在a-平面蓝宝石衬底上分子束外延生长的ZnO和ZnMgO材料结构和光学性质(英文)

氧化锌材料是新一代宽禁带光电子半导体材料,我们通过等离子体分子束外延设备,在a plane的蓝宝石衬底生长了高质量的氧化锌外延材料。在生长过程中用反射高能电子束衍射仪(RHEED),在位地研究了生长时材料薄膜的表面形貌。通过调节ZnMgO材料镁的组份,生长了禁带宽度可调的宽禁带材料。用紫外-可见透射光谱研究了ZnO,Zn0.89Mg0.11O和Zn0.80Mg0.20O薄膜材料的透射和吸收光谱性质,观察到Zn0.89Mg0.11O,Zn0.80Mg0.20O材料的吸收边的蓝移现象等。以上说明了我们用分子束外延生长 收稿日期:2003 07 22·09·　　第1期StructuralandOpticalCharacterizationofZnOandZnMgOFilmsona-planesapphiresbyMolecularBeamEpitaxy2004年设备成功的生长了高质量的氧化锌和组份渐变的ZnMgO薄膜材料。     

基于可调谐二极管激光吸收光谱波长调制技术在线测量燃烧场温度

 介绍了可调谐二极管激光吸收光谱（TDLAS）波长调制技术的测温原理。通过选择水在1 397.75 nm和1 397.87 nm处两条邻近的吸收线,运用多功能数据采集卡对二极管激光器进行控制和信号采集,实现了TDLAS波长调制技术对标定燃烧炉甲烷/空气预混火焰温度的实时在线测量,测量重复频率为250 Hz。分析了温度测量数据抖动的原因,结果表明燃烧过程中火焰本身温度的抖动是测量结果波动的主要原因,测量系统的A类标准不确定度小于53 K。     

A diode laser system for spectroscopy of the ultranarrow transition in ytterbium atoms

A narrow-line diode laser system has been developed for high-resolution spectroscopy of the magnetic quadrupole transition in ytterbium (Yb) atoms at 507 nm. The system consists of an extended-cavity laser diode at 1014 nm, a tapered amplifier and a periodically poled lithium niobate nonlinear crystal which converts the wavelength from 1014 nm to 507 nm. We have stabilized the laser frequency and reduced the linewidth below 1 kHz by tightly locking the laser to a high-finesse optical cavity. By using the developed laser system, we have successfully observed the ultranarrow transition in Yb atoms. Furthermore, our simple and compact laser system could be a high performance and portable frequency reference using iodine spectra whose linewidth becomes less than 50 kHz around 507 nm. We have also demonstrated spectroscopy of iodine molecules. PACS 32.30.-r; 07.60.-j     

Ultra fast melting process in femtosecond laser crystallization of thin a-Si layer

In this paper, we investigated the mechanism of crystallization induced by femtosecond laser irradiation for an amorphous Si (a-Si) thin layer on a crystalline Si (c-Si) substrate. The fundamental, SHG, THG wavelength of a Ti:Sapphire laser was used for the crystallization process. To investigate the processed areas we performed Laser Scanning Microscopy (LSM), Transmission Electron Microscopy (TEM) and Imaging Pump-Probe measurements. Except for 267 nm femtosecond laser irradiation, the crystallization occurred well. The threshold fluences for the crystallization using 800 nm and 400 nm femtosecond laser irradiations were 100 mJ/cm² and 30 mJ/cm², respectively. TEM observation revealed that the crystallization occurred by epitaxial growth from the boundary surface between the a-Si layer and c-Si substrate. The melting depths estimated by Imaging Pump-Probe measurements became shallower when the shorter wavelength was used.     

Analysis of a separate 1319 and 1338 nm Nd:YAG laser with a blazing grating

We develop a separate 1319 and 1338 nm Nd:YAG laser system with a blazing grating (600 lines/mm). The resonator of this system has a Littrow grating configuration and a highly reflective mirror, in which the zero-order diffraction of the grating acts as the laser output. By virtue of the wavelength-dependent reflectivity of the grating, a single-wavelength laser at 1319 nm or 1338 nm can be realized. In view of the laser rate equations and using the distribution of the blazing grating, we analyze the oscillation conditions providing single-wavelength laser operation in the system.     

