Yb:YAG absorption at ambient and cryogenic temperatures

We have performed absorption measurements and generated absorption cross sections as a function of wavelength for the laser material YAG doped with ytterbium at 300, 175, and 75 K. This data was generated to enable a direct comparison of the absorption intensity and linewidths at room and cryogenic temperatures, and in particular near the temperature of liquid nitrogen at 77 K. The data have been used to compute universal absorption contour plots that display absorption as a function of the incident light center wavelength and optical thickness (doping density times penetration depth) for a number of bandwidths, and assuming that the spectrum of the incident light can be described as a Gaussian. Curves are presented for both 300 and 75 K, and may be used to optimize the absorption and laser efficiency.     

Passive optical limiting of picosecond-nanosecond laser pulsesusing highly nonlinear organic liquid cored fiber array

We present a detailed account of theoretical and experimental studies of nonlinear molecular photonic processes accompanying the propagation of short intense laser pulses through an organic liquid cored fiber array. The theory takes into account two-photon absorption, excited state absorption, and dynamical evolution of the molecular energy level populations and the laser intensity. The coupled dynamical equations for the molecular energy-level populations and laser intensity are solved numerically using experimentally observed molecular and optical parameters. Experimentally obtained optical limiting results are analyzed along with nonlinear absorption and pump-probe studies of other nonlinear optical processes occurring in the fiber core. It is found that in the nanosecond time regime, besides excited state and two-photon absorption, thermal and density effects also contribute significantly to the optical limiting performance of the constituent fiber     

Switching characteristics of vacuum gap switch employing UV‐laser triggering

The switching time and arc‐ignition probability of a sustained main discharge in a laser trigger vacuum gap were measured. The third harmonic beam of an Nd:YAG pulse laser (wavelength 355 nm, energy 5 mJ/pulse, power density 4 × 10⁷ W/cm²) was used to trigger the gap. The main electrodes 85 mm in diameter were made of oxygen‐free copper. The gap length was 1.6 mm and the experimental chamber was evacuated to about 1.3 × 10⁴ Pa by a turbomolecular pump. The UV beam from the laser was focused at normal incidence onto the grounded cathode. The switching time decreased and the arc‐ignition probability increased with increasing applied voltage. The switching time was 326 ns at 15 kV with a circuit inductance of 107 μH. Its jitter was 24.8 ns. The advantageous results obtained with the UV beam are compared to the previously reported data on triggered vacuum gaps. © 2000 Scripta Technica, Electr Eng Jpn, 132(3): 8–13, 2000     

Qualitative identification of nitrate nitrogen in compound fertilizers by infrared spectroscopy

ABSTRACT

In this study, NPK compound fertilizers containing nitrate nitrogen were tested by Fourier transform infrared spectroscopy (FTIR), and the relative contents of nitrate nitrogen and qualitative comparison were qualitatively identified. The raw materials of compound fertilizers: agricultural ammonium nitrate (AN), potassium nitrate (KNO₃) and ammonium phosphate (NH₄)₂HPO₄ were analyzed by infrared spectroscopy respectively. The results showed that the absorption peaks of nitrate (NO₃^?1) in solid agricultural fertilizers were 1384 cm^?1, 825 cm^?1. Furthermore, the NPK compound fertilizer with 4%, 5.5%, 6% and 9.5% nitrate nitrogen content were respectively tested by infrared spectroscopy. The results showed that with the increase of nitrate nitrogen content in the compound fertilizers, the relative intensity of the infrared absorption peaks of nitrate increased as well. Moreover, the relative intensity of the absorption peaks at 1384 cm^?1 and 825 cm^?1 are proportional to the content of nitrate in the nitro-compound fertilizer-containing ammonium nitrogen and nitrate nitrogen.     

Measurement of space-charge field in doped LiNbO3 single crystals

In order to measure the space-charge field in MgO-doped LiNbO₃, we examined the variation of second-harmonic intensity by an external DC electric field and a single beam pump. Intensities of illuminated beam were 3.9 and 7.8 W/cm². An external DC field was applied in the direction of spontaneous polarization (i.e. c-axis). Generated second-harmonic intensity as a function of DC electric field represented by the function of (cosine)². Space-charge field formed as a function of the exposure time of a laser beam had a exponential function. In 4 mol% MgO-doped LiNbO₃ of 6.8 kV/cm at 3.9 W/cm², the saturated space-charge field had a minimum value and the relaxation time had a maximum value.     

