基于双共振吸收光谱法的~(14)CO_2探测（英文）

快速且准确地定量探测~(14)CO_2在许多领域都有着重要应用.超灵敏的光腔衰荡光谱技术是一种极具潜力的光学探测方法,但其存在灵敏度不足和易受其他CO_2同位素/杂质分子干扰的问题.本文提出利用阶梯型双共振光谱法将~(14)CO_2从基态激发至中间能级后,再用光腔衰荡光谱法去探测.双共振的吸收过程可以有效提高探测的选择性.本文分析了双共振吸收光谱的定量探测能力,模拟结果显示双共振光谱探测是无多普勒的,可以减少其他分子的吸收干扰,有望实现亚ppt水平的~(14)CO_2高选择性探测.     

CO2对790 nm附近水线的压力加宽和位移

采用高灵敏的激光光腔衰荡光谱技术研究了CO₂对¹⁶O水分子v²+3v³振动带跃迁线的压力诱导效应. 为了抑制水的自碰撞效应,水的压力在实验中低于0.5 Torr. 基于铷原子吸收线和超稳法布里-珀罗标准确定了跃迁谱线高达10^-5 cm^-1精度的绝对频率. 采用软碰撞模型对吸收线进行模拟,获得了对应的线形参数.     

C2H2 Overtones Near 12300 cm-1 Revisited with a Very Sensitive Cavity Ring-down Spectrometer

利用单模连续的钛宝石激光器, 构建了一台光腔衰荡光谱仪, 其可探测的最小吸收可达1.8×10^-10/cm. 该光谱仪被用来记录C₂H₂分子在12240～12350 cm^-1的泛频光谱. 与在同一波段测量的已报到的CRDS和激光腔内吸收光谱仪结果比较,本测量同时具有更好的灵敏度和精度. 由此,获得了乙炔分子在12290.12、12311.82和12350.61 cm^-1附近高泛频谱带更准确的振转参数     

Ti+(CO2)2Ar和Ti+(CO2)n(n=3-7)络合物离子的红外光解离光谱 (cited: 1)

利用脉冲激光溅射-超声分子束载带方法制备了气相Ti⁺(CO₂)₂Ar和Ti⁺(CO₂)_n(n=3-7)络合物离子．采用红外光解离光谱研究了这些选定的质量离子的振动光谱． 对于每一种络合物离子, 在CO伸缩振动频率范围都观察到了振动峰,表明这些离子具有插入的OTi⁺CO(CO₂)_n-1结构． 对于n≦5的OTi⁺CO(CO₂)_n-1离子,其CO振动和CO₂的反对称伸缩振动频率都比自由的CO和CO₂的频率要高,表明CO和CO₂配体与中心金属离子之间主要是静电相互作用．实验结果还表明TiO⁺可以直接络合五个配体(1个CO和4个CO₂分子)．对于n=2络合物体系,除了插入的OTi⁺CO(CO₂)结构以外,还观察到了具有弯曲结构的OCO-Ti⁺-OCO异构体的存在     

NO2分子的光学-光学双色双共振多光子离化谱

以Nd:YAG激光器的二倍频输出光为抽运光，其三倍频输出抽运的光学参量发生/放大器输出光为探测光，利用光学-光学双色双共振多光子离化光谱技术(OODR-MPI),获得了NO₂分子在605—675nm探测光波长范围内的多光子离化激发谱. 通过对NO₂分子离化机理的分析，确定了在此波长区间，NO₂分子经1+3+1双共振多光子过程离化，离化通道为NO₂(X²A₁)hν     

光腔衰荡光谱法测量大气中的NO3和N2O5

本文应用基于二极管激光器的双路光腔衰荡光谱技术,分别对大气中NO₃和N₂O₅浓度进行监测. 通过使用实验室标准样校正有效吸收腔长比R_L和系统的总损耗系数?,并获得了NO₃有效吸收截面. 该装置在时间分辨率为1 s时,对NO₃的测量灵敏度达到1.1 pptv,N₂O₅被在线转换成NO₃,从而被另一路光腔衰荡光谱装置探测. 利用该装置,对合肥市区冬季夜间大气中的NO₃,N₂O₅浓度进行了实时监测. 通过对比一次大气快速清洁过程中氮氧化物、臭氧、PM_2.5等组分的浓度变化,讨论了大气环境下可能影响NO₃及N₂O₅浓度的因素.     

