A novel CO2 gas analyzer based on IR absorption

Carbon dioxide (CO₂) gas analyzer can be widely used in many fields. A novel CO₂ gas analyzer based on infrared ray (IR) absorption is presented sufficiently in this paper. Applying Lambert–Beer Law, a novel space-double-beam optical structure is established successfully. The optical structure includes an IR source, a gas cell, a bandpass filter with a transmission wavelength at 4.26 μm, another bandpass filter with a transmission wavelength at 3.9 μm, and two IR detectors. Based on Redial Basic Function (RBF) artificial neural network, the measuring model of IR CO₂ analyzer is established with a high accuracy. A dynamic compensation filter is effectively designed to improve the dynamic characteristic of the IR CO₂ analyzer without gas pump. The IR CO₂ analyzer possesses the advantages of high accuracy and mechanical reliability with small volume, lightweight, and low-power consumption. Therefore, it can be used in such relevant fields as environmental protection, processing control, chemical analysis, medical diagnosis, and space environmental and control systems.     

Raman Spectra Study on LiTa0.9Nb0.1O3 Single Crystal

In this letter, Raman spectra of LiTa_0.9Nb_0.1O₃ single crystal in both of its ferroelectric phase and paraelectric phase are presented for the first time. Comparing with LiTaO₃ crystal, we find that the distribution and Raman shifts of normal vibrational mades are similar, but the line-shape and relative intensities of these modes have changed.     

Ultraviolet laser-induced voltages in LaSrAlO4 single crystal

Laser-induced ultrafast photovoltaic effect is observed in LaSrAlO4 single crystal at ambient temperature without any applied bias. An open-circuit photovoltage is obtained when the wafer is irradiated by a 248-nm-KrF laser pulse of 20 ns duration. The response time and full width at half maximum of the photovoltage pulse are 6 ns and 19 ns, respectively, indicating that LaSrAlO4 single crystal has potential application in ultraviolet detector.     

Growth and optical properties of Mg, Fe Co-doped LiTaO3 crystal

Mg, Fe double-doped LiTaO₃ and LiNbO₃ crystals have been grown by Czochralski method. The optical properties were measured by two-beam coupling experiments and transmitted facula distortion method. The results showed that the photorefractive response speed of Mg:Fe:LiTaO₃ was about three times faster than that of Fe:LiTaO₃, whereas the photo-damage resistance was two orders of magnitude higher than that of Fe:LiTaO₃. In this paper, site occupation mechanism of impurities was also discussed to explain the high photo-damage resistance and fast response speed in Mg:Fe:LiTaO₃ crystal.     

Second-Harmonic Generation in Domain-Inverted Grating Induced by Focused Ion Beam

The fabrication of a periodic domain inversion in LiTaO₃ and LiNbO₃ using direct ion-beam writing is presented. The polarization of these materials can be reversed at room temperature by irradiating Si²⁺ ions into +c faces. A first-order periodic domain inversion with a 50% duty cycle, a depth of 300μ, and an interaction length of 1 mm was realized in LiTaO₃. Using this structure, 300μW of blue light was generated for a conversion efficiency of 0.25%/W.     

DFT - based study of electronic structures and mechanical properties of LiTaO3: ferroelectric and paraelectric phases

Abstract

By applying ab initio calculation within density functional theory (DFT), we study the structure parameters, electronic band structure, elastic coefficients, polycrystalline elastic properties, anisotropy factors and Debye temperature of ferroelectric and paraelectric phases of LiTaO₃ within the generalised gradient approximation at ambient pressure. The atomic structure in both phases is fully relaxed and the lattice constant, angle and atomic positions are well consistent with experimental values. The computed single-crystal elastic coefficients indicate that mechanical stability of LiTaO₃ in both phases is confirmed using the generalised Born criteria. The shear, bulk and Young’s modulus, Poisson’s ratio, and Vickers hardness were computed according to theoretical elastic constants by Voight–Reuss–Hill method. Several anisotropy factors and indexes are computed to illustrate mechanical anisotropy. Both phases are shown to be weakly anisotropic. The Debye temperature is estimated using the longitude and transverse elastic wave velocity of the ideal polycrystalline LiTaO₃ aggregates. We have found that LiTaO₃ in both phases has an indirect energy band gap. The differences in the electronic structure and density of states for both phases are quite small. Our results indicate that the mechanical and bonding properties of both phases are very similar. The obtained results were compared with the available experimental and theoretical values.     

