Thermally tunable random laser in dye-doped liquid crystals

A thermally tunable random laser in dye-doped liquid crystals (DDLCs) is reported. The gain medium of PM597 dye-doped E7 nematic LC is injected into a glass cell. The experimental results show that the random lasing is still obtained when the cell temperature becomes higher, even above the nematic–isotropic transition, and that its polarization changes at the same time. Temperature has little effect on the full width at half maxiumum of the random lasing. The center wavelength of the random lasing shifts from 575.69?nm to 593.43?nm when the temperature increases from 25.5°C to 148°C. Meanwhile, a random laser based on a solution of laser dye is first reported in this article. The reasons are possibly that nanoparticles consisting of dye molecules provide a new scattering mechanism in both solution and isotropic phase.     

Small angle neutron scattering and photoluminescence property of wet chemistry process synthesised ZnO nanoparticles

We report the synthesis of zinc oxide (ZnO) nanoparticles from aqueous solution at 25°C and subsequent heating of the solution at 115°C by the suitable selection of the solution chemistry and the control of the alkaline conditions. The structure of the synthesised ZnO particles was studied by X-ray diffraction (XRD), confirming the formation of Wurtzite structure. The optical property of synthesised ZnO nanoparticles is investigated through room temperature photoluminescence (PL) measurement. The PL of ZnO nanoparticles shows a strong UV emission band at approximately 385 nm, a blue–green band at approximately 473 nm and a very weak green band at approximately 554 nm, although polydispersity of the sample shows no presence on the PL spectrum. Small angle neutron scattering is used to determine the size and the size distribution of ZnO nanoparticles. The SANS data analysis and model fitting predict the size as about 18–20 nm, which is closely matched with XRD and transmission electron microscopy results with Gaussian distribution.     

Structural and chemical changes of thermally treated bone apatite

The thermal behaviour of the animal by-product meat and bone meal (MBM) has been investigated in order to assess how it is affected structurally and chemically by incineration. Initially composed of intergrown collagen and hydroxyapatite (HAP), combustion of the organic component is complete by 650 °C, with most mass loss (50–55%) occurring by 500 °C. No original proteins were detected in samples heated at 400 °C or above. Combustion of collagen is accompanied by an increase in HAP mean crystallite size at temperatures greater than 400 °C, from 10 nm to a constant value of 120 nm at 800 °C or more. Newly formed crystalline phases appear beyond 400 °C, and include β-tricalcium phosphate, NaCaPO₄, halite (NaCl) and sylvite (KCl). Crystallite thickness as judged by small angle X-ray scattering (SAXS) increases from 2 nm (25–400 °C) to 8–9 nm very rapidly at 550 °C, and then gradually increases to approximately 10 nm. The original texture of HAP within a collagen matrix is progressively lost, producing a porous HAP dominated solid at 700 °C, and a very low porosity sintered HAP product at 900 °C.     

Effect of laser-radiation polarization on the nonlinear scattering of light in nanodiamond suspensions

The effect of laser radiation polarization on the nonlinear scattering of light in aqueous suspensions of detonation nanodiamonds (DNDs) in a regime of optical power limiting (OPL) has been studied. It is established that the nonlinear transmission coefficient of DND suspension in the OPL regime in a field of nanosecond laser pulses with a wavelength of 532 nm is independent of the polarization of incident radiation. The nonlinear scattering of light observed at an angle of 90° in the plane perpendicular to the plane of polarization of the incident radiation depends on the polarization angle in accordance with a trigonometric law. It is shown that the ratio of the signals of scattered radiation for the vertical and horizontal polarizations exhibits nonmonotonic dependence on the laser-beam power density. The results are explained by the Rayleigh-Mie scattering and a change in the size of scattering centers as a result of the effect of a laser upon the DND suspension.     

A study of growth and surface performance analysis of nanographites grown using microwave plasma jet chemical vapor deposition system

Nanographites were grown using a microwave plasma jet chemical vapor deposition (MPJCVD) system. The E-H tuner of the MPJCVD was controlled by a personal computer. Monitoring of plasma jet was done through an optical emission spectroscopy and a charge coupled detector camera. High frequency structure simulator software was used to calculate electrical fields around specimens at different positions of the E-H tuner of the MPJCVD. Nanographites, composed of sp² hybrid orbital, were grown at a microwave power of 800?W. The carbon bonds, both C–C and C=C bonds, of as-grown nanographites were measured to have characteristic peaks at 1309 and 1595?cm^?1 using Raman spectroscopy. The mean size of the nanostructured graphite was nearly 50?nm under scanning electron microscopy observation. The measurement of contact angle on such graphite films was made by laying drops of deionized (DI) water, 0.03 and 0.09?M sodium chloride (NaCl) and was found to be 153°, 147°, and 136°, respectively. An electro-wetting test was also performed on the graphite films by adding electrical voltage through the CA measurement. It was found that contact angles of electro-wetting test for graphite films become 110° and 37° for DI water and NaCl solution, respectively.     

