基于激光吸收光谱技术的超声速气流参数测量

采用可调谐半导体激光吸收光谱(TDLAS)技术,针对超声速直连台隔离段内超声速气流温度、组分浓度、速度和质量流量进行了测量.选择H2O的两条吸收谱线7 185.597 cm-1和7 454.445 cm-1,采用直接吸收-分时扫描方式,测量流场静温为899 K,并结合吸收面积得到H2O的组分浓度20.7%.根据安装在流场上游和下游成60的两条光路,测量流场速度为1 205 m/s,结合壁面压力传感器,测量流场的质量流量为1 500.49 g/s,较真实值偏差为5.23%.TDLAS测量系统实现了对超声速气流多参数快速线测量.     

基于TDLAS的气体温度测量

介绍了基于可调谐半导体激光吸收光谱(TDLAS)的气体温度测量原理,选择了1对O2吸收谱线13 163.78 cm-1和13 164.18 cm-1,理论计算了此谱线对线强比值R与温度的关系,在搭建的高温实验装置上实现了O2温度和浓度的同时测量,并分析了压力对温度测量的影响。实验结果表明:在823~1 323 K内,温度测量的线性误差为0.65%。最大波动为±15 K,压力变化对温度测量的影响可忽略不计。     

基于TDLAS技术1.65μm附近乙烷分子高分辨吸收光谱测量

基于可调谐半导体激光光谱(TDLAS)技术,结合实验室自制程长可达50 m的Herriot池,使用波长计对乙烷吸收谱线进行了准确定标,并根据记录的光谱数据,精确测量了6039～6054 cm-1波段内71条乙烷分子的谱线(中心位置及谱线强度),最小可探测谱线吸收强度为10-25 cm-1/(molecule·cm-2),对结果及误差进行了详细分析,为进一步研究天然气提供了重要参考.     

TDLAS燃烧气体温度测量吸收谱线对的选择

高温气体的温度场测量,一直以来是一项重大科研课题,而利用可调谐二极管激光吸收光谱法(TDLAS)测量燃烧气体温度的基础是吸收谱线对的选择。本文首先系统地给出吸收分子及其谱线对的选择标准,而后重点对HITEMP数据库中1547.72 nm附近的水分子吸收谱线进行研究与筛选,通过仿真分析验证了谱线对6460.595 cm-1和6461.271 cm-1适合用于TDLAS高温气体温度测量系统,最后通过搭建的实验设备验证了这一对吸收谱线对很适合用作氢气或碳氢化合物做燃料的高温气体的温度测量,对TDLAS温度场测量系统的设计具有参考意义。     

基于MATLAB洛伦兹线型非线性拟合算法实现

可调谐半导体吸收光谱(TDLAS)技术具有高选择性、高分辨率和速度快等优点,已经在环境检测、工业过程检测等方面得到广泛应用.主要分析洛伦兹线型拟合,研究Levenberg-Marquardt算法的原理及实现步骤,基于Levenberg-Marquardt算法实现吸收谱线的洛伦兹线型拟合.对六组不同浓度的CO2标准气体进行浓度反演,反演浓度与实际浓度的相关系数达0.9928,表明洛伦兹线型拟合可以准确反演出气体的浓度,对TDLAS技术中浓度的反演具有实际的指导意义.     

基于TDLAS技术的空气气压精确测量

基于可调谐激光二极管吸收光谱(TDLAS)技术,通 过测量水汽吸收线的展宽,实现了气体压力的精确测量。实验中光源被 分为两束,一束通过压力可调的样品池获得吸收光谱数据,另一束通过FP标准具用以波 长定标。选取 水汽在7243cm－1附近的两条吸收线, 利用测得的10～20kPa之间的水汽吸收线压力展宽值对 HITRAN数据库中的空气展宽系数进行校正。实时测量了参考气压值从30～100kPa时的 水汽吸收线压力展宽,计算得到气压值并与参考气压进行比较,不同参考压力下利用水汽7243.075cm－1 和7242.370cm－1处吸收峰计算结果与参考气压值的偏差分别分布于0.9%附近和2.0%附近,两条吸收谱线 测量结果波动均小于0.2%。实验测量结果与参考值几乎一致,且同一条件不同次测量结果波 动较小,证明了TDLAS技术应用于实时环境气压精确快速测量的可行性。     

