高振动激发态KH(X1Σ+, V=14-21)与CO2碰撞中的振动-转动能量转移

利用泵浦-探测技术研究高振动激发态KH(V=14-21)分子与CO2的振动-转动碰撞转移过程。脉冲激光激发KH分子至高位振动态，与CO2发生振动-转动能量转移，使CO2高位转动态得到布居，通过测量CO2(0000，J)转动态分布，得到其平均转动能和平均转动能变化，发现振动量子数V从14增加至21时，CO2平均转动能变化增加了2.33倍；测量CO2转动能级的多普勒增宽吸收线，得到V=14和20时，其获得的平均平动能大体随J增大而线性增大；最后，在单一碰撞条件下，测量KH(V=14-21)与CO2(0000，J)的振动-转动碰撞能量转移速率系数，结果显示V=19的总碰撞速率系数是V=14的4.5倍，而V>19则呈下降趋势。     

A theoretical study of the atmospheric pulsed H2+ F2chemical laser including rotational nonequilibrium effects

An atmospheric pulsed F2/H2/He chemical laser is studied numerically by a model which incorporates rotational nonequilibrium effects. The results are compared with experimental results of Chen et al. The fit between the experimental and theoretical results was found to be reasonably good. The results were also compared with those obtained from a model with an equilibrated rotational distribution. It is found that inclusion of a rotational nonequilibrated distribution which decreases the output energy by 25 percent has a certain effect on the output energy distribution among the various vibrational states but is of little importance for the lasing duration.     

Performance and Spectral Tuning of Optically Overtone Pumped Molecular Lasers

A laser model was developed to predict the performance of optically pumped higher overtone molecular lasers under pulsed and continuous wave (CW) excitations. This model takes into account up to 30 rotational levels in each of the eight vibrational states considered. Collision-induced relaxation among rotational levels, vibrational levels, energy transfer to translational degrees of freedom, and interactions with buffer gas, and the temperature dependence of these processes are included. Using parameters for a second overtone pulse pumped HBr laser, a complete lasing cascade can be expected at a certain pump pulse fluence resulting in maximum achievable efficiencies approaching 80%. Optimum operational pressure and temperature conditions are determined by the gas kinetic rates and line broadening effects. Frequency tuning and spectral narrowing of the laser output is possible with the insertion of intracavity filters without sacrificing laser output power owing to efficient energy redistribution between rotational levels mediated by appropriate buffer gases. CW lasing using waveguide (WG) like geometries is possible with efficiencies approaching 92% for first overtone pumped lasers. Heat conduction through the active gas enhanced by buffer gases and subsequent heat dissipation through the cooled WG walls are expected to handle the thermal load up to kW output power levels.     

Experiment on cross relaxation in CO2

The details of the hole-burning process are studied experimentally and theoretically in a Doppler-broadened gain or absorption line in pure CO2and in CO2-N2mixtures contained in a test cell. The change of absorption or gain of the test cell when irradiated by a saturating laser in aPtransition is probed with another laser operating in one of manyRtransitions. In this way one may determine the rate of velocity cross relaxation within a single rotational-vibrational level and the rate of cross relaxation between different rotational levels of the upper and lower vibrational states. When the probing laser shares a common upper or lower level with the saturating laser, a pip is observed in the differential absorption or gain profile at total pressures of less than 0.5 torr. At higher pressures the relaxation across the velocity profile eliminates the pip. An analysis is presented of the population distribution in the multilevel system of CO2. Three of the relaxation rates (describing the relaxation across the velocity profile of a single level, the relaxation among rotational levels of the vibrational state, and the phenomenological relaxation rate of entry into and departure from the upper and lower vibrational states) are determined. The last of the three rates is found to be dominated by diffusion at the pressures used in the experiment.     

Rb(5PJ)+(Ne、N2)碰撞能量转移

在气体样品池条件下,研究了Rb(5PJ) (Ne、N2)碰撞能量转移过程.对于5PJ与Ne的碰撞,电子态能量仅能转移为Ne原子的平动能.在与N2的碰撞中,向分子振转态的转移是重要的.调频半导体激光器稍微调离共振线,激发Rb原子至Rb(5P3/2)态,在不同的Ne或N2气压下,测量了5P1/2→5S1/2与5P3/2→5S1/2荧光强度比.利用速率方程分析,可以得到碰撞转移速率系数,对于Ne,5P3/2→5P1/2转移速率系数为1.53×10-12cm3s-1.对于N2,由5PJ Ne和5PJ N2二种情况下5P1/2与5P3/2荧光的相对强度比,利用最小二乘法确定5P3/2→5P1/2.转移速率系数为8.83×1011cm3s-1,5PJ态猝灭速率系数为1.25×10-10cm3s-1.对实验结果进行了定性的讨论.     