利用钟跃迁谱线测量超稳光学参考腔的零温漂点

在87Sr光晶格钟实验系统中,通过将自由运转的698 nm激光频率锁定在由超低膨胀系数的玻璃材料构成的超稳光学参考腔上,从而获得短期频率稳定性较好的超稳窄线宽激光.超稳光学参考腔的腔长稳定性决定了最终激光频率的稳定度.为了降低腔长对温度的敏感性,使激光频率具有更好的稳定度和更小的频率漂移,利用锶原子光晶格钟的钟跃迁谱线,测量了698 nm超稳窄线宽激光系统中超稳光学参考腔的零温漂点.通过对钟跃迁谱线中心频率随温度的变化曲线进行二阶多项式拟合,得到698 nm超稳窄线宽激光系统的零温漂点为30.63℃.利用锶原子光晶格钟的闭环锁定,测得零温漂点处698 nm超稳窄线宽激光系统的线性频率漂移率为0.15 Hz/s,频率不稳定度为1.6×10^–15@3.744 s.     

绝缘衬底上高密度均匀纳米硅量子点的形成与表面形貌

利用等离子体增强化学气相淀积技术，在绝缘氮化硅(SiNx)衬底上制备超薄非晶硅(aSi：H)薄膜，通过超短脉冲激光辐照与准静态常规热退火技术处理，制备出高密度、均匀纳米硅(ncSi)量子点.使用原子力显微镜对处理前后样品的表面形貌进行了研究，发现激光辐照能量密度增加的同时，所形成的ncSi尺寸也随之增加.在合适的能量密度范围内，可以得到面密度大于10.11cm^2、尺寸分布标准偏差小于20％的10 nm ncSi量子点薄膜，表明所制备的ncSi量子点具有较好的均匀性及较高的面密度.同时，对ncS i量子点 关键词： 纳米硅 激光诱导 尺寸分布     

Development of an optical parametric generator with pulsed dye amplification for high-resolution laser spectroscopy

An injection-seeded optical parametric generator (OPG), coupled with three pulsed dye amplification (PDA) stages, was shown to produce tunable, narrow linewidth laser radiation. The OPG was composed of a pair of beta barium borate (β-BBO) crystals and pumped by the third harmonic (355 nm) output of a seeded Nd:YAG laser. The OPG was injection-seeded at the idler wavelength (824 nm) using an external cavity diode laser (ECDL) with a mode-hop-free tuning range of 20 GHz. Using the PDA stages, the OPG output signal (624 nm) was amplified to 19 mJ/pulse, while maintaining a spectral linewidth of approximately 160 MHz at full-width-half-maximum (FWHM) which was within a factor of 2 of the Fourier limit. A system of lenses and apertures was used to minimize amplified spontaneous emission (ASE) in the PDA stages. Using the OPG/PDA system, two-photon laser-induced fluorescence measurements of atomic oxygen were performed by sum-frequency-mixing the 624-nm beam with the third harmonic output of the seeded Nd:YAG laser to generate approximately 1 mJ/pulse of ultraviolet radiation near 226 nm. Voigt line shapes were found to be in good agreement with oxygen atom spectra in atmospheric-pressure, laminar, counter-flow flames; the magnitude of Doppler and collisional broadening was approximately the same. The measured O-atom concentration profile was found to compare well with that calculated using an opposed-flow flame code.     

243 nm稳频窄线宽半导体激光器

243 nm是氢原子1S-2S能级跃迁光谱波长. 本文利用Pound-Drever-Hall稳频技术将972 nm光栅反馈外腔半导体激光稳定在一个高精细度低膨胀系数的超稳法布里-珀罗腔上, 通过锥形放大器放大和腔内两次共振增强倍频得到243 nm激光, 最终实现用于探测氢原子1S-2S双光子跃迁的243 nm窄线宽激光.     

Photo-conversion and evolution of one-dimensional Cu nanoparticles under femtosecond laser irradiation

Metal nanowires with electric conductive properties can be useful for optical polarization control medium and electro-conductive nanomaterial. We report on metallic Cu nanowires with a length of 1.0 μm and a diameter of 85 nm which were successfully photo-converted from commercial scale-like Cu particles, dispersed in a methanol solution, by using femtosecond laser irradiation. The growth mechanism of Cu nanowires under laser irradiation was suggested to be a nucleation growth process.     

