中红外差频光源应用于实际大气水汽浓度测量

基于非线性光学效应,采用差频发生技术(Difference frequency generation)和准相位匹配技术(Quasi-phase matching),在周期性极化的铌酸锂晶体(PPLN)中产生了中红外的可调谐激光源。泵浦光是一个功率为1 W、调谐范围在770到870 nm之间的连续可调谐钛宝石激光器。信号光是一个功率为1 W、单频连续的Nd∶YAG激光器。当晶体的光栅周期为20 μm、温度调谐范围内在室温到200 ℃之间时,能够产生2.8 μm附近的、功率约为1～2 μW的差频光源。基于这个光源,采用直接吸收光谱方法测量了实验室大气中的水汽(001←000)吸收带的吸收光谱。依据大气中水汽分子在8.5 cm的吸收光程条件下的吸收光谱,成功地测量得到了大气中的水汽浓度。     

碘稳频中红外差频激光光谱技术

为实现中红外波段的高精度线型研究,建立了一套在2.5～5um波段连续可调谐的中红外差频激光光谱测量系统.基于宽带连续可调谐钛宝石激光器(700 ～900 nm)和单频连续Nd:YAG激光器(1064 nm),利用碘多普勒展宽吸收和频率调制技术,对Nd:YAG激光的频率进行反馈控制,使1064 nm的Nd:YAG激光的波长稳定性好于1X10-5 cm-1由此差频输出的波长稳定性达到1×10-1cm-1水平,适合高精度的线形研究.并通过对CH4分子在2927 cm-1附近吸收谱线的测量,表明该系统可以结合频率调制方法,进行高灵敏的光谱检测.     

基于光纤激光器的中红外差频多波长激光产生

针对由YDFL和EDFL作为基频光源的QPM-DFG激光系统,利用PPMgLN晶体的色散关系及其温度特性,有效拓宽了QPM波长接受带宽.模拟结果表明,当采用1550和1060 nm波段的EDFL和YDFL分别作为DFG的信号和抽运光源时,对于相同的中红外波段,满足QPM条件所允许的抽运光波长变化范围远大于信号光波长变化范围.当固定信号光波长为1560 nm时,对于给定的晶体温度,1060 nm波段抽运光的QPM接受带宽超过17 nm,对应于中红外差频光带宽可约180 nm.采用多波长YDFL作为抽运源,单关键词：差频产生准相位匹配多波长中红外光纤激光器     

基于被动全光同步的高效率中红外差频产生技术研究

实验探究了基于被动全光同步的中红外差频产生技术,采用主-从注入锁定实现了全保偏掺镱和掺铒锁模光纤激光器的同步脉冲输出,并经过级联光纤放大在PPLN晶体中获得了中心波长为3071 nm的中红外皮秒脉冲,最大泵浦光转换效率为68.3％,峰值平均功率达1.36 W.研究发现,所使用的同步脉冲诱导差频技术能够显著降低中红外产生...     

红外差分光学吸收光谱技术测量环境大气中的水汽

研究了基于红外差分光学吸收光谱技术的环境大气中的水汽测量方法. 所用实验装置由自制的非分散红外多组分气体分析仪改装而成, 根据HITRAN数据库提供的线强参数,采用Voigt展宽线型和方法,并考虑温度、 气压及仪器函数的影响,计算出了水汽反演波段的有效吸收截面. 将反演的水汽浓度与非分散红外分析仪的测量结果进行了实时对比, 得到了较好的测量一致性,测量相关系数为0.93347. 为今后采用红外DOAS技术测量其他在紫外可见波段无吸收或仅有弱吸收的气体 (如CO₂, CH₄, CO, N₂O等)提供了可借鉴的解决方案.     

差频产生中红外飞秒激光脉冲的研究进展

中红外飞秒激光脉冲在科研、民用及军事等方面都有重要的应用,文章回顾了产生中红外飞秒激光脉冲的几种方法,结合差频法产生中红外飞秒脉冲的优点,详细介绍了差频产生中红外飞秒激光脉冲的研究进展,最后进行了总结和展望.     

差频产生中红外飞秒激光脉冲的研究进展

中红外飞秒激光脉冲在科研、民用及军事等方面都有重要的应用,文章回顾了产生中红外飞秒激光脉冲的几种方法,结合差频法产生中红外飞秒脉冲的优点,详细介绍了差频产生中红外飞秒激光脉冲的研究进展,最后进行了总结和展望.     