脉冲激光清洗典型污秽瓷式绝缘子温度特性分析

脉冲激光清洗瓷式绝缘子表面污秽会产生强烈的热效应,分析清洗过程中的温度特性至关重要。文中以沾污的瓷式绝缘子为研究对象,通过仿真和实验相结合的方法,研究不同典型污秽、不同污秽含水量、不同激光能量密度及波长等工况下温度场的变化规律。结果表明:温度的高低与污秽含水量、激光能量密度成正比,与激光波长成反比,其中激光湿式清洗比干式清洗效率高;在保证绝缘子瓷材料的抗热稳定性的前提下,激光能量密度处于2.52～3.81 J/cm~2,扫描速度1 000 mm/s时,不会损伤绝缘子基底材料,可达到最佳清洗。     

Optical bistability in lead magnesium niobate ceramics: An integrated photonic flow-rate/pressure gauge based upon thermal focussing and convection

We have discovered an unusual form of optical bistability in hot-pressed ceramic PMN (PbMg_0.3Nb_0.5Ti_0.1O₃) in which the thermal focussing of laser light at very low power densities (<1 kW/cm²) oscillates between two metastable states. At low laser powers P the phenomenon is highly aperiodic but extremely reproducible; the oscillation events occur at times t_N empirically given by the equation t_N = A/(P-P_N ), where the threshold power P_N for the N-th switching event is found to be NP_o , with P _o = 45 mW [i.e., 3.6 W/cm²]. At higher laser power the switching events become periodic, ca. 8 Hz, and resemble the phenomenon reported by Vasnetsov in thin films of thermotropic liquids. One of the two metastable spatial light patterns is doughnut-shaped; the other resembles a Bessel function, with large intensity in the center. Therefore by setting a Si-diode detector in the center of the pattern, we can monitor the oscillation. The oscillation event times (or frequency) are strongly dependent upon convection from the sides of the PMN thermal lens. Therefore the device acts as an optical (“photonic”) sensor that is extremely acute to pressure and flow rate of the surrounding atmosphere. We have measured pressure changes of 10^?2 Torr and flow rate changes of 0.1 cu. ft/hr. (0.3 m/s) in air.     

Effect of discharge power density on the properties of Al and F co-doped ZnO thin films prepared at room temperature

ZnO transparent conducting thin films co-doped with aluminium and fluorine (AZO:F) were prepared on glass substrates by RF magnetron sputtering at room temperature. The effect of discharge power density on the microstructure, surface morphology, electrical and optical properties was investigated. From XRD analysis, it was revealed that the intensity of (002) favoured orientation of ZnO films increased with power density from 2.6 to 6.1?W/cm² and then turned to a randomly orientated structure as power density continuously increased to 7.8?W/cm². The film prepared at 6.1?W/cm² showed a better crystallization and microstructure with larger, pyramid-like grains that were approximately 180?nm long and 90?nm wide. As a result, the electrical resistivity of the AZO:F films had a minimum of 4.1?×?10^?4???cm. The improvement in the electrical resistivity of AZO:F films was due to the increase in carrier concentration from 8.8?×?10²⁰ to 1.38?×?10²¹?cm^?3 and the mobility from 5.8 to 11.8?cm² V^?1 s^?1. The increase in carrier concentration with power density was also found to affect the optical property of the films due to the Moss-Burstein shift.     

Mechanoluminescence of Ca2MgSi2O7: Eu2+, Dy3+ Phosphor by Impulsive Deformation

Di-calcium magnesium silicate phosphor doped with Eu²⁺ and Dy³⁺ was prepared using solid state reaction technique under a reducing atmosphere. Prepared sample suffered an impulsive deformation with an impact of a piston for mechanoluminescence (ML) investigations. A temporal characteristic of ML of the phosphor was observed, which expressed single sharp peak with a long decaying section. In order to investigate about the luminescence centre responsible for ML peak, ML spectrum of the same phosphor was also observed. ML spectrum recorded shown similarity in shape as well as peak wavelength with Photoluminescence (PL) spectrum that verifies the existence of single emission centre due to the transition of Eu²⁺ ions i.e. transitions from any of the sublevels of 4f⁶5d¹ configuration to ⁸S_7/2 level of the 4f⁷ configuration. Decay rates for different impact velocities were also calculated using curve fitting technique. Time of ML peak and rate of decay did not change largely with respect to increasing impact velocity of the load and peak ML intensity varied linearly. Increasing impact velocity causes more number of Eu²⁺ ions to get excited to the higher energy level, subsequently de-excitation of more Eu²⁺ ions occurs. This gives rise to increase in ML intensity.     

