Generation of Optical Vortex Using a Spiral Phase Plate Fabricated in Quartz by Direct Laser Writing and Inductively Coupled Plasma Etching

A simple, economical and reliable technique is proposed for fabricating a spiral phase plate （SPP） in a quartz substrate to generate optical vortex with a unit topological charge at the wavelengths of 632.8nm. The spiral phase plate is first formed in the photoresist by direct laser writing lithography and then transferred into the quartz substrate by inductively coupled plasma etching. The performance of the fabricated SPP is verified by using beam intensity distribution, which is in agreement with the theoretical calculation result. The interference measurement suggests that we have succeeded to generate optical vortex with a unit topological charge with the fabricated SPP.

The study of a new n/p tunnel recombination junction and its application in a-Si:H/μc-Si:H tandem solar cells

This paper reports that a double N layer （a-Si：H/μc-Si：H） is used to substitute the single microcrystalline silicon n layer （n-μc-Si：H） in n/p tunnel recombination junction between subcells in a-Si：H/μc-Si：H tandem solar cells. The electrical transport and optical properties of these tunnel recombination junctions are investigated by current voltage measurement and transmission measurement. The new n/p tunnel recombination junction shows a better ohmic contact. In addition, the n/p interface is exposed to the air to examine the effect of oxidation on the tunnel recombination junction performance. The open circuit voltage and FF of a-Si：H/μc-Si：H tandem solar cell are all improved and the current leakage of the subcells can be effectively prevented efficiently when the new n/p junction is implemented as tunnel recombination junction.

Properties of Fraunhofer Diffraction by an Annular Spiral Phase Plate for Sidelobe Suppression

A simple and accurate method for calculating the optimal width of an annular spiral phase plate （SPP） to generate optical vortices with sidelobe suppression is proposed. The sideloSes can he sharply suppressed when the ratio of inner and outer radii of an annular SPP is equal to that of the principal ring and the first sidelobe diffracted by a circular SPP with the same topological charge n. Moreover, the ratio of the inner and outer radii of the optimal annular SPP depends only on the topological charge n and is not affected by the incident wavelength or the size of the SPP.

Location algorithm for seal imprints on Chinese bank-checks based on region growing

The paper focuses on location of seal imprints on Chinese bank-checks based on region growing.Region growing method can be applied to searching and locating connection region in an image.A seal imprint,however,is generally composed of various connection regions which are unconnected to each other.In order to locate the seal imprint,these connection regions must be fused together.In the paper,an algorithm for locating seal imprints on Chinese bankchecks based on region growing is proposed, of which a fusion criterion for connection regions in a seal imprint is put forth based on the image feature of Chinese bankcheck,and a center-rays model is proposed to find the topological relationship between connection regions,for which externally-tangent rectangle of region is used as the mark of location of region.The location experiment is achieved with a false-acceptance rate of 7.1% and a false-rejection rate of 0% on Chinese bankcheck.

A study of ultrafast electron diffusion kinetics in ultrashort-pulse laser ablation of metals

Temperature dependence of the electron diffusion in metallic targets, where the electron-lectron collision is the dominant process, is investigated with the help of an extended two-temperature model. In sharp contrast to the low electron temperature case, where only the electron-phonon collisions are commonly considered, the electron diffusion process underlying the high electron temperatures evolves dramatically different in both temporal and spatial domains. Calculated results of the ablation yield at different pulse durations are presented for a copper plate impinged by ultrashort laser pulses with energy fluences ranging from 0.1 J/cm^2 to 10 J/cm^2. The excellent agreement between the simulation results and the experimental data indicates the significant role of electron-electron collisions in material ablations using intense ultrashort laser pulses.

Time-resolved shadowgraphs and morphology analyses of aluminum ablation with multiple femtosecond laser pulses

Aluminum ablation by multiple femtosecond laser pulses is investigated via time-resolved shadowgraphs and scanning electron microscope （SEM） images of the ablation spot. The spatial distribution of the ejected material and the radius of the shock wave generated during the ablation are found to vary with the increase in the number of pulses. In the initial two pulses, nearly concentric and semicircular stripes within the shock wave front are observed, unlike in subsequent pulses. Ablation by multiple femtosecond pulses exhibits different characteristics compared with the case induced by single femtosecond pulse because of the changes to the aluminum target surface induced by the preceding pulses.

OLED-on-silicon chip with new pixel circuit

A low power 640×480 OLED-on-silicon chip design that used in microdisplay was presented. A novel pixel circuit was proposed to meet the special requirement of OLED-on-silicon. The novel pixel consists of three transistors and one capacitor （3T 1C）. It has simple structure and can effectively reduce the current glitch generated during the AC driving from 55 pA to 7.5 pA, so that it can improve the precision of grayscale of display as well as extend the lifetime of （]）LED material. Except for the pixel array, low power row driver, column driver and other functional modules were also integrated on the chip. Several techniques were adopted to reduce the power consumption and frequency requirement of the chip. Finally, a 16×3×12 resolution chip was fabricated with standard 0.35 μm CMOS process of CSM and the chip can operate correctly.