线形C5H自由基A2Δ电子态的自选轨道分裂和寿命展宽

重新研究了C₅H和C₅D自由基A²Δ-X2Π电子吸收谱带. 利用乙炔/氦混合气脉冲直流放电产生的碳氢等离子体制备气相C5H和C5D自由基,利用光腔衰荡光谱记录碳氢等离子体束的直接吸收光谱. 与之前工作相比,实验光谱的波长校准得到了改进. 通过对实验光谱的分析,首次实验确定了C₅H自由基A²Δ电子态的自旋-轨道分裂常数为-0.7(3) cm^-1. 这为标识A2￠电子态的提供了有力的实验证据. 通过对谱带寿命展宽的分析,A²Δ电子态的寿命估测为1.6±0.3 ps.     

[Co(CO2)n]+团簇的红外解离光谱实验和理论研究

本文利用红外光解离光谱研究了一价钴阳离子与二氧化碳之间的相互作用. 通过密度泛函理论计算得到[Co(CO₂)_n]⁺团簇的几何结构,并且模拟了它们的振动光谱与实验数值进行比较. 研究结果表明,在[Co(CO₂)_n]⁺(n=2∽6)团簇中,钴阳离子通过电四极矩静电作用以端点结合的方式与二氧化碳中的氧原子结合在一起. 团簇的红外光谱都集中在二氧化碳反对称伸缩的波数附近,并且随着团簇尺寸的变化出现蓝移,最后把[Co(CO₂)_n]⁺的红外光解离光谱与稀有气体贴附的[Co(CO₂)_n]⁺-Ar的红外光解离光谱进行了比较.     

15N216O在1650-3450 cm-1的高分辨红外光谱

采用傅里叶变换红外光谱仪记录了富含¹⁵N₂¹⁶O同位素的一氧化二氮样品在1650-3450 cm^-1波段的高分辨振转光谱,得到了该同位素分子超过7300吸收谱线位置的实验值,经分析实验精确度好于5.0×10^-4 cm^-1. 基于有效哈密顿量模型预测和带带转动分析,确定了所有吸收线的归属;获得了29个新吸收带的振转光谱参数,并优化了其他44个吸收带的光谱参数值. 并且发现有效哈     

基于半导体激光的光腔衰荡光谱装置测定水汽含量

搭建了一套基于光腔衰荡光谱技术的光学湿度计. 通过测量水分子在1.35和1.56 μm波段不同强度的吸收线,可测定水汽的相对含量,测量范围从10^-2到低至10^-12水平. 通过与商用冷镜式露点仪的对比测量,对该装置的定量精度进行了检验. 该系统所具备的高灵敏度使得水汽探测极限可达8 pptv     

Frequency-stabilized cavity ring-down spectrometer for high-sensitivity measurements of water vapor concentration

We present a portable spectrometer that uses the frequency-stabilized cavity ring-down spectroscopy technique capable of high-precision measurements of trace water vapor concentration. Measuring one of the strongest rovibrational transitions in the ν₁+ν₃ water vapor combination band near ˜ν=7181.156 cm^-1, we compare spectroscopic and thermodynamic determinations of trace water vapor in N₂, and find systematic differences attributable to water vapor background effects and/or uncertainties in line intensities. We also compare the frequency-stabilized ring-down method with other cavity ring-down approaches that are based on unstabilized probe lasers and unstabilized ring-down cavities. We show that for the determination of water vapor concentration, the frequency-stabilized cavity ring-down method has the minimum measurement uncertainty of these techniques. The minimum noise-equivalent absorption coefficient of the spectrometer was 1.2×10^-10 cm^-1 Hz^-1/2, which further corresponds to a minimum detectable water vapor mole fraction equal to 0.7×10^-9 for an absorption spectrum of 10 minutes duration. PACS 33.20.-t; 33.70.Jg; 33.70.Fd; 42.62.Fi     