Theory of relativistic optical harmonic generation

We present a theoretical model of optical harmonic generation excited by laser beams sufficiently intense that relativistic effects are important. This model shows that, under relativistic conditions, third-harmonic generation can be excited with comparable efficiency by either linear or circularly polarized light. This result is to be contrasted with experience from traditional (nonrelativistic) nonlinear optics, where group-theoretical arguments show that third-harmonic emission cannot occur under circularly polarized excitation. These results are in good agreement with the observed polarization dependence of the third-harmonic emission reported recently in an experiment conducted under conditions such that relativistic effects are important. Our theoretical model also predicts that all even and odd harmonies of the fundamental laser frequency are emitted in the near-forward direction with an intensity that increases with that of the incident laser field     

Generalized optical gain analysis in nonparabolic semiconductor laser

A simple generalized theory is developed for optical gain of nonparabolic semiconductor lasers based on the three‐band model of Kane, by taking into account the wave‐vector () dependence of the optical matrix element. The gain in laser of nonparabolic semiconductors is demonstrated, by taking InAs, InSb, Hg_1−xCd_xTe and In_1−xGa_xAs_yP_1−y lattice matched to InP as examples, and it has been found that the peak of the gain spectra for a given carrier density is higher in the three‐band model of Kane than those with parabolic energy band approximations in all the cases. The difference between the peak of gain spectra for three‐band model and the parabolic band model is greater for laser of narrow band gap materials in comparisons with that of laser of wide band gap materials, thereby reveals the necessity for inclusion of the nonparabolicity in modeling lasers of small band gap materials. The well‐known results for wide band gap materials having parabolic energy bands has also been obtained from our generalized formulation under certain limiting condition. Copyright © 2013 John Wiley & Sons, Ltd.     

Low temperature growth of sol-gel SrBi2Ta2O9 thin films by low-pressure annealing

A new low-temperature processing method to prepare SrBi₂Ta₂O₉ thin films is proposed. These thin films were prepared on Pt/Ta/SiO₂/Si substrates by a sol-gel method, and their structural and electrical properties were investigated. Films were annealed before and after the top Pt electrode deposition. The first annealing was performed in a 760-Torr oxygen atmosphere at 600 °C for 30 min, and the second annealing was performed in a 5-Torr oxygen atmosphere at 600 °C for 30 min. The films were well crystallized and fine-grained after the second annealing. The electrical characteristics of the 200-nm-thick film obtained by this new process were as follows: remanent polarization, P_r = 8.5 μC/cm²; coercive field, E_c = 36 kV/cm; and leakage current density, I_L = 1 × 10⁻⁷ A/cm² (at 150 kV/cm). This process is very attractive for highly integrated ferroelectric nonvolatile memory applications. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(2): 27–33, 1997     

变压器油中溶解气体的红外吸收特性理论分析

气体的红外吸收特性是红外光学方法分析气体的依据。基于HITRAN2004数据库用逐线积分法对变压器油中溶解气体CH4、C2H6、C2H4、C2H2、CO、CO2及H2O的红外吸收特性进行分析,给出各气体在波段500~4 000 cm-1内的吸收系数、主要吸收谱带位置、最强吸收谱线的中心波数及其峰值吸收系数;以各气体特征频谱处的吸收谱线为研究对象,分析峰值吸收系数随压强、温度的变化规律。计算和分析结果是用傅里叶变换红外光谱、光声光谱等红外光学方法对变压器油中溶解气体进行定性定量分析的重要依据。     

The electronic structures for the optical absorption of Hf-O-N thin films

The local structures of Hf-O-N thin films were analyzed using an extended X-ray absorption fine structure (EXAFS) study on Hf L _III-edge and first-principles calculations. Depending on their composition and atomic configurations, Hf₄O₈ (CN: 7.0), Hf₄O₅N₂ (CN: 6.25) and Hf₄O₂N₄(CN: 5.5) were suggested as the local structures of Hf-O-N thin films. The optical band gaps of Hf-O-N thin films were compared with the calculated band gap. And to investigate the optical absorption, the effects of film compositions on the valence bands of Hf-O-N thin films were analyzed by comparing the experimental valence band with the valence band.     