Bragg Gratings Written in Photonic Crystal Fibres with a High-Index Germanosilicate Core

Bragg gratings are straightforwardly written into a l O-ring photonic crystal fibre （PCF） with a highly Ge^3＋-doped core by means of a 193nm ArF excimer laser. The grating inscription efficiency is improved, due to enhanced photosensitivity and the large overlap between the fundamental mode and the photosensitive core. The exposure duration only lasts less than 180s. In addition, the high-index core changes the modai properties of the PCF and two groups of higher order mode resonance dips are therefore obtained. A strong cladding mode resonance is observed, because the LP02-1ike mode has a large overlap integral with the fundamental mode.

Highly Stable CdSe/CdS/ZnS Fluorophores in Acidic Environment:Acile Preparation and Modification of Core/shell/shell Nanocrystals

We described a facile method for preparing CdSe/CdS/ZnS core/shell/shell nanocrystals from air-stable single source precursors.The single source precursors of cadmium ethylxanthate and zinc ethylxanthate were used to form CdS and ZnS shell layers in octadecene.An efficient modification of CdSe/CdS/ZnS nanocrystals was subsequently performed to obtain hydrophilic nanocrystal fluorophores with good stability in a pH range of 1.6—10.

Examination of Validity of Paraxial Approximation in Second Harmonic Generation Microscopy under Low Numerical Aperture

By using a vectorial approach, the validity of paraxial approximation in second harmonic generation （SHG） microscopy under low numerical aperture （NA） is examined when the sample is a collagen fibril. Due to the larger value of dzzz and tensorial nature of SHG, the component Ez of the focused fieM may have strong effect on the radiation pattern of SHG. Numerical results indicate that when the value of NA exceeds 0.3, the effect of Ez can not be neglected, which results in the invalidation of paraxial approximation in SHG microscopy despite the fact that SHG microscopy is still under low NA focusing.

Fibre Bragg Gratings Inscribed in Homemade Microstructured Fibres

Fibre Bragg gratings （FBGs） are inscribed in homemade microstructured fibres by the standard phase mask method. Enhanced couplings between the forward fundamental mode and backward cladding modes are obtained. The mode coupling and spectral characteristics are investigated experimentally. The cladding mode resonances can be affected by filling active materials into the air holes, which will be useful for the implementation of tunable photonic devices in optical fibre communication and sensing systems.

Terahertz Metamaterial Sensor Based on Electromagnetically Induced Transparency Effect

A terahertz metamaterial sensor adopting the metamaterial-based electromagnetically induced transparency（EIT） effect is presented for determining the 1,4-dioxane concentration in its aqueous solution. The metamaterial sensor, which consists of an EIT element unit with a cut-wire metallic resonator and two split-ring metallic resonators fabricated on a 490-μm thick silicon substrate, operates in a transmission geometry. The EIT peak was red-shifted and decreased with the increase of the water volume. A maximum redshift about 54 GHz of the EIT peak was detected between the 1,4-dioxane and water. The presented linear behavior and high sensitivity of the EIT peak depending on the water concentration pave a novel avenue for sensor applications.

Flexible Cu（In, Ga）Se2 Thin-Film Solar Cells on Polyimide Substrate by Low-Temperature Deposition Process

The electrical and structural properties of polycrystalline Cu（In, Ga）Se2 films grown on polyimide （PI） substrates below 400℃ via one-stage and three-stage co-evaporation process have been investigated by x-ray diffraction spectra （XRD）, scanning electron microscopy （SEM） and Hall effect measurement. As shown by XRD spectra, the stoichiometric CIGS films obtained by one-stage process exhibit the characteristic diffraction peaks of the （In0.68Ga0.32）2Se3 and Cu（In0.7Ga0.3）2Se. It is also found that the film structures indicate more columnar and compact than the three-stage process films from SEM images. The stoichiometric CIGS films obtained by three-stage process exhibit the coexistence of the secondary phase of （In0.68Ga0.32）2Se3, Cu2-xSe and Cu（In0.7Ga0.3）2Se. High net carrier concentration and sheet conductivity are also observed for this kind of film, related to the presence of Cu2-xSe phase. As a result, when the CIGS film growth temperature is below 400℃, the three-stage process is inefficient for solar cells. By using the one-stage co-evaporation process, the flexible CIGS solar cell on a PI substrate with the best conversion efficiency of 6.38% is demonstrated （active area 0.16cm^2）.

Fabrication of Long-Period Fibre Gratings Using 800 nm Femtosecond Laser Pulses

Long-period fibre gratings inside standard single-mode optical communication fibres are successfully fabricated with infrared femtosecond laser pulses. The refractive index perturbations are well confined within the fibre core by choosing the proper laser focusing parameters and translation speed of the fibre during the direct laser writing process. With the self-focusing effect considered and at a constant average irradiation dose of 1.62 × 10^3 J/（cm^2μm）, the threshold intensity for fabricating long-period gratings with infrared femtosecond laser pulses is determined to be 5.13 × 10^13 W/cm2.