A photonic crystal fiber sensor based on differential optical absorption spectroscopy for mixed gases detection

A photonic crystal fiber sensor based on differential optical absorption spectroscopy for mixed gas detection is presented. In such sensor, hollow core photonic crystal fiber is utilized as gas cell and the feasibility for gas detection is verified by experiment. The components concentration of mixed gas NH₃ and C₂H₂ are measured and the detection sensitivity is 143 ppmv.     

Frequency Doubling of a Laser Diode Using a Domain-Inverted LiTaO3Waveguide with a Monolithic Bragg Reflector

We report wavelength stabilization of a laser diode using a highly efficient distributed Bragg reflector (DBR) grating formed on a LiTaO₃ quasi-phase-matched second harmonic generation (QPM-SHG) device. Fabricating the second-order DBR on the LiTaO₃ waveguide, the reflectivity of 90% and FWHM wavelength bandwidth of 0.2 nm were obtained. By stabilizing the oscillation wavelength of the laser diode, 3.1 mW of blue light was generated in the QPM-SHG device with the monolithic grating.     

Multiple quantum NMR transitions of8Li (T 1/2=0.84 s) in single crystals and powders of LiTaO3, and the quadrupole moment of8Li

Multiple quantum nuclear magnetic resonance (NMR) transitions were observed on polarized⁸Li nuclei, which were produced by capture of polarized neutrons in a single crystal of LiTaO₃. The asymmetric⁸Liβ-radiation distribution was used for the detection of NMR. A quadrupole moment ratio ¦Q(⁸Li)/Q(⁷Li)¦=0.78(1) was determined. Saturation of multiple quantum transitions in nuclear radiation detected NMR may lead to a reduction in measuring time of up to two orders of magnitude, as compared to single quantum detection methods. The measured spectra agree well with an exact lineshape calculation. The same measurements were also performed on a LiTaO₃ powder sample. This was done to test a method to obtain quadrupole coupling constants from high field NMR multiple quantum powder patterns, which are easily detectable, also for higher nuclear spins. This latter method may be applicable also to conventional NMR detection techniques.     

An optical spectroscopy study of defects in lithium tantalate single crystals

The congruent, stoichiometric, and Mg doped stoichiometric LiTaO₃ single crystals have been successfully grown by the Czochralski technique. The evolution of defect structures caused by varying composition and post-growth processing has been evaluated from the optical absorption and photoluminescence measurements. Optical absorption studies showed that the UV absorption edge is very sensitive to the composition of LiTaO₃ crystals. Photoluminescence of various LiTaO₃ single crystals at room temperature was observed. The emission bands centered at 360, 430, and 530 nm were assigned to different defects, which can well show the defect information in LiTaO₃ crystals.     

Three-Layer Detection Pixel of Single-Photon Thermoelectric Detector Based on Rare-Earth Hexaborides

The results of computer simulation of heat propagation processes in the three-layer detection pixel of single-photon thermoelectric detector after the absorption of single photons with the energies 0.5–4.13 eV are presented. The various geometries of the detection pixel consisting of rareearth hexaborides are considered. The lanthanum hexaboride (LaB₆) is chosen as the absorber material, and for the materials of thermoelectric sensor the cerium (CeB₆) and lanthanum–cerium (La_0.99Ce_0.01) B6 hexaborides are chosen. The problem is solved to achieve the high system efficiency of thermoelectric detector for the detection of photons in the wavelength range from the UV to the near IR. The computer modeling was carried out based on the equation of heat propagation from the limited volume with the use of three-dimensional matrix method for differential equations. It is shown that a single-photon thermoelectric detector with a three-layer detection pixel made only of hexaborides will have the gigahertz count rate, high-energy resolution, and detection efficiency exceeding 90%. Taking into account the advantages of the three-layer detection pixel compared to the single-layer it can be argued that the three-layer detection pixel of the thermoelectric detector has the great prospects to solve a number of single-photon detection tasks.     