可调谐二极管激光光谱技术测量燃烧环境下H2O浓度的实验设计

水蒸气是碳氢化合物燃烧的主要产物之一,对其浓度进行测量具有重要的意义.在已有理论基础上推导选择了最佳的拟合线型函数(Voigt线型),结合HITRAN数据库选择了在实验室现有条件下理想的吸收线.理论分析了用两条相邻吸收线的线强比计算温度的可行性,在此基础上建立了一套基于可调谐二极管激光吸收光谱(TDLAS)技术的实验装置,为进一步实验打下了良好的基础.     

可调谐半导体激光吸收传感器的温度测量验证

开发了一种可调谐半导体激光吸收传感器,用于测量气体的温度,应用扫描波长吸收谱和固定波长调制谱探测水蒸气在7 454.4 cm-1和7 185.6 cm-1附近的两条吸收谱线。传感器可实现绝对温度测量,固定波长调制谱更可实现10 kHz以上的测量带宽。传感器的性能和精度在已知温度和压力的静室中进行测量验证,在600~1 000 K的设定温度范围,两种方法的测量误差（RMS）都小于2%。表明可调谐半导体激光吸收光谱（TDLAS）传感器对于均匀的流场具有快速和精确的温度测量能力。     

可调谐二极管激光吸收光谱技术测量风洞流速

基于对水蒸气的吸收谱线在超音速流场的多普勒效应,结合HITRAN数据库,选取适合当前环境的吸收谱线7181.1558 cm-1,结合超音速风洞装置建立起一套基于可调谐二极管激光吸收光谱(TDLAS)技术的实验装置,测量对应频移,分析反演出流场速度,实验结果表明,在高速环境下,系统测量流速为563.06 m/s,线性误差为5.09%,效果良好,从而为对激波管等高速脉冲设备的进一步测量实验打下了良好基础。     

基于TDLAS一次谐波的二氧化碳温度测量

为了实现二氧化碳气体温度的实时、非接触测量,研究基于可调谐二极管激光吸收光谱技术(TDLAS)的温度测量方法。根据单激光器的电流调谐特性和谱线对的选择标准,选取6241.402828 cm-1、6242.672190 cm-1处的两条对温度有不同依赖关系的二氧化碳谱线进行分析。针对二次谐波幅度法和一、二次谐波幅度比值法所存在的问题,提出应用一次谐波信号的TDLAS温度测量方案。首先测量两吸收谱线的一次谐波峰峰值和平均值,以峰峰值和平均值的比值作为单吸收线的输出,再以两吸收线输出值之比来实现气体温度的测量。实验结果表明:在200~1000K范围内,气体温度测量误差小于30 K。该温度测量方案可消除光强波动对温度测量产生的影响,且仅需检测一次谐波信号,系统结构简单,性能稳定,可以满足二氧化碳气体温度实时、非接触测量的需要。     

A comparison of optoelectronic properties of lattice-matched andstrained quantum-well and quantum-wire structures

The k·p formalism is used to study the absorption spectra, material and differential gain in quantum wires as a function of orientation, built-in strain, and wire dimensions. The results for material and differential gain are compared with those for an optimized quantum-well structure. We find that for quantum wires at 300 K, the gain becomes positive at a carrier density of 1.27·10¹⁸ cm^-3, while in quantum wells this density is calculated to be 1.82·10¹⁸ cm^-3. Incorporating tensile strain in the wires reduces the transparency carrier concentration to 0.96·10¹⁸ cm^-3 while compressive strain allows one to obtain positive gain for densities greater than 1.08·10¹⁸ cm^-3. Orienting the wire along the [111] direction reduces the transparency carrier density to 0.60·10¹⁸ cm^-3. The differential gain in quantum-well structures for injections near the threshold is on the order of 10^-14 cm^-4, while for 50 Å·100-Å quantum wires the differential gain near the threshold is found to be on the order of 10^-13 cm^-4 . The differential gain in wires whose wire axis is parallel to the [111] direction has also been found to be on the order of 10^-13 cm^-4 for carrier injections close to the threshold     