基于差频中红外激光的痕量气体高分辨光谱检测研究

研究了基于差频光源的高分辨中红外激光光谱检测系统,差频中红外光源使用两台近红外半导体激光器作为种子光源,采用PPLN晶体作为非线性混频器件,结合准相位匹配技术实现了3.2~3.7 μm中红外相干光源输出,最大差频输出功率约为1 μW.以CH₄为例检验了系统的高分辨红外光谱检测特性,选择CH₄分子3 028.751 cm^-1 v₃基频吸收线作为分析谱线,10 cm光程的检测限为0.8 ppm.光谱数据分析表明,系统检测限主要受到标准具光学噪音的限制.     

基于差频中红外激光的痕量气体高分辨光谱检测研究

研究了基于差频光源的高分辨中红外激光光谱检测系统,差频中红外光源使用两台近红外半导体激光器作为种子光源,采用PPLN晶体作为非线性混频器件,结合准相位匹配技术实现了3.2～3.7μm中红外相干光源输出,最大差频输出功率约为1μW.以CH2为例检验了系统的高分辨红外光谱检测特性,选择CH4分子3 028,751 cm-1v3基频吸收线作为分析谱线.10 cm光程的检测限为0.8 ppm.光谱数据分析表明,系统检测限主要受到标准具光学噪音的限制.     

频差偏差对全视场外差测量精度的影响

根据全视场外差测量的相关理论,推导了频差偏差与仪器测量精度的相互关系.分析了频差大小、频差偏差、采集初始时间、初始相位、采样频率和采样周期数等相关参数对测量精度的影响.研究结果可以作为全视场外差测量设备设计、参数选取的理论依据;并给出了通过合理选择采样时间和采样帧数提高测量精度的一种方法.     

A spectroscopic study of water vapor isotopologues H2O, H2O and HDO using a continuous wave DFB quantum cascade laser in the 6.7 μm region for atmospheric applications

A quantum cascade spectrometer was used in the laboratory to study H₂¹⁶O, H₂¹⁸O and HDO line intensities near 6.7 μm. The spectral region ranging from 1483 to 1487 cm⁻¹, which is suitable for the in situ laser sensing of these isotopologues in the atmosphere, was investigated using a continuous-wave distributed feed-back quantum cascade laser. Eight lines of water vapor isopologues were studied—one line of the ν₂ band of H₂¹⁶O, one line of the 2ν₂-ν₂ band of H₂¹⁶O, two lines of the ν₂ band of H₂¹⁸O and four lines of the ν₂ band of HDO were carefully revisited. The measured intensities were thoroughly compared to relevant molecular databases and other experimental and calculated results. We also observe that the H₂O, D₂O, HDO equilibrium constant agrees excellently with previously determined values.     

中红外光谱应用于船用机械油液含水量定量测量的研究

设计了一种新的进样装置,利用傅里叶变换红外光谱仪来获得油液光谱数据。采用在不含水的液压油中混入不同量水的方式制备待测油液样品,采集不同含水量油液在3 780～3 500cm-1波段的光谱并进行积分,得到该波段的吸收能量数据。分析实验数据发现,红外光谱的吸收能量与油液水含量之间满足二次曲线函数关系,拟合得到的二次曲线与实验数据之间的相对误差在0.01%量级。该方法可以作为一种用于定量测量船用机械油液含水量的有效方法,并指导开展相关基于中红外发光二极管和光电二极管能量吸收的传感器的研制。     

基于中红外LED的润滑油水分含量测量研究

针对船舶机械润滑油中水分含量的测量问题,研究了基于中红外LED的油液水分含量测量方法。利用峰值发射波长为2 840 nm,半高宽为400 nm的中红外LED作为发射光源,发射的红外光进入油样,一部分被吸收,剩下的透过油样被红外探测器接收,根据油样对光能的吸光度确定油液中水分含量。实验设计了红外光发射、吸收和探测的装置,采用氟化钙晶片作为窗片,选择截面为圆形的硬质金属线圈作为垫圈以保证精确的油膜厚度,采用探测波长范围为2 500～4 800 nm,响应时间为10～20 ns的光电二极管作为光强探测器。开发了信号的前置放大和基于单片机的数据采集、储存和通讯系统。通过实验,获得了含水质量分数为0,0.062 5%,0.125%,0.25%,0.375%和0.5%六个油样的吸光度数据,利用最小二乘法对数据进行拟合,得到吸光度和含水量的线性回归方程。对误差进行量化分析,回归方程和数据点的决定系数为0.996。最后,为了检验该测量方法的精确性,用含水量为0.317 5%的油样进行验证,利用实验装置测量吸光度,代入回归方程计算含水量, 结果显示通过该方法测得的含水量和实际含水量的相对误差为2.7%,满足工程实际需求,说明该方法能够准确测量油液中的含水量。     

Water line parameters for weak lines in the range 7400-9600 cm

A long pathlength, Fourier transform spectrum of pure water vapour [J. Mol. Spectrosc. 211 (2002) 169] has been fitted and analysed. Line centres, intensities, and self-broadening parameters have been obtained for about 3900 lines with intensities less then 1 × 10⁻²⁴ cm/molecule. Transitions to 240 newly observed energy levels of H₂O have been identified. 855 lines have been assigned to three other major isotopologues of water. It is pointed out that a new intensity measurements are needed for the stronger lines in this region.     