Silicon nanowires synthesized by vapor–liquid–solid growth on excimer laser annealed thin gold film

The fabrication of Si nanowires has been demonstrated using excimer laser annealed thin gold film as the catalyst and vapor–liquid–solid (VLS) growth. Au nanoparticles with mean diameters of 12, 13 and 15 nm were formed by excimer laser annealing (ELA) of Au film with thickness of 2.5, 5 and 10 nm, respectively. The results show that the silicon nanowires (SiNWs) with desired diameter can be obtained by controlling the Au film thickness and laser power density.     

Remote imaging laser-induced breakdown spectroscopy and remote cultural heritage ablative cleaning

We report, for what we believe to be the first time, on remote imaging laser-induced breakdown spectroscopy (LIBS). Measurements have been performed by using a tripled Nd:YAG laser working at 355 nm with 170 mJ pulse energy, with an expanded beam that is focused onto a target at 60 m distance. The LIBS signal is detected by using an on-axis Newtonian telescope and an optical multichannel analyzer. The imaging is performed by scanning the laser beam on the target. The same setup is also used in demonstrations of remote laser ablation for cleaning of contaminated objects with applications toward cultural heritage.     

Excimer laser patterned dielectric masks for the fabrication of diffractive optical elements by laser ablation

Masks for laser processing are generated by laser ablation patterning of dielectric layer systems. The application of these masks for the rapid fabrication of diffractive optical elements (DOEs) is presented. The diffractive optical elements are designed as phase-only elements, assuming an illumination with a plane wave. A continuous phase function is calculated using an iterative Fourier transform algorithm (IFTA). This continuous phase function is reduced to two or four levels by an iterative Fourier quantisation algorithm (IFQA) that is able to include focal power. The fabrication of the DOE is performed in a two-step process. First, a binary amplitude mask (or a set of masks for multi-level DOEs) is made by structured ablation of a highly reflective dielectric coating (HR 248 nm) from a fused silica substrate. This is accomplished by using an ArF excimer laser emitting at 193 nm, a wavelength that is sufficiently absorbed in the HfO₂/SiO₂-dielectric layer system, leading to precisely ablated mask structures. In the second step, this mask is used in a 4:1 projection configuration to generate a surface profile in a polymer substrate by ablation at 248 nm. The depth modulation can be defined by adjusting laser fluence and pulse number. Examples of DOEs ablated in polycarbonate are shown and their performance is characterised.     

基于拉曼光谱散射的新型分布式光纤温度传感器及应用

介绍了分布式光纤拉曼温度传感器(DTS)的基本原理、发展趋势和工程应用研究状况,研究了分布式光纤拉曼温度传感器的关键技术,全面提升了DTS的性能。将拉曼放大技术应用于DTS系统,用拉曼增益部分抵偿光纤的传输损耗,使系统的传感长度达到50 km;对脉冲激光器进行211位循环编码,在接收时采用相关运算解调,显著提高系统的信噪比,使测温不确定度达到1 ℃;采用双波长自校正技术提高了系统的空间分辨率,达到2 m;在DTS系统中嵌入光开关,使测温通道成倍扩展,有效延伸了传感光纤的总长度,组成光纤传感网络。     

Ultra-high-precision mid-IR spectrometer II: system description and spectroscopic performance

The development and spectroscopic performance evaluation of an ultra-sensitive, mid-IR spectrometer is reported. The laser system is based upon difference-frequency generation (DFG) at ～3.5 μm by mixing a DFB diode laser at 1562 nm and a DFB fiber laser at 1083 nm using a periodically poled LiNbO₃ crystal. DFG radiation was coupled to a 100?m optical path length astigmatic Herriott cell. Sensitive and selective spectroscopic detection of formaldehyde was performed with second-harmonic detection using Peltier-cooled HgCdTe detectors. By applying computer lock-ins, dual-beam optical noise subtraction, focus matching, thermal stabilization, active wavelength control, and advanced signal processing a sensitivity corresponding to an absorbance ～1.6×10^-7 is achieved for 260 s of averaging.     