Cloud-droplet-size distribution from lidar multiple-scattering measurements

A method for calculating droplet-size distribution in atmospheric clouds is presented, based on measurement of laser backscattering and multiple scattering from water clouds. The lidar uses a Nd:YAG laser that emits short pulses at a moderate repetition rate. The backscattering, which is composed mainly of single scattering, is measured with a detector pointing along the laser beam. The multiple scattering, which is mainly double scattering, is measured with a second detector, pointing at a specified angle to the laser beam. The domain of scattering angles that contribute to the doublescattering signal increases monotonically as the pulse penetrates the cloud. The water droplets within the probed volume are assumed to have a constant size distribution. Hence, from the double-scatteringmeasured signal as a function of penetration depth within the cloud, the double-scattering phase function of the scattering volume is derived. Inverting the phase function results in a cloud-droplet-size distribution in the form of a log-normal function.     

The effect of pressure on spontaneous Rayleigh–Brillouin scattering spectrum in nitrogen

In order to study the effect of gas pressure on spontaneous Rayleigh–Brillouin scattering spectrum and verify the validity of Tenti S6 model at pressures up to 8 atm, the spontaneous Rayleigh–Brillouin scattering experiment in nitrogen was performed for a wavelength of 532 nm at the constant room temperature of 296 K and a 90° scattering angle. By comparing the experimental spectrum with the theoretical spectrum, the normalized root mean square deviation was calculated and found less than 2.2%. It is verified that Tenti S6 model can be applied to the spontaneous Rayleigh–Brillion scattering of nitrogen under higher pressures. The results of the experimental data analysis demonstrate that pressure has more effect on Brillouin peak intensity and has negligible effect on Brillouin frequency shift, and pressure retrieval based on spontaneous Rayleigh–Brillouin scattering profile is a promising method for remote of pressure, such as harsh environment applications. Some factors that caused experiment deviations are also discussed.     

Laser material processing of nickel superalloy for improved erosion resistance

A nickel-based superalloy was laser surface treated, and its erosion behavior was evaluated. The laser power and scan speed were varied in different levels to impart variations in microstructure and mechanical properties. The microstructure of specimens exhibited fine equiaxed grains to columnar structure at different parameters. A high cooling rate improved the hardness of the laser-treated specimen up to 603?HV_0.3 compared to the base material hardness of 430?HV_0.3. The rate of erosion increased linearly from 30° to 60° impingement angle and decreased at 75° impingement angle. The accumulation of the erodent inside the crater and the consequent absorbtion of the incident kinetic energy might have caused this reduction. The laser surface treated specimens exhibited ～1.5 factor of improvement in high temperature erosion resistance. This was attributed to the minimized energy transfer from impinging particle to the substrate achieved through laser surface melting.     

Comparative Study of Light Scattering from Hepatoma Cells and Hepatocytes

Primary liver cancer is one of the highest mortality malignant tumors in the world. China is a high occurrence area of primary liver cancer. Diagnosis of liver cancer, especially early diagnosis, is essential for improving patients?? survival. Light scattering and measuring method is an emerging technology developed in recent decades, which has attracted a large number of biomedical researchers due to its advantages, such as fast, simple, high accuracy, good repeatability, and non-destructive. The hypothesis of this project is that there may be some different light scattering information between hepatoma cells and hepatocyte. Combined with the advantages of the dynamic light scattering method and the biological cytology, an experimental scheme to measure the light scattering information of cells was formulated. Hepatoma cells and hepatic cells were irradiated by a semiconductor laser (532?nm). And the Brookhaven BI-200SM wide-angle light scattering device and temperature control apparatus were adopted. The light scattering information of hepatoma cells and hepatic cells in vitro within the 15°C to 30°C temperature range was processed by a BI-9000AT digital autocorrelator. The following points were found: (a) the scattering intensities of human hepatic cells and hepatoma cells are nearly not affected by the temperature factor, and the former is always greater than the latter and (b) the relaxation time of hepatoma cells is longer than that of hepatic cells, and both the relaxation time are shortened with increasing temperature from 15°C to 25°C. It can be concluded that hepatoma cells could absorb more incident light than hepatic cells. The reason may be that there exists more protein and nucleic acid in cancerous cells than normal cells. Furthermore, based on the length relaxation time, a conclusion can be inferred that the Brownian movement of cancer cells is greater.     

