Calculation of laser induced collisional energy transfer in the Sr-Ca system

Based on the four-state model of laser-induced collisional energy transfer,the cross section of the collisional energy transfer in the Sr-Ca system is obtained.Various factors,including field intensity,relative speed,and temperature,which influence the collisional cross section,are discussed for illustrating the features of the Sr-Ca laser-induced collisional energy transfer(LICET) process.The calculated results show that the LICET spectral profiles obviously become narrower when the laser field intensity i...     

Laser-induced quadrupole-quadrupole collisional energy transfer in Xe-Kr

By considering the relative velocity distribution function and multipole expansion interaction Hamiltonian, a three-state model for calculating the cross section of laser-induced quadrupole-quadrupole collisional energy transfer is presented. Calculated results in Xe-Kr system show that in the present system, the laser-induced collision process occurs for ～4 ps, which is much shorter than the dipole-dipole laser-