The water-vapor laser

Water-vapor lasers oscillate on more than a hundred pulsed lines and over a dozen CW lines over the wavelength range from 7 to 220 μ (1300-45 cm^-1). Nearly eighty of these lines are now identified as vibrational-rotational and pure rotational transition in the low-lying vibrational states of the water-vapor molecule. The structure of the water-vapor molecule is reviewed, and the mechanisms responsible for creating population inversions in water-vapor discharges are discussed. It is shown how a model, based on perturbations between rotational levels of different vibrational states, can be used to explain the laser action and to predict new laser lines. Detailed summaries of data on all observed laser lines in H2O¹⁶, H2O¹⁸, and D2O¹⁶and their identifications are presented. Some of the lines are newly reported, and more accurate wavelength measurements have been made for many of the lines. The observation of predicted laser lines in H2O¹⁸is shown to be a strong confirmation of the perturbation model. The list of references contains a fairly complete bibliography of previous work on the water-vapor laser, and a representative bibliography of work on the energy-level structure of the water-vapor molecule.     

Computer model of the electron-beam excited XeF(B-X) laser

The authors report results on the computer simulation of electron-beam pumped XeF lasers user common conditions, as well as under elevated temperature and high pumping rates that are known to improve laser performance. The Boltzmann equation for the electron energy distribution function and the chemical kinetics equations were solved in a consistent manner. The model took into account five vibrational levels of the electronic B state and seven levels for the C and X states of the XeF molecule. The model used gives reasonable agreement with the results of small signal gain measurements. A method of taking into account the finite rate of rotational relaxation makes it possible to obtain time dependencies of the lasing power in different spectral bands that qualitatively agree with those measured in experiments at different temperatures and pump rates     

Assignment of laser lines in an optically pumped submillimeter and near millimeter laser: (H2CO)3

A large number of emissions is obtained in the submillimeter and near millimeter range with the (H₂CO)₃ laser optically pumped by a CO₂ laser. A study of the microwave absorption spectrum of the molecule carried out simultaneously with the submm analysis allows us to assign six of the laser lines in thev ₅ excited state of the molecule and to determine the rotational constants and vibrational energy ofv ₅.     

Far-infrared laser gain resulting from rotational perturbations

A simplified model is used to calculate the unsaturated gains of far-infrared rotational and vibrational-rotational laser transitions that are caused by rotational perturbations. Inversions are derived from the perturbation of an initial Boltzmann distribution of rotational populations, permitting the calculation of laser gains in terms of the perturbation parameters and the vibrational populations. The gain equations are applied to the three perturbations of H2O¹⁶that result in the largest number of laser lines. Numerical gain values in good qualitative agreement with experimental results are obtained.     

Dependence of rotational and vibrational Raman scattering onfocusing geometry

Stimulated rotational and vibrational Raman scattering in H₂ was investigated with a circularly and a linearly polarized XeCl laser beam and the influence of the focusing geometry on the threshold for rotational and vibrational scattering, respectively, was studied. It is shown that with a circularly polarized pump beam a high-angle focusing geometry allows to get only rotational Raman scattering, whereas a low-angle focusing geometry provides only vibrational Raman scattering for gain suppression effects     

利用CARS研究Li2（A^1∑u^＋）-H2碰撞中电子一振转能量转移

利用相干反斯托克斯拉曼谱（CArtS）分析了H2与Li2（A^1∑u^＋）-H2碰撞的振转态布居分布。扫描cARS谱表明了在能量转移过程中H2的v=1,2,3振转能级上得到布居,由CARS峰值得到两个可能的布居数比值,通过解速率方程组并通过时间分辨CARS轮廓模拟,确定了实际的布居数之比。得到了H2在V=1,2,3能级...     

Far-infrared raman laser with high intensity laser pumping

Theoretical and experimental results are presented for a pulsed far-infrared (FIR) molecular gas laser with high intensity laser pumping. In these FIR lasers, high intensity pumping is found to produce stimulated Raman emission at very large offsets (up to 30 GHz) from resonance with the intermediate state. A theoretical, density matrix model is developed for these lasers to account for simultaneous Raman emission on rotational levels in the ground and excited vibrational states (double Raman resonance). This theoretical approach is necessary in the case of off-resonant, high intensity pumping. Theory predicts the FIR emission frequency, the FIR laser gain, and the pump threshold intensity as a function of pump laser frequency. Experimental results are obtained onP-,Q-, andR-branch transitions in¹²CH3F and¹³CH3F using a single-mode, grating tuned CO2TEA pump laser with an intensity of up to 40 MW/cm². Good agreement is obtained between theory and experiment for the observed values of FIR emission frequency and pump threshold intensity. These results indicate that a widely tunable (150-1200 mum), pulsed FIR CH3F laser could be constructed with a tunable, multiatmospheric CO2pump laser of modest power (about 2-5 MW).     

