调谐半导体激光光谱分时扫描多路方法

针对调谐半导体激光光谱多组分气体检测需要,提出了一种基于多激光分时扫描的激光时分多路新方法.该方法结合了波长调制光谱技术,通过对多台检测激光器输出波长的分时扫描,在一个系统周期内实现多组分气体的准同时检测.将该方法应用于天然气泄漏红外激光多组分检测系统,通过对天然气主要成份CH4和H2S的同时测量,及时发现可能的天然气气体泄漏,在满足灵敏检测的前提下,实现了系统结构的简化.     

基于光谱分析方法的光引发剂量子效率评估

基于光谱学和Beer-Lambert定律,提出了一种评估光引发剂量子效率的新模型和方法,并给出了有关的理论分析.研究通过增加曝光厚度的方法,测定了光引发剂1173(HMPP)曝光过程中的吸收光谱,根据吸收光谱的特征峰值随曝光时间的变化速率与评估模型,获得相应的量子效率.研究结果表明:光引发剂1173在247 nm和285 nm处存在两个吸收峰;主吸收峰(247 nm)的量子效率为0.278%;实验结果与理论分析一致.     

紫外吸收光谱法研究硝酸盐溶液

分析硝酸盐溶液的紫外吸收光谱,对于人类健康、环境治理等问题具有重要意义。水中氮含量超过一定标准,会造成水体富营养化,引起水体污染,水质开始恶化,并伴有腥臭味,对人体健康非常不利。实验表明,硝酸盐溶液的紫外吸收光谱谱线在200—240nm内具有明显的吸收峰,浓度处于1—7mg/L之间,吸光度正比于溶液浓度。在200—240nm范围内确定了线性程度最好的波长点为220nm。经过一元线性回归建模,获得220nm处的回归直线关系式,它的相关系数为0.9974,回归系数的标准误差分别为0.022307和0.005152。整个结果为水中氮测定及其特性研究、光电检测提供了科学参考。     

N-邻羟基萘甲酰胺基-N′-苯基硫脲的合成及其对阴离子的识别

设计合成了3种N-邻羟基萘甲酰胺基-N′-苯基硫脲类化合物,通过核磁共振谱和质谱表征了其结构。应用吸收光谱和荧光光谱考察了在乙腈中其与F-、CH3CO2-、H2PO4-、HSO4-、Cl-和Br-等阴离子的相互作用。结果表明,该类主体分子与阴离子形成结合比为1∶1氢键配合物,通过改变萘环上酰基和羟基的相邻位置可调控识别作用的选择性,它们与阴离子作用分别在355、367nm和372nm出现最大吸收峰,荧光光谱显示它们对F-有突出的响应灵敏度,可选择性识别F-。     

Electronic band structure and optical properties of silicon nanoporous pillar array

Silicon nanoporous pillar array (Si-NPA) is fabricated by hydrothermally etching single crystal silicon (c-Si) wafers in hydrofluoric acid containing ferric nitrate. Microstructure studies disclosed that it is a typical micron/nanometer structural composite system with clear hierarchical structures. The optical parameters of Si-NPA were calculated by general light-absorption theory and Kramers–Kronig relations based on the experimental data of reflectance and the variations compared with the counterparts of c-Si were analyzed. The features of the electronic band structure deduced from the optical measurements strongly indicate that Si-NPA material is a direct-band-gap semiconductor and possesses separated conduction sub-bands which accords with conduction band splitting caused by silicon nanocrystallites several nanometers in size. All these electronic and optical results are due to the quantum confinement effect of the carriers in silicon nanocrystallites.     

Ab initio calculations of electronic structures of SrMoO4 crystals containing F and F color centers

The electronic structures of SrMoO₄ crystals containing F and F⁺ color centers with the lattice structure optimized are studied within the framework of the fully relativistic self-consistent Dirac–Slater theory, using a numerically discrete variational (DV-Xα) method. From the calculation, it is concluded that F and F⁺ color centers have donor energy level in the forbidden band. The electronic transition energies from the donor level to the bottom of the conduction band are 1.855 eV and 2.161 eV, respectively, which correspond to the 670 nm and 575 nm absorption bands. It is predicted that the 670 nm and 575 nm absorption bands originate from the F and F⁺ centers in SrMoO₄ crystals.     