IR transparency of the glass of ZnCl2-KBr-PbBr2 system

IR transparency and some properties of halide glass of composition 48ZnCl₂-48KBr-4PbBr₂ (mol%) have been investigated as the basic study on the development of IR glass fiber for CO₂ gas laser. The glass transition temperature Tg, crystallization temperature T_c, softning temperature T_s, and linear thermal expansion coefficient α of the glass were found to be 45–46°C, 100°C, 54°C, and 570×10^?7 / °C, respectively. The refractive index of the glass for He-Ne laser emission (632.8 nm) was about 1.63. The amount of impurity which decreases the transmissibility for CO₂ laser beam due to the absorption in the wavelength region 10–11 μm could be reduced by preparing the glass from a batch containing NH₄ Cl under reactive atmosphere of CCl₄ or CBr₄ in a glove box filled with He gas of dew point ?62～ ?45°C. The minimum value of absorption loss of the glass for CO₂ gas laser measured by laser calorimetry was about 20 dB/m.     

球形粒子对平面偏振光散射的数值计算与分析

论文在Mie理论基础上,给出了球形粒子对平面偏振光的散射强度和散射系数公式,利用连分式递推算法进行了编程计算,重点对1.06μm激光的模拟结果进行了分析.从得到的散射图像可以看出,散射强度角分布与散射粒子尺度有密切关系,随着粒子尺度的逐渐增大,散射光强主要集中到前、后向散射方向,集中的角度越来越窄,模拟结果明显出现了散射强度最弱的极值角,且该极值角随粒径的增大而增大,最后逼近90°方向.散射强度角分布与波长有关,当它们在同一数量级时达到最大值,与散射粒子折射率无关.该递推算法因为每一步计算都是独立的,与前后项的准确性没有关系,不存在不稳定、发散等情况,能够计算粒径参数范围从10-4开始,对上限不受任何限制.     

Random laser action from ceramic-doped polymer films

We report random lasing emission from polymer films doped with ceramic particles in a gain medium. The Al₂O₃ particles and Rh6G laser dye-doped PVP films were fabricated by a spin-coating technique and they were exposed to a pulsed laser at 526 nm, by which we collected intensive feedback random laser (IFRL) emission when the pump energy reached thresholds. The threshold depended on particle size, film thickness and particle contents in solution. A model with randomly distributed scatterers was established to confirm that the scattering properties could strongly effect the thresholds and lasing spatial distributions.     

Spectral and spatial dynamics of a multimode GaN-based blue laser diode

ABSTRACT

High-resolution spectral analysis of a multimode GaN-based blue laser diode was performed as a function of temperature and current both below and above the threshold levels. Maps of longitudinal modes evolution as a function of current and temperature were obtained from the highly resolved emission spectra of the laser diode. The evolution of emitted longitudinal modes with current and temperature exhibited redshifts at rates of 0.0059 nm/mA and 0.0149 nm/°C, respectively. Similarly, the laser gain profile was observed to shift towards longer wavelengths but with rates of 0.022 nm/mA and 0.0439 nm/°C. The longitudinal mode spacing of 0.0540 nm was experimentally evaluated and compared with its equivalent theoretically predicted value.     

A New High-Temperature Oscillating Cup Viscometer

A new oscillating cup viscometer for temperatures up to 2,300°C has been constructed. A vacuum furnace with a graphite heater is used for heating the sample. The temperatures of the furnace and sample are measured by both a thermocouple and a pyrometer. The temperature is controlled with a stability better than 1 K. The oscillation of the cup is measured with a reflected laser beam using a position sensitive detector. The measured values of angle and time are then fitted to an analytical oscillation function. From the parameters of this function, the viscosity values are calculated using the Roscoe formalism. Measurements were carried out on pure metals at temperatures up to 1,700°C because of limitations of the thermocouple. The obtained viscosity values showed good agreement with literature data.     

Directional-hemispherical reflectance for spectralon by integration of its bidirectional reflectance

The directional-hemispherical reflectance is obtained for Spectralon, the material chosen for onboard radiometric calibration of the multiangle imaging spectroradiometer, at laser wavelengths of 442, 632.8, and 859.9 nm. With p- and s-polarized incident light and for an angle of incidence of 45 degrees , the bidirectional reflectance distribution function was measured over a polar angle range of 1-85 degrees and a range of azimuthal angles of 0-180 degrees in 10 degrees increments. The resultant directional-hemispherical reflectance is found by integration to be 1.00 ? 0.01 at 442 nm, 0.953 ? 0.01 at 632.8 nm, and 0.956 ? 0.01 at 859.9 nm. The experimental methodology and the data analysis are presented together with a full discussion of the primary experimental errors.     