Development of a laser radar using LDS dye and sum frequency generation for NO2 measurement

A laser radar for measuring vertical concentration profiles of atmospheric NO₂ was developed. The laser transmitter uses an LDS765 dye laser pumped by a Nd:YAG laser. The dye laser output is converted to wavelengths 446.8 and 448.1 nm, which are used for NO₂ measurement, by sum frequency generation (SFG) using a pair of KD^*P crystals. The dependence of the LDS765 dye laser output on wavelength and dye concentration was investigated, and the performance of the laser transmitter was evaluated. Compared to the Coumarin 445 dye laser conventionally used for NO₂ measurement, this laser transmitter represents a significant improvement in output stability, as well as in maximum output energy and overall conversion efficiency. Using the newly developed laser radar, NO₂ concentrations of 20 to 40 ppb were measured for vertical range 500 to 1000 m, which were in rough agreement with values monitored on the ground. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(2): 26–33, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10231     

多谱线TDLAS测温中谱线选择的实验研究

采用可调谐半导体激光吸收光谱技术,利用两条谱线可以测量激光路径上的平均温度。在利用多条谱线测量激光路径的平均温度时,测量的精确度主要受制于测量信号的离散程度以及谱线低能级能量的分散程度。利用中心波长为1392.5 nm(7181.32 cm~(-1))的激光器快速扫描4条H_2O的波数为7182.950、7182.209、7181.156、7179.752 cm~(-1)的吸收谱线,研究了不同的谱线组合方式对激光路径平均温度测量精密度的影响。实验结果表明,进行谱线选取时,通过依次去掉一条谱线并计算其余谱线测量标准偏差的结果,能够快速反映出被去掉谱线对温度测量精确度的权重。通过谱线选择,测量得到的路径上平均温度的标准偏差小于20 K。     

运动原子的高精度测量

本文研究级联三能级原子通过驻波光腔时的高精度测量.驻波激光场与级联原子的上跃迁耦合,其拉比频率依赖于原子通过驻波场的位置.用一束弱探测激光与原子下跃迁耦合.通过探测原子激发态的分布概率,可以确定原子被局限在一个波长范围的4个不同位置,测量精度达到百分之一个光波波长.     

Optical parametric amplification of femtosecond ultraviolet laser pulses

Broad-band amplification of femtosecond laser pulses using the scheme of noncollinear optical chirped pulse parametric amplification is modeled. The effect of two-photon absorption at the pump wavelength was also taken into account. The signal pulses range from 220 to 410 nm with pump pulses at 267, 248, and 213 nm. The best four crystals chosen among 12 possible ones are BBO, KDP, CLBO, and LB4. In an experiment, 30-fs laser pulses at 400 nm were amplified in a BBO crystal pumped by 267 nm pulses, exhibiting a single pass gain of 3550. The gain was found spectrally flat within the available 17-nm bandwidth of the signal pulse.     

Optical guiding of intense laser pulses by fast Z-pinch discharge

We have proposed the optical guiding of intense laser pulses by fast Z-pinch for channel-guided laser wakefield acceleration (LWFA). The method has been developed based on capillary discharge-pumped X-ray laser technique. A discharge through preionized helium gas driven by a current of 4.8 kA with a rise time of 15 ns proved able to produce a uniform guiding channel with good reproducibility, less than the time jitter of 1.8 ns. The observed guiding channel formation process was corroborated by 1D-MHD simulation. With this new guiding method, an intense Ti-sapphire laser pulse (λ = 790 nm, 2.2 TW, 90 fs, 1 × 10¹⁷ W/cm²) was transported through the channel over a distance of 2 cm, corresponding to 12.5 times the Rayleigh length. © 2001 Scripta Technica, Electr Eng Jpn, 136(3): 19–27, 2001     

Simulation of Absorption Spectra of Metal Nanoparticles Embedded in Organic Media

Metal nanoparticles, silver and gold, of different sizes and shapes are actively being researched in a variety of different fields such as solar cells. The unique plasmonic properties of these particles, especially in the visible and NIR-region ranging from 400-1200 nm, are the basis for most of these applications. The absorption spectra are calculated using the discrete dipole approximation (DDA) in the wavelength region of 300 to 1200 nm. The modeled samples for calculating are planar array nanoparticles, basically two particles and more than two particles. The influences of the nanoparticle size, interparticle distance and polarization direction of excited light on the absorption spectra are investigated. Moreover, the optical absorption can be tuned by adjusting sizes and shape of nanoparticles to obtain the enhanced absorption. The influence of the surrounding medium is also presented.