than that with a Gaussian beam.The validity of this method is verified by measuring the nonlinearity of a well-characterized liquid,CS 2 at 532-nm wavelength.The ease of use of this method has been proved by measuring a new compound 4-（N-methyl,N-hydroxyethyl）amino,4＇-nitroazobenzene（ANAB） at 600-nm wavelength,indicating that this method can be extended to the measurement of optical nonlinearities in a wide-band spectrum.

Multidither coherent optical adaptive technique for deep tissue two-photon microscopy

Two-photon microscopy normally suffers from the scattering of the tissue in biological imaging.Multidither coberent optical adaptive technique(COAT)can correct the scattered wavefront in parallel.However,the determination of the corrective phases may not be completely accurate using conventional method,which undermines the performance of this technique.In this paper,we theoretically demonstrate a method that can obtain more accurate corrective phases by determining the phase values from the square root of the fuorescence signal.A numnerical simulation model is established to study the performance of adaptive optics in two-photon micros-copy by combining scalar diffraction theory with vector diffraction theory.The results show that the distortion of the wavefront can be corrected more thoroughly with our method in two-photon imaging.In our simulation,with the scattering from a 450-mn-thick mouse brain tissue,excitation focal spots with higher peak-to background ratio(PBR)and images with higher contrast can be obtained.Hence,further enhancement of the multidither COAT correction performance in two-photon imaging can be expected.

Editorial: Advances in Optical Techniques for Mechanical Measurements

Recently, optical techniques have attracted great attention due to their excellent non-destructive, non-contact, high-resolution, and full-field characteristics. Applications can be found in diverse fields such as precision mechanics and manufacturing, aerospace and automotive testing and inspection, materials science, and biomedical engineering. Advances in Optical Techniques for Me- chanical Measurements presents the latest research progresses in several widely used optical techniques with applications in preci- sion mechanical engineering.

Numerical Controlled Processing Techniques for Optical Components

Comparied to traditional optical processing methods,numerical controlled surfacing techniques have irreplaceable effects especially in spherical and aspherical optics. In this paper,fabricating methods,mechanisms and processes are analyzed. Also,some processing difficulties and problems are discussed. The possible improvements and feasible methods are given.

Multiplexing Technique Applied in the Optically Powered Oil-tank Detection System

The method of using multiplexing technique to realize the optically powered multiple detection system is presented. As this system adopted novel time and pulse width multiplexing techniques, reliable separation and error code correcting techniques, it realizes optically powered multiple channel and parameters detection, and successfully applied in the oil tanks for temperature, pressure, liquid level and reserve measurings.

Performance Analysis of Optical Wireless Communication System Employing Neuro-Fuzzy Based Spot-Diffusing Techniques

The spot-diffusing technique provides better performance compared to conventional diffuse system for indoor optical-wireless communication (OWC) system. In this paper, the performance of an OW spot-diffusing communication system using Neuro-Fuzzy (NF) adaptive multi-beam transmitter configuration has been proposed. The multi-beam transmitter generates multiple spots pointed in different directions, hence, forming a matrix of diffusing spots based on position of the receiver and receiver mobility. Regardless of the position of the transmitter and receiver, NF controller target the spots adaptively at the best locations and allocates optimal power to the spots and beam angle are adapted in order to achieve better signal-to-noise plus interference ratio (SNIR). Maximum ratio combining (MRC) is used in the imaging receiver. The proposed OW spot-diffusing communication system is compared with other spot-beam diffusion methods proposed in literature. Performance evaluation revels that the proposed NF based OW spot-diffusing communication system outperforms other spot-beam diffusion methods.

A low-cost and high-performance technique for adaptive optics static wavefront correction

Non-Common Path Error(NCPE) is one of the factors that limit an Adaptive Optics(AO)system from delivering ultra-high performance. To correct the NCPE associated static aberration, we propose a simple but robust and high-performance pupil-plane based wavefront measurement and correction technique, which can copy a single-mode fiber generated perfect wavefront to the AO system via an iteration optimization process, and the NCPE can be effectively corrected by directly commanding the Deformable Mirror(DM) of the AO system. Compared with the previous focal-plane based approach that uses focal plane based Point Spread Function(PSF) for correction evaluation, the pupil-plane based approach can be reliably and rapidly converged to a global optimization result and provides better performance, in particular for an AO system with a large initial static wavefront error. This technique we proposed can be implemented in astronomical AO systems where extremely high performance is required.

Intercomparison of NO_x, SO_2, O_3, and Aromatic Hydrocarbons Measured by a Commercial DOAS System and Traditional Point Monitoring Techniques

A field-based Intercomparison study of a commercial Differential Optical Absorption Spectroscopy (DOAS) instrument (OPSIS AB, Sweden) and different point-sample monitoring techniques (PM, based on an air monitoring station, an air monitoring vehicle, and various chemical methods) was conducted in Beijing from October 1999 to January 2000. The mixing ratios of six trace gases including NO, NO2, SO2, O3, benzene, and toluene were monitored continuously during the four months. A good agreement between the DOAS and PM data was found for NO2 and SO2. However, the concentrations of benzene, toluene, and NO obtained by DOAS were significantly lower than those measured by the point monitors. The ozone levels monitored by the DOAS were generally higher than those measured by point monitors. These results may be attributed to a strong vertical gradient of the NO-O3-NO2 system and of the aromatics at the measurement site. Since the exact data evaluation algorithm is not revealed by the manufacturer of the DOAS system, the error in the DOAS analysis can also not be excluded.