A time-resolved study of rotational and vibrational excitation and relaxation in the13CH3F optically pumped far-infrared laser

The rotational and vibrational energy transfer processes of the¹³CH3F optically pumped far-infrared (OPFIR) laser have been studied in a time-resolved experiment. The experiment uses a tunable millimeter and submillimeter spectroscopic technique as a diagnostic probe. Included are observations of the fastDelta Jprocesses that closely connect otherJstates withinK = 3to the directly pumpedJ = 5level, a vibrational swapping mechanism that transfers excitation fromK = 3to otherKstates, vibrational relaxation due to both wall collisions and molecule-molecule collisions, the nonunity probability of vibrational deactivation in a wall collision, and pump saturation and hole burning effects due to the CO2pump laser. All of these observations are accounted for in the context of a numerical simulation. This results in a complete map of all of the collision-induced rotation-vibration transitions of importance to this basic OPFIR system including quantitative cross sections for the relevant processes.     

CO_2-N_2-H_2O激光体系的振动弛豫过程

讨论了驰豫过程中的一些重要问题:CO_2(v_3)的分子内V-V传能机制;水对驰豫过程的重要效应的机制;CO_2的v_1与v_2间的共振传能;膨胀流与压缩流的弛豫速率的同异;不同转动能级间和同一振型的不同振动能级间存在不平衡的可能性.指出了需进一步研究的问题.此讨论的内容亦适用于其它气体激光体系.     

Observation of a large number of new laser lines from12CD3F gas optically pumped with a continuouslytunable high-pressure pulsed CO2 laser

An observation is reported of a large number of new laser lines from ¹²CD₃F gas optically pumped with a continuously tunable high-pressure pulsed CO₂ laser. Making use of the coincidence of the 10 μm P and R branches of CO₂ with the v₃ and v₆ vibrational-rotational absorption bands of ¹²CD₃F, 180 laser lines were found in the wavenumber range between 8 and 55 cm^-1, all of them yet unknown; these lines are studied for characteristic properties of laser action. All laser lines are assigned as pure rotational transitions in the vibrational excited or ground states     

Small signal gain in the CO-air-He laser

The small-signal single-pass gain for 24 individual CO laser lines has been measured for a flowing CO-air-He laser. The vibrational-rotationalP(J)_{upsilon,upsilon'}lines considered were for rotational transitions fromJ = 10to 16 and upper vibrational levels fromupsilon = 7to 11. The maximum gain was observed for theP(15)_{10,9}laser line, with an average logarithmic energy gain of2.633 times 10^{-3}cm^-1.     

铯分子亚稳电子态中高位振动态的产生和弛豫

研究了Cs2[13Πu(v)]和Cs原子间的振动能量转移.利用激光感生荧光(LIF)探测Cs2[13Πu(v)]的弛豫过程,由时间分辨LIF的对数描绘得到振动态的有效寿命,从不同Cs原子密度下的有效寿命利用Stern-Volmer公式得到振动能级的弛豫率,速率系数随v的增加而增大.从相邻二振动能级的布居密度之比得到振动...     

New cascade laser transitions in CH2F2 pumped with the 9R32 line of a cw CO2 laser

New cascade laser transitions of¹²CH₂F₂ at 172.50μm, 208.83μm, 220.44μm, 223.99μm and 250.61μm are reported. A waveguide FIR laser was pumped with a quasi cw¹²C¹⁶O₂ laser operating on the 9R32 line. Together with the already known lines at 184.3μm, 196.1μm and 235.9μm, the laser lines can be assigned to rotational transitions in the ν₉ vibrational band of¹²CH₂F₂ and to refill transitions of the vibrational ground state ν₀.     

Multiphoton excitation processes between vibrational states of molecules

An approximation method has been developed to evaluate the perturbation theory expressions for the probabilities of two- and three-photon transitions among vibrational-rotational levels of diatomic and polyatomic molecules. The sum over intermediate rotational states and the degenerate quantum numberMis evaluated for a general case, and the sum over intermediate vibrational states for particular cases. The molecule is taken to be a rotating anharmonic oscillator. The electrical anharmonicity and the effects of the electronic states of the molecule are considered. Two- and three-photon processes, with or without the presence of near-resonant intermediate states, should be observable with available infrared lasers. However, the intensities predicted for the observation of three-photon excitation would result in more dominant effects such as dissociation or gas breakdown.