Study of gas detection based on integrated cavity output spectroscopy

A trace gases detection system based on integrated cavity output spectroscopy (ICOS) was developed, where a NIR tunable diode laser (TDL) was used as light source, an optical cavity composed by two plan-concave mirrors with reflection near 99.7% was used as the absorption cell. Trace water vapour (H₂O), carbon dioxide (CO₂), methane (CH₄), carbon monoxide (CO) and mixture of CO₂ and CO were tested by ICOS based on the characteristics absorption. The wavelength calibration, cavity transmission characteristics, quantitative measurement ability and sensitivity of the TDL-ICOS were also studied, and a evaluated minimum detectable sensitivity of 1.15 × 10^?7 cm^?1 was obtained when the system was used to CH₄ detection. The experiment results show that TDL-ICOS is expected to be a reliable and promising system for the detection of trace gases since it has some advantages such as real-time monitoring, simple device, easy operation, high sensitivity, good stability and quantitative ability.     

A calibration method for broad-bandwidth cavity enhanced absorption spectroscopy performed with supercontinuum radiation

An efficient calibration method has been developed for broad-bandwidth cavity enhanced absorption spectroscopy. The calibration is performed using phase shift cavity ring-down spectroscopy, which is conveniently implemented through use of an acousto-optic tunable filter (AOTF). The AOTF permits a narrowband portion of the SC spectrum to be scanned over the full high-reflectivity bandwidth of the cavity mirrors. After calibration the AOTF is switched off and broad-bandwidth CEAS can be performed with the same light source without any loss of alignment to the set-up. We demonstrate the merits of the method by probing transitions of oxygen molecules O₂ and collisional pairs of oxygen molecules (O₂)₂ in the visible spectral range.     

Pulsed cavity ring-down spectroscopy of NO and NO2 in the exhaust of a diesel engine

The application of pulsed cavity ring-down spectroscopy has been demonstrated for the in situ quantitative determination of NO and NO₂ in the exhaust of a diesel engine. NO absorption has been monitored at the transition from the Χ²Π ground state to the A²Σ⁺ state at 226 nm. For NO₂, absorption bands in the spectral region from 438 nm to 450 nm were used. At the selected engine conditions, concentrations of 212±22 ppm and 29±4 ppm have been measured for NO and NO₂, respectively, in good agreement with separate chemical exhaust gas analysis. The method is sensitive enough to meet the European Euro V standard directive on NO_x emissions. This communication discusses the relatively simple setup needed for this type of measurement, the problems encountered, as well as the prospects for single-stroke, simultaneous measurements of both NO and NO₂ at the sub-ppm level. Received: 30 November 2001 / Revised version: 18 February 2002 / Published online: 14 March 2002     

Quantum-noise-limited cavity ring-down spectroscopy

We demonstrate a heterodyne-detected cavity ring-down spectroscopy (CRDS) method that allows for a noise-equivalent absorption coefficient of 6 × 10^?14 cm^?1 Hz^?1/2, the lowest which has been reported in a CRDS measurement. It is shown that heterodyne-detected CRDS also reaches the quantum noise limit at reasonable optical powers. In addition to offering ultra-high sensitivity, this technique provides high frequency agility over a range of 2 THz in the near-infrared, which allows entire absorption bands to be recorded in minutes. As a demonstration experiment, high resolution spectra of a near-infrared carbon dioxide band have been recorded.     