Peculiarities of photoluminescence excited by 157 nm wavelength F2 excimer laser in fused and unfused silicon dioxide

Photoluminescence (PL) spectra and kinetics of high purity amorphous silicon dioxide with ultra low hydroxyl content is studied under the excitation by F₂ excimer laser (157 nm wavelength) pulses. Materials synthesized in the SPCVD plasma chemical process are studied before and after fusion. Two bands are found in the PL spectra: one centered at 2.6–2.9 eV (a blue band) and the other at 4.4 eV (a UV band). Luminescence intensity of unfused material is found to increase significantly with exposure time starting from a very small level, whereas in fused counterpart it does not depend on irradiation time. Both bands show complicated decay kinetics, to which add exponential and hyperbolic functions. The UV band of the unfused material is characterized by decay with exponential time constant τ  4.5 ns and hyperbolic function t⁻ⁿ, where n = 1.5 ± 0.4. For the blue band the hyperbolic decay kinetics with n  1.5 extends to several milliseconds, gradually transforming to the exponential one with τ = 11 ± 0.5 ms. In fused glass relative contribution of the fast component to the UV band is small whereas for the blue one it is great, that allows one to more accurately determine the hyperbolic law factor n = 1.1 ± 0.1 typical for tunneling recombination. Simultaneous intracenter and recombination luminescence, the later occurring with the participation of laser radiation induced defects, add particular features to the decay kinetics. Spectra of the above luminescence processes are different. A less sharp position of bands is associated with the recombination luminescence. The origin of the observed PL features we attribute to the presence of oxygen deficient centers in glass network in the form of twofold coordinated silicon. Such centers being affected by network irregularities can be responsible for the recombination PL component. A great variety of network irregularities is responsible for centers’ structural inequivalence, which causes a non-uniform broadening of PL spectral and kinetic parameters.     

Absorption and photoluminescence of PbS QDs in glasses

Optical properties of PbS quantum dots (QDs) precipitated inside the oxide glass matrix were investigated. Photoluminescence (PL) from the PbS QDs showed peak wavelengths located at 1170–1680 nm with widths of 150–550 nm. Radii of QDs in glasses were 2.3–4.7 nm depending upon the thermal treatment. Peak wavelengths of PL bands shifted as much as 70 nm as the temperatures and excitation irradiances increased. Calculated effective local temperatures indicated that these shifts of PL spectra were associated with local heating induced by the temperatures and laser beam.     

An IH-QCL based gas sensor for simultaneous detection of methane and acetylene

Extended wavelength tuning of an IH-QCL (integrated heater quantum cascade laser) is exploited for simultaneous detection of methane and acetylene using direct absorption spectroscopy. The integrated heater, placed within few microns of the laser active region, enables wider wavelength tuning than would be possible with a conventional DFB (distributed feedback) QCL. In this work, the laser current and heater resistor current are modulated simultaneously at 25?kHz to tune the laser over 1279.6–1280.1 cm^?1, covering absorption transitions of methane and acetylene. The laser is characterized extensively to understand the dependence of wavelength tuning on modulation frequency, modulation amplitude and phase difference between laser/heater modulation. Thereafter, the designed sensor is validated in both room-temperature static cell experiments and non-reactive high-temperature-measurements in methane-acetylene-argon gas mixtures in the shock tube. Finally, the sensor is applied for simultaneous detection of methane and acetylene during the high-temperature pyrolysis of iso-octane behind reflected shock waves.     

A ppb level sensitive sensor for atmospheric methane detection

A high sensitivity sensor, combining a multipass cell and wavelength modulation spectroscopy in the near infrared spectral region was designed and implemented for trace gas detection. The effective length of the multipass cell was about 290 meters. The developed spectroscopic technique demonstrates an improved sensitivity of methane in ambient air and a relatively short detection time compared to previously reported sensors. Home-built electronics and software were employed for diode laser frequency modulation, signal lock-in detection and processing. A dual beam scheme and a balanced photo-detector were implemented to suppress the intensity modulation and noise for better detection sensitivity. The performance of the sensor was evaluated in a series of measurements ranging from three hours to two days. The average methane concentration measured in ambient air was 2.01 ppm with a relative error of ± 2.5%. With Allan deviation analysis, it was found that the methane detection limit of 1.2 ppb was achieved in 650 s. The developed sensor is compact and portable, and thus it is well suited for field measurements of methane and other trace gases.