Large Size of Real-Time Bi12Si020 Hologram Device Made with Inexpensive Wafer Cutting Method

The large real-time hologram device made by the previous Bi₁₂SiO₂₀ single crystal wafer cutting method poses several problems such as a large residue of material hinders the practical use. A study was carried out to fabricate a real-time hologram device using inexpensive laterally cut circular (1 0 0) Bi₁₂SiO₂₀ single crystal wafers which would be suitable for practical use for 3-dimensional display. An angle incident on a (1 0 0) wafer is applicable to the real-time hologram. An optimal electrode design for a device with uniform diffraction efficiency was considered, and the device properties were experimentally investigated.     

强冲击压缩下LiF，Al2O3和LiTaO3单晶的透光性

在二级轻气炮上，用高速电子相机扫描照相技术和改进的Mallory实验装置，对z切LiF，Al₂O₃(蓝宝石)和LiTaO₃单晶材料的冲击透光性进行了对比测量，并用黑密度计提取出动态图像定量化的光强对比度变化曲线.结果表明，LiF单晶在102 GPa压强下能够保持长时间的初始透光性不变，与公认的LiF具有优良的高压下透明性的认识一致.LiTaO₃单晶在实验压力(139GPa)下变成基本不透明.而Al_{关键词： 2}O₃')" href="#">Al₂O₃ LiF 3')" href="#">LiTaO₃ 光学透明性     

Second-order nonlinear optical materials for efficient generation and amplification of temporally-coherent and narrow-linewidth terahertz waves

We have considered forward and backward optical parametric oscillation and amplification, and difference-frequency generation for efficiently generating and amplifying terahertz waves in several second-order nonlinear optical materials. We have used a single crystal of CdSe as an example. We have also investigated GaSe, periodically-poled LiNbO₃ and LiTaO₃, and diffusion-bonded-stacked GaAs and GaP plates. The advantage of using birefringence in CdSe and GaSe is tunability of the output terahertz frequency. Furthermore, both CdSe and GaSe can be used to achieve the backward parametric oscillation without any cavity. On the other hand, in periodically-poled LiNbO₃ and LiTaO₃, one can take advantage of large diagonal elements of second-order nonlinear susceptibility tensor. In the diffusion-bonded-stacked GaAs and GaP plates, quasi-phase matching can be achieved by alternatively rotating the plates. We have shown that it is feasible to achieve forward optical parametric oscillation in the THz domain using these plates. The advantage of using coherent parametric processes is possibility of efficiently generating and amplifying temporally-coherent and narrow-linewidth terahertz waves. Compared with a noncollinear configuration, by using the parallel wave propagation configurations, the conversion efficiency can be higher because of longer effective interaction length among all the waves.     

F2 laser induced oxidation of inorganic material

Transparent SiO₂ thin films were selectively fabricated on Si wafer by 157 nm F₂ laser in N₂/O₂ gas atmosphere. The F₂ laser photochemically produced active O(¹D) atoms from O₂ molecules in the gas atmosphere; strong oxidation reaction could be induced to fabricate SiO₂ thin films only on the irradiated areas of Si wafer. The oxidation reaction was sensitive to the single pulse fluence of F₂ laser. The irradiated areas were swelled and the height was approximately 500-1000 nm at the 205-mJ/cm² single pulse fluence for 60 min laser irradiation. The fabricated thin films were analytically identified to be SiO₂ by the Fourier-transform IR spectroscopy. The SiO₂ thin films could be also removed by subsequent chemical etching to fabricate micro-holes 50 nm in depth on Si wafer for microfabrication.     

Frequency doubling of wavelength locked laser diOde with a transmission-type filter in a confocal optical configuratiOn

Direct frequency doubling of a wavelength locked laser diode with an optical bandpass filter in a confocal optical configuration is demonstrated. The wavelength of the laser diode was locked in single longitudinal mode oscillation and tuned to phase-matching wavelength of a quasi-phase-matched second harmonic generation device based on a LiTaO₃ Waveguide. Stable blue light of 4.2 mW was obtained for incident power of 48 mW.     