Anti-Stokes Raman laser investigations on atomic Tl and Sn

Anti-Stokes Raman laser experiments using metastable atomic Tl and Sn have been performed. The required metastable population inversion is generated by photodissociation of TlI and SnBr₂ with KrF laser radiation. The Tl(Sn) system permits frequency up-conversion by 7793 cm^–1 (17,163 cm^–1). By optimization of system parameters, uv output energies up to 2.5 mJ (377 nm) and conversion efficiencies of more than 25% have been achieved for Tl. Further improvements and principal limitations will be discussed.     

Performance study of a soft X-ray harmonic generation FEL seeded with an EUV laser pulse

The performance of a free electron laser (FEL) using a low-power extreme ultraviolet (EUV) pulse as an input seed is investigated. The parameters are appropriate for 30 nm seeds produced from high-power Ti:Sapphire pulses using high harmonic generation schemes. It is found that, for reasonable beam parameters, robust FEL performance can be obtained. Both time-independent and time-dependent simulations are performed for varying system parameters using the GENESIS simulation code. A comparison is made with a two-stage harmonic FEL that is seeded by a high-power Ti:Sapphire pulse.     

Size dependent optical characterization of semiconductor particle: CdS embedded in polymer matrix

We report the optical investigation and analysis of both nano-sized and micrometer size Cadmium Sulphide particles which is embedded in a transparent polyvinyl alcohol (PVOH) dielectric host material. A designed and fabricated laser based light scattering system using a He-Ne laser of wavelength 632.8nm was used for the measurement and study of the scattering properties of the particles as a function of the scattering angle at this wavelength. An attempt was made to experimentally determine the most significant elements of the Mueller scattering matrix using combinations of randomly and linearly polarized incident laser beam and subsequent analyzers in corresponding orientations. The analysis of the experimental data was done by the method of comparison with theoretically generated data. Novel computational technique, involving single scattering for spherical particles using Mie-theory, was developed and applied. The theoretical data was found to be in good agreement with the experimental data within an acceptable margin of error. The results have proved that the combination of the experimental setup and associated computational method is a highly efficient and reliable in-situ system for monitoring size growth of semiconductor particles in the laboratory.     

周期极化KTiOPO4晶体和频单块非平面环形腔激光产生连续单频589nm黄光

单次通过周期极化KTiOPO₄晶体和频单块非平面环形腔1064 nm与1319 nm激光产生连续单频589 nm黄光. 通过琼斯矩阵模拟计算对单块非平面Nd:YAG晶体参数进行了优化设计, 实验获得1080 mW和580 mW的连续单频1064 nm和1319 nm激光输出. 两束激光单次通过周期极化KTiOPO₄晶体和频产生14.8 mW, M²=1.14的589 nm黄光, 相应的和频效率为0.9%. 研究了周期极化KTiOPO₄温度对和频效率的影响, 得到其温度接收带宽为1.5℃. 通过改变1064 nm Nd:YAG晶体的温度可实现589 nm黄光波长精确对应钠原子D_2a吸收谱线, 调谐精度达到0.164 pm.     

Determination of the ratio of soot refractive index function E(m) at the two wavelengths 532 and 1064 nm by laser induced incandescence

A new method is proposed to measure the ratio of the refractive index function of soot particles E(m) at the two fixed wavelengths: 532 and 1064 nm. Using a non-intrusive, in-situ laser based technique, the ratio E(m,1064 nm)/E(m,532 nm) can be determined by comparing laser induced incandescence (LII) intensities at 532 and 1064 nm excitation wavelengths. The method consists of selecting laser energies that insure the equality of the LII signals in the low fluence regime under given conditions. Such equality is consistent with the fact that the soot particle will have reached the same temperature independently of the laser wavelength, i.e. the soot particle has absorbed the same energy. As the absorbed energy is proportional to the laser irradiance times E(m), the measurement of the laser energies required to insure perfect concordance of the LII intensities (spatially and temporally) serves to deduce the ratio E(m,1064 nm)/E(m,532 nm). The method is demonstrated in an acetylene/air flame, validated against extinction measurements performed by cavity ring-down spectroscopy (CRDS) by using laser radiations at 532 nm and 1064 nm and finally applied to different flame conditions. PACS 78.20.Ci; 78.90.+t; 81.05.Uw; 42.62.-b