Continuously tunable high-pressure CO2 laser forspectroscopic studies on trace gases

A high-pressure CO₂ laser with unique characteristics in terms of continuous tunability and emission bandwidth is presented. It is operated at a pressure of 11.5 bar and transversely excited by short, high-voltage pulses generated by a double LC inversion circuit. Auxiliary discharges parallel to the electrodes provide a sufficient free-electron density through UV ionization of the laser gas mixture. The laser resonator consists of a near-grazing-incidence grating setup in which the grating is positioned at a large incidence angle of 77°. A theoretical model for the calculation of the emission bandwidth is presented and its predictions are compared to direct measurements and show excellent agreement. The achieved very narrow bandwidth of 0.018 cm^-1 constitutes the ultimate wavelength resolution of any detection system using this laser as radiation source. It allows the resolution of any fine structure in the spectra of absorbing gases at atmospheric pressure. Continuous tunability has been achieved over 76 cm^-1 between 932 cm^-1 and 1088 cm ^-1 with minimum pulse energies in excess of 10 mJ. The narrow bandwidth precludes the occurrence of mode-pulling effects so that the laser exhibits a linear wavelength tuning behavior throughout the entire emission range. The calibration of the laser wavelength is performed by photoacoustic measurements on low pressure CO₂ gas. An absolute accuracy of ±10^-2 cm^-1 is achieved. A great potential improvement in detection selectivity can thus be expected from a scheme with the high-pressure CO₂ laser as radiation source     

The effect of intervalence band absorption on the thermal behavior of InGaAsP lasers

Measurements of intervalence band absorption spectra were made in p-type In0.53Ga0.47As, InP, and GaAs. The measured spectra are broader, have less temperature dependence, and have 2× less peak intensity than theoretical curves predicted by an elementarykcdotpband model. Forp = 10^{18}cm^-3, all three crystals have absorption coefficients of about 13 cm^-1at 1.3 μm and 25 cm^-1at 1.6 μm. These values of absorption should also be applicable as estimates of intervalence band absorption in quaternary laser material. Because of the low strength and weak temperature dependence of the intervalence band absorption, it should have only a minor effect on the temperature dependence of laser threshold. For example, using our absorption data, we calculate that intervalence band absorption will reduce the experimental temperature parameter T0of 1.3 μm quaternary lasers from 194 to 179 K.     

Power optimization of small-scale chemical oxygen-iodine laser withjet-type singlet oxygen generator

Studies of power optimization of a 5-cm gain length chemical oxygen-iodine laser (COIL) energized by a jet-type singlet oxygen generator (JSOG) are presented. For 10 mmol/s of Cl₂ flow rate, output power of 132 W with chemical efficiency of 14.5% was obtained without a water vapor trap, 163 W and 18% were achieved when coholed (173 K). He was introduced downstream of the JSOG; under these conditions, the small-signal gain was estimated to be 0.32% cm^-1 . 190 W and 10.5% were obtained for 20 mmol/s of CI₂ flow rate. Replacing He by N₂ as a buffer gas resulted in a 13% power decrease only. The main key for increasing the chemical efficiency of a COIL without a water vapor trap for a given iodine-oxygen mixing system is found to be high oxygen pressure and low water vapor pressure inside the reaction zone of the JSOG. The last goal was achieved by optimizing the composition and temperature of the basic hydrogen-peroxide solution (BHP). The experimental results are discussed and related to the composition and flow conditions of the gaseous reactants and of the BHP     

High quality SiO2/Si interfaces of poly-crystallinesilicon thin film transistors by annealing in wet atmosphere

A new post-metallization annealing technique was developed to improve the quality of metal-oxide-semiconductor (MOS) devices using SiO ₂ films formed by a parallel-plate remote plasma chemical vapor deposition as gate insulators. The quality of the interface between SiO₂ and crystalline Si was investigated by capacitance-voltage (C-V) measurements. An H₂O vapor annealing at 270°C for 30 min efficiently decreased the interface trap density to 2.0×10¹⁰ cm^-2 eV^-1, and the effective oxide charge density from 1×10 ¹² to 5×10⁹ cm^-2. This annealing process was also applied to the fabrication of Al-gate polycrystalline silicon thin film transistors (poly-Si TFT's) at 270°C. In p-channel poly-Si TFT's, the carrier mobility increased from 60-400 cm² V^-1 s^-1 and the threshold voltage decreased from -5.5 to -1.7 V     