Rapid thermal processing of lithium tantalite thin films prepared by a diol-based sol–gel process

Lithium tantalite (LiTaO₃) thin films have been deposited on Pt(111)/SiO₂/Si(100) substrates by means of sol–gel spin-coating technology. Using a diol-based precursor solution and rapid thermal processing (RTP), highly c-axis oriented LiTaO₃ thin films are obtained and the degree of orientation is increased with an increase of the heating rate. By changing the heating rate (600–3000 °C/min) and heating temperature (500–800 °C), the effects of various processing parameters on the growth of films are investigated. With the increase of heating rate, the grain size of LiTaO₃ thin films decreases markedly, and the relative dielectric constant (_r) increases from 28 up to 45.6. It was found that the dielectric loss factor (cos) decreased, and the ferroelectric properties were improved by the increase of heating rate. The figures of merit (F_v and F_m) indicate that the LiTaO₃ thin film with a heating rate of 1800 °C/min is suitable for application as a high-performance pyroelectric thin-film detector. PACS 81.20.Fw; 81.40.-z; 61.10.Eq; 77.84.-s     

Highly sensitive and selective trimethylamine sensors based on WO3 nanorods decorated with Au nanoparticles

One-dimensional tungsten oxide (WO₃) gas sensing materials have been widely used for the detection of trimethylamine (TMA) gas. Furthermore, it is believed that an effective method to improve the gas sensing performance is to introduce noble metals into sensing materials. In this work, a novel gas sensing material was prepared by decorating Au nanoparticles on WO₃ nanorods. Based on field emission scanning electron microscopy (FESEM/EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM), the morphology and microstructure of as-prepared samples were characterized. Results show that Au nanoparticles with diameter of 13–15 nm are loaded on the surface of WO₃ nanorods with length of about 1–2 µm and width of 50–80 nm. Gas sensing tests reveal that the Au@WO₃ sensor has remarkably enhanced response to TMA gas compared with pure WO₃ nanorods. In addition, and the gas sensing mechanism has been investigated based on the experimental results. The superior sensing features indicate the present Au@WO₃ nanocomposites are promising for gas sensors, which can be used in the detection of the trimethylamine gas and this work provides insights and strategies for the fabrication of sensing materials.     

基于红外光谱技术的混合气体检测系统概述

为了给从事红外混合气体检测领域的研究人员提供一定的借鉴与参考,针对红外混合气体检测系统中的光学复用结构以及检测方法进行了详细评述。目前,以量子级联激光器(QCL)、带间级联激光器(ICL)为代表的相干光源已逐渐取代热辐射红外光源、红外发光二极管(LED)等传统非相干光源,成为红外混合气体检测中的主流光源。相应地,具有超高探测度和极短响应时间的红外光探测器也逐渐超越以往的红外热探测器,占据红外探测器领域的主导地位。基于“复用思想”的光学复用结构则是红外混合气体检测系统的核心,主要包括单光源复用检测结构和多光源复用检测结构。其中,单光源复用检测结构以其体积小、集成度高等优点成为构建便携式混合气体检测系统的重要选择;而多光源复用检测结构是时分复用、频分复用、波分复用等思想的具体化,并凭借其较宽的光谱覆盖范围、较高的光谱分辨率等优势成为当前混合气体检测系统中的主导结构。应用于红外混合气体检测的检测方法主要有非分光红外(NDIR)光谱技术、波长/频率调制光谱技术、腔增强光谱技术以及光声光谱技术等。研究人员可通过对红外混合气体检测系统各组成部分充分了解后,设计出实用的红外混合气体检测系统,对工农业生产、环境监测、生命科学等诸多领域都具有重要意义。     

基于钽酸锂晶体的太赫兹波参量振荡器运转特性的研究

基于晶格振动模受激电磁耦子散射过程的基本原理,对由LiTaO₃（LT）晶体组成的太赫兹波参量振荡器（TPO）的输出调谐特性、增益和吸收损耗特性,以及基于硅棱镜阵列耦合装置的THz波输出特性等方面进行了详细的理论研究和分析.研究结果表明,基于LiTaO₃晶体A₁对称性晶格振动的特点以及自身优异的非线性光学特性,通过利用短波长抽运光、适当提高抽运能量以及缩短TPO谐振腔腔长等方法,完全可以实现LT-TPO的高性能运转,证明了LiTaO₃晶体是一种性能优良的TPO工作介质.理论计算结果及方法为以后的LT-TPO实验工作提供了详实的理论依据和实验指导. 关键词： 非线性光学 THz辐射 3晶体')" href="#">LiTaO₃晶体 电磁耦子