Photon-trap spectroscopy of size-selected free cluster ions: “direct” measurement of optical absorption of Ag+ 9

An absorption spectrum of size-selected free cluster ions has been measured “directly” via extinction of light without relying on photodepletion/dissociation spectroscopy. The novel technique employs an ion trap and an optical cavity; cluster ions stored in an ion trap interact with photons trapped in a cavity. The storage lifetime of photons in the cavity provides “direct” observation of extinction of light (photon-trap spectroscopy, which is a generalized scheme of cavity ring-down spectroscopy). The first measurement is performed on ultraviolet absorption of Ag₉ ⁺. Temperature dependence of the spectrum is presented by cooling the ion trap down to 10 K.     

Off-axis re-entrant cavity ring-down spectroscopy with a mid-infrared continuous-wave optical parametric oscillator

We demonstrate an off-axis cavity ring-down spectroscopy system, which uses a mid-infrared continuous-wave optical parametric oscillator as a light source. Off-axis injection with re-entrant configuration of the ring-down cavity is used to achieve high spectral resolution while maintaining high measurement speed. This makes the setup suitable for sensitive molecular spectroscopy in the mid-infrared region, particularly for studies that require high temporal resolution. Formaldehyde (H₂CO) absorption spectrum at 3.4 µm is measured using the off-axis re-entrant cavity ring-down spectrometer.     

Near infrared cw-CRDS coupled to laser photolysis: Spectroscopy and kinetics of the HO2 radical

We present in this work a new experimental set-up for sensitive detection of reactive species: continuous wave cavity ring-down spectroscopy (cw-CRDS) as a detection method in laser photolysis reactor. HO₂ radicals were generated by using a 248 nm photolysis of SOCl₂/CH₃OH/O₂ mixtures and were detected in the first vibrational overtone of the OH stretch around 6625 cm^-1, using a DFB diode laser. In order to perform the spectroscopic and kinetic measurements of the HO₂ radical, two different timing schemes have been used. The absorption line strength of the transition at 6625.784 cm^-1 has been extracted from kinetic measurement to (5.2±1.0)×10^-21 cm² molecule^-1cm^-1. The detection limit for the actual set-up is 2×10¹² molecules cm^-3. PACS 42.62.Fi; 82.33.Tb; 82.20.W     

Using a DS-DBR laser for widely tunable near-infrared cavity ring-down spectroscopy

Studies into the suitability of a novel, widely tunable telecom L-band (1,563–1,613 nm) digital supermode distributed Bragg reflector (DS-DBR) laser for cavity ring-down spectroscopy (CRDS) are presented. The spectrometer comprised of a 36.6?cm long linear cavity with ring-down times varying between 19–26 μs across the 50 nm DS-DBR wavelength range due to changes in the cavity mirror reflectivities with wavelength. The potential of such a broadband, high-resolution CRD spectrometer was illustrated by investigating several transitions of CO₂ in air, a 5 % calibrated mixture and breath samples. Allan variance measurements at a single wavelength indicated an optimal minimum detectable absorption coefficient (α _min) of 3 × 10^?10 cm^?1 over 20 s.     

Theoretical detection limit of saturated absorption cavity ring-down spectroscopy (SCAR) and two-photon absorption cavity ring-down spectroscopy

Giusfredi et al. (Phys Rev Lett 104, 110801, 2010), have developed a new approach to cavity ring-down spectroscopy where a saturable sample absorption is determined simultaneously with the cavity loss, providing immunity to changes in cavity loss, thereby allowing for lower analyte detection limit. This paper presents an error analysis that provides predictions of the ultimate sensitivity limits that can be realized with this detection method. In particular, the sensitivity is strongly dependent upon the initial degree of saturation of the sample, and optimal values for this are determined both for photon detector and shot-noise-limited detection of both inhomogeneous and homogeneous broadened spectroscopic lines. Also presented are sensitivity limits expected for two-photon absorption spectroscopy determined by cavity ring-down spectroscopy.