Characteristics and New Measurement Method of NCSFs of Individual Color Mechanisms of Human Vision

We propose a new method for determining neural contrast sensitivity functions （NCSFs） of isolated color mechanisms based on the measurements of wave-front aberrations and isoluminant color contrast sensitivity functions （CSFs）. Compared with the traditional method, this technique avoids the coherent noise and speckle noise, which are brought by the interference of laser beams, and has great flexibility for the measurements of NCSF of different color mechanisms. Our experiments indicate that the mean NCSF and CSF of the red mechanism are higher than those of the green mechanism, respectively, while those of the blue mechanism are the lowest. However the relative heights of the peak of NCSF and CSF between red and green mechanisms vary in subjects. There are some individuals whose peak values of NCSF and/or CSF of green mechanism are higher than that of the red mechanism. The NCSFs and CSFs of isolated color mechanisms all exhibit the similar characteristics and variation tendency. With the statistical average, the NCSFs of the red, green and blue mechanisms are higher than the corresponding CSFs in the whole spatial frequency. Compared with the corresponding CSFs curves, the peaks of the NCSFs of isolated color mechanisms shift toward higher spatial frequencies, especially for that of blue mechanism which has a largest shift of 3.9 c/deg.

Analysis of second-harmonic generation microscopy under refractive index mismatch

On the basis of the vector diffraction theory and Green＇s function method, this paper investigates the effects of refractive index mismatch on second-harmonic generation （SHG） microscopy. The polarization distribution and SHG intensity are calculated as functions of the sample radius and probe depth. The numerical results show that refractive index mismatch can result in peak intensity degradation, increase secondary lobes and extension of second- harmonic polarization distribution. Because of the attenuation of polarization intensity, the detected SHG intensity significantly decreases with increasing probe depth, which can limit the imaging depth of SHG microscopy inside thick samples. Forward SHG intensity decays slowly than backward SHG, due to the combination of extension second-harmonic polarization distribution and strong dependency of forward SHG on sample radius.

Effects of annealing rate and morphology of sol–gel derived ZnO on the performance of inverted polymer solar cells

The effects of annealing rate and morphology of sol–gel derived zinc oxide （ZnO） thin films on the performance of inverted polymer solar cells （IPSCs） are investigated. ZnO films with different morphologies are prepared at different annealing rates and used as the electron transport layers in IPSCs. The undulating morphologies of ZnO films fabricated at annealing rates of 10 ℃/min and 3 ℃/min each possess a rougher surface than that of the ZnO film fabricated at a fast annealing rate of 50 ℃/min. The ZnO films are characterized by atomic force microscopy （AFM）, optical transmittance measurements, and simulation. The results indicate that the ZnO film formed at 3 ℃/min possesses a good-quality contact area with the active layer. Combined with a moderate light-scattering, the resulting device shows a 16% improvement in power conversion efficiency compared with that of the rapidly annealed ZnO film device.

Reduction of the phosphorus contamination for plasma deposition of p-i-n microcrystalline silicon solar cells in a single chamber

This paper investigates several pretreatment techniques used to reduce the phosphorus contamination between solar cells. They include hydrogen plasma pretreatment, deposition of a p-type doped layer, i-a-Si：H or μc-Si：H covering layer between solar cells. Their effectiveness for the pretreatment is evaluated by means of phosphorus concentration in films, the dark conductivity of p-layer properties and cell performance.

In-situ growth of Ca/P salt on Ti surface induced by femtosecond lasers in hydroxyapatite suspension

Pure Ti plate surfaces are micro-ablated by femtosecond lasers in the ambience of hydroxyapatite suspension. It is found that three-stage hierarchical surface structures are produced with various laser energies. When the laser energy is 150μJ, a lava-like structure with a distribution of nanoholes is dispersed evenly on the laser ablated surface. While in the case of 300 μJ, the grooves-and-islands micro-patterns covered with nanoparticles are generated on the surface. Remarkably, Ca/P based substances are revealed to firmly deposit on the micro-structured surfaces. More phosphate growth is seen for the higher laser energy. Discussions suggest that the additional elements deposition could be attributed to the chemical reaction of plasma related ions in the suspension and their subsequent crystallisation on the fresh surfaces of Ti plate due to the femtosecond laser ablation.

Influence of local environment on the intensity of the localized surface plasmon polariton of Ag nanoparticles

A combined Ag nanoparticle with an insulating or conductive layer structure has been designed tor molecular detection using surface enhanced Raman scattering microscopy. Optical absorption studies revealed localized surface plasmon resonance, which shows regular red shift with increasing environmental dielectric constant. With the combined structure of surface enhanced Raman scattering substrates and rhodamine 6C as a test molecule, the results in this paper show that the absorption has a linear relationship with the local electromagnetic field for insulating substrates, and the electrical property of the substrate has a non-negligible effect on the intensity of the local electromagnetic field and hence the Raman enhancement.