Preparation, characterization and nonlinear optical properties of colloidal gallium arsenide nanocrystals

GaAs nanocrystals were prepared via a simple mechanical ball milling technique. The prepared GaAs nanocrystals have high purity and could form colloidal ethanol suspension without any surfactant additives. The colloidal GaAs nanocrystal suspension displayed excellent two-photon absorption property over the visible and near-infrared region from 490 nm to 1064 nm, which enables it to become a promising broadband optical limiting material.

Extending a release-and-recapture scheme to single atom optical tweezer for effective temperature evaluation

By recording the fluorescence fraction of the cold atoms remaining in the magneto-optical trap （MOT） as a function of the release time, the release-and-recapture （R＆R） method is utilized to evaluate the effective temperature of the cold atomic ensemble. We prepare a single atom in a large-magnetic-gradient MOT and then transfer the trapped single atom into a 1064-nm microscopic optical tweezer. The energy of the single atom trapped in the tweezer is further reduced by polarization gradient cooling （PGC） and the effective temperature is evaluated by extending the R-R technique to a single atom tweezer. The typical effective temperature of a single atom in the tweezer is improved from about 105 μK to about 17 μK by applying the optimum PGC phase.

A new distribution scheme of decryption keys used in optical verification system with multiple-wavelength information

A new distribution scheme of decryption keys used in optical verification systems is proposed. The encryption procedure is digitally implemented with the use of an iteration algorithm in computer. Three target images corresponding to three wavelengths are encoded into three sets of phase-only masks （POMs） by a special distributing method. These three sets of POMs are assigned to three authorized users as the personal identification. A lensless optical system is used as the verification system. In the verification procedure, every two of the three authorized users can pass the verification procedure cooperatively, but only one user cannot do. Numerical simulation shows that the proposed distribution scheme of decryption keys not only can improve the security level of verification system, but also can bring convenience and flexibility for authorized users.

Sub-nanosecond optical switch based on silicon racetrack resonator

We experimentally demonstrate a small-size and high-speed silicon optical switch based on the free carrier plasma dispersion in silicon. Using an embedded racetrack resonator with a quality factor of 7400, the optical switch shows an extinction ratio exceeding 13 dB with a footprint of only 2.2 × 10-3 mm^2. Moreover, a novel pre-emphasis technique is introduced to improve the optical response performance and the rise and the fall times are reduced down to 0.24 ns and 0.42 ns respectively, which are 25% and 44% lower than those without the pre-emphasis.

New decomposition of the Fresnel operator corresponding to the optical transformation in ABCD-systems

By virtue of the coherent state representation of the newly introduced Fresnel operator and its group product property we obtain new decomposition of the Fresnel operator as the product of the quadratic phase operator, the squeezing operator, and the fractional Fourier transformation operator, which in turn sheds light on the matrix optics design of ABCD-systems The new decomposition for the two-mode Fresnel operator is also obtained by the use of entangled state representation.

Structural and Optical Dispersion Characterisation of Sprayed Nickel Oxide Thin Films

Crystalline and non-crystalline nickel oxide (NiO) thin films were obtained by spray pyrolysis technique (SPT) using nickel acetate tetrahydrate solutions onto glass substrates at different temperatures from 225 to 350℃. Structure of the as-deposited NiO thin films have been examined by X-ray diffraction (XRD) and atomic force microscope (AFM). The results showed that an amorphous structure of the films at low substrate temperature (Ts = 225℃), while at higher Ts ≥ 275℃, a cubic single phase structure of NiO film is formed. The refractive index (n) and the extinction coefficient (k) have been calculated from the corrected transmittance and reflectance measurements over the spectral range from 250 to 2400 nm. Some of the optical absorption parameters, such as optical dispersion energies, Eo and Ed, dielectric constant, ε, the average values of oscillator strength, So, wavelength of single oscillator λo and plasma frequency, ωp, have been evaluated.

An Improved Optical Flow Method for Image Registration with Large-scale Movements

在这份报纸，为图象登记的一个改进光流动方法被建议。它以它与一个起始的运动评估者改进光流动方法的方法是新奇的：扩大了阶段关联技术(EPCT ) ，用补偿前者的缺乏的后者的优点。以一种更多的详细方式，光流动方法能到达亚象素精确性并且计算象啁啾并且倾斜一样的复杂失真模式，这能被说但是与大规模运动弱。因为 EPCT 用象素水平精确性盖住大翻译和旋转的大小并且在精明的负担是有效的，它能为光流动方法被当作一个好起始的运动评估者。测试证明了特别，这个改进方法将显著地与大规模运动为图象提高登记表演并且对随机的噪音柔韧。