Optimization design and analysis of reflecting polarizing beam splitter based on metal–multilayer dielectric grating for 800 nm

A new reflecting polarizing beam splitter (RPBS), based on a metal–multilayer dielectric grating (MMDG), was designed using rigorous coupled wave analysis method and a genetic algorithm. The RPBS reflects the TE wave in the ?1st order and TM wave in the 0th order for 800?nm. The optimized RPBS has an extinction ratio of over 20 dB, from 765?nm to 823?nm, and a large angle, from 43.8° to 60°. At 800?nm, the extinction ratios of the 0th and ?1st orders reach a maximum of 41.0 dB and 53.2 dB, respectively. Furthermore, analysis suggests that the designed RPBS allows sufficient manufacture tolerance. These results show the potential of MMDGs in fabrication of a RPBS, which can be widely used in optical systems.     

工艺参数对EB-PVD制备YSZ涂层的影响

为探讨电子束物理气相沉积(EB-PVD)制备8 mol.%氧化钇稳定氧化锆(8YSZ)涂层过程中工艺参数对涂层致密性、表面粗糙度和晶粒择优取向生长的影响,利用扫描电镜、原子力显微镜和X射线衍射技术对涂层的上述性能进行了分析.分析结果表明,随沉积速率由750 nm/min下降至20 nm/min,YSZ涂层的晶粒逐渐聚合长大,晶粒之间的孔隙减少,涂层的气体扩散系数相应地由2.41×10-4cm4/(N·s)下降至6.56×10-5cm4/(N·s).YSZ涂层的表面粗糙度随靶基距的提高逐渐降低,涂层的晶体学取向随蒸汽粒子入射角的改变而改变,入射角为30°时(111)晶面具有平行于涂层表面排列的趋势,入射角为45°时(311)和(420)晶面具有平行于表面排列的趋势,而入射角为60°时(220)和(331)晶面具有平行于表面排列的趋势.     

Analysis of a InGaAs/InP single photon detector at 1550 nm

A new type of single-photon detector is introduced and its related properties characterized. The single-photon detector operating in the Geiger mode uses a new type of cooling system to moderate temperature, which can make the temperature drop to ?65?°C. Besides, the single-photon detector adopts a hold-off time modulation feedback control circuit to decrease the afterpulsing effects and the gate pulse is coupled to the avalanche diode through capacitance. In addition, a suitable delay and comparator with latch function circuit are used to detect avalanche signals. Experimental conditions are that the clock frequency is 10 MHz, refrigeration temperature is ?65?°C, and the width of control pulse is 5 ns. The experimental results indicate that quantum efficiency is about 20.42% and the dark count rate is about 5 × 10^?6 ns^?1 with signal-to-noise ratio 27 dB at the optimum operation point of this detector. The designed single-photon detector achieves a tradeoff between lower dark count rates and high quantum efficiency.     

Wetting behaviour of laser textured Ti3SiC2 surface with micro-grooved structures

In the present paper, micro-grooved Ti₃SiC₂ surfaces with different roughness were fabricated by pulsed laser processing. The surface topography and chemical composition of smooth and micro-grooved surfaces were characterised. The wetting behaviours of smooth and micro-grooved Ti₃SiC₂ surfaces such as static contact angle, anisotropic wettability and contact angle evolution versus time were investigated. The experimental results show that micro-grooved structures can be efficiently fabricated on Ti₃SiC₂ surface by laser processing. The contact angle of micro-grooved surface was increased by 64.2° compared with that of smooth surface. The difference values of contact angles between perpendicular and parallel direction were <?10°. The wetting state of droplet on textured surface was close to Cassie–Baxter model.     

Synthesis of TiO2 nanotube films via pulsed laser deposition followed by a hydrothermal treatment

Titanium dioxide nanotube (TNT) films were prepared by pulsed laser deposition (PLD) of P25 and P90 TiO₂ nanoparticles onto stainless steel foils followed by a hydrothermal treatment (HT). Heating the PLD films in a TNT precursor solution at 150°C resulted in a well-adhered dense mat of TNTs that were ～10?nm in diameter with a pore size of ～4?nm. The TiO₂ nanotube films were characterised by SEM, TEM, XRD and Raman spectroscopy.