用吸收光谱法测量COIL的水汽含量

 分析了利用吸收光谱法测量氧碘化学激光器的水汽含量的原理,在氯气流量为0.1 mol/s的N₂-COIL上进行了测试实验。实验结果显示,在常规工作条件下,由于BHP温度变化所引起的水汽百分含量变化仅为0.1%,可以忽略;水汽含量随稀释气体流量增大而增加,气体流速是引起水汽含量变化的主要原因,实验中应把氯气和氧气的比例控制在4∶1之内。     

Spectrum of hot water in the 2000-4750 cm frequency range

An emission spectrum recorded in an oxyacetylene torch [P.-F. Coheur, P.F. Bernath, M. Carleer, R. Colin, O.L. Polyansky, N.F. Zobov, S.V. Shirin, R.J. Barber, J. Tennyson, J. Chem. Phys. 122 (2005) 074307] is analyzed for the region covering stretching fundamentals and associated hot bands of water. Many lines could be assigned on the basis of previously determined energy levels. New assignments made with a new variational linelist allow a further 800 energy levels covering 15 vibrational states and rotations up to J = 32 to be assigned. A simultaneous re-analysis of previously reported sunspot absorption spectra leads to the assignment of 581 further lines in the L-band spectrum and 67 in the N-band spectrum.     

Fourier transform absorption spectra of H2O and H2O in the 3ν + δ and 4ν polyad region

Fourier transform absorption spectra of H₂¹⁸O-enriched and H₂¹⁷O-enriched water vapor in the 3ν + δ and 4ν polyad region have been analyzed. With the aid of theoretically calculated linelists, we have assigned 1014 lines attributed to H₂¹⁸O and 836 lines of 855 attributed to H₂¹⁷O. Seven new band origins are found for H₂¹⁷O and one for H₂¹⁸O.     

Collisional parameters of H2O lines: Velocity effects on the line-shape

This paper is devoted to the effects of velocity on the shapes of six R(J) lines of the ν₃ band of water vapor diluted in N₂. The experiments have been made at room temperature for total pressures between 0.1 and 1.2 atm using a tunable infrared laser frequency difference spectrometer. These measurements, which study broad and narrow lines of low and high J values, are first analyzed using the Voigt and the hard collision (HC) model. It is shown that both lead to unsatisfactory results, the Voigt profile being unable to account for the line narrowing whereas the friction (narrowing) parameter deduced using the HC approach has an unphysical dependence on pressure. Furthermore, at elevated pressure where Dicke narrowing and Doppler effects are negligible, deviations between experimental and fitted profiles are still observed, indicating inhomogeneous effects due to the speed dependence of collisional parameters. In order to go further, an approach based on the kinetic impact equation accounting for both the Dicke narrowing and the speed dependence has been applied. It uses velocity-dependent broadening and shifting coefficients calculated with a semi-classical approach and two parameters. The latter, which govern the memory functions of the modulus and orientation of the H₂O velocity are considered as free parameters and determined from experiments. The results show that all profiles, regardless of pressure and of the transition, can be correctly modeled using a single set of memory parameters. This demonstrates the consistency of the approach, which is then used to analyze the different regimes that monitor velocity effects on the line profile.     

Low-uncertainty H2O line intensities for the 930-nm region

We measured room-temperature H₂O spectra of the 3ν polyad within the wave number range 10 603 cm⁻¹ to 10 852 cm⁻¹ using frequency-stabilized cavity ring-down spectroscopy. More than 70 transitions, divisible into two groups based on their relative intensities (strong and weak) were investigated. For the 23 lines comprising the set of strong transitions, the water vapor sample was prepared as a dilute mixture in a steady flow of N₂ carrier gas, and the measurement of the water vapor sample number density was linked to primary methods of humidity generation. For these strong transitions, the measured line intensities were within 1% of previous measurements. The line intensity measurements of the weaker H₂O transitions, were made on samples of static pure water vapor, and these results were systematically greater than previous measurements by approximately 20%.