The influence of single-photon absorption on the performance of thetwo-photon waveguide autocorrelator

The propagation loss and the single-photon absorption coefficients in a two-photon waveguide autocorrelator are measured as a function of wavelength. The propagation loss was as low as 1.37 cm^-1 at a wavelength of 940 nm in a device with an Al_0.2Ga_0.8As waveguide core. Using a photocurrent technique, band-to-band absorption was measured for photon energies well below that of the bandgap. It was demonstrated that, although the band-to-band absorption coefficient is small (~10^-2 cm^-1 at a wavelength of 1 μm), it is responsible for reducing the contrast ratio of the waveguide autocorrelator. It is suggested that the single-photon absorption takes place via deep levels with relatively long carrier lifetimes     

Characterization of the Ultrathin HfO2 and Hf-Silicate Films Grown by Atomic Layer Deposition

The physical properties of HfO₂ and Hf-silicate layers grown by the atomic layer chemical vapor deposition are characterized as a function of the Hf concentration and the annealing temperature. The peaks of Fourier transform infrared spectra at 960, 900, and 820 cm_-1 originate from Hf-O-Si chemical bonds, revealing that a Hf-silicate interfacial layer began to form at the HfO₂/SiO ₂ interface after post deposition annealing process at 600 degC for 1 min. Moreover, the intensity of the peak at 750 cm^-1 can indicate the degree of crystallization of HfO₂. The formed Hf-silicate layer between HfO² and SiO² is also confirmed by X-ray photoelectron spectroscopy     

基于室温脉冲量子级联激光器的大气N2O监测仪研制

介绍了一种基于室温脉冲量子级联激光器的大气N2O监测仪的研制,以中心波长为1274cm-1的分布反馈式量子级联激光器为光源,结合长光程多次反射池,可实现对大气中N2O的测量.该系统利用激光器长脉冲产生的线性频率啁啾,扫描通过气体分子完整的吸收线,从而进行定性和定量分析.集成的数据分析软件根据HITRAN04数据库中的谱线参数采用直接吸收的方法对气体进行测量,不需要定标,系统具有良好的重复性和稳定性,检测限低于13 ppb,可实现大气中N2O的检测.     

KrF excimer laser annealed TFT with very high field-effect mobilityof 329 cm2/V-s

A thin-film transistor (TFT) with a maximum field-effect mobility of 320 cm²/V-s, an on/off current ratio of 7.6×10⁷ , a threshold voltage of 6.7 V and a subthreshold slope of 0.37 V/decade was fabricated by using pulse laser annealing processes. Amorphous silicon films (a-Si:H) with a very low impurity concentration of 4×10¹⁸ cm^-3 for oxygen, 1.5×10¹⁸ cm^-3 for carbon, and 2×10¹⁷ cm^-3 for nitrogen were deposited by a plasma chemical vapor deposition (CVD) method and annealed by KrF excimer laser (wavelength of 248 nm). The Raman spectroscopy technique was a useful tool for optimizing laser annealing conditions. Experimental results show that two factors are very important for fabricating very-high mobility TFTs: (1) utilizing high-purity as-deposited a-Si:H film; and (2) performing whole laser annealing processes sequentially in a vacuum container and optimizing illumination conditions     

Rapid thermal chemical vapor deposited oxides on N-type 6H-siliconcarbide

The electrical characteristics of oxides deposited on nitrogen doped N-type 6H-silicon carbide using rapid thermal chemical vapor deposition are reported. The gases used in the deposition process were silane (diluted with argon), and nitrous oxide. The oxide was found to have an interface state density of 7×10¹¹ cm^-2 eV^-1 and a low effective charge density of 1.1×10 ¹¹ cm^-2. The deposited oxide is compared with oxide grown thermally on N-type 6H-silicon carbide by wet oxidation. The quality of the deposited oxide is found to be comparable to the quality of the thermal oxide. An excellent low thermal budget process to obtain good oxides on N-type 6H-silicon carbide has thus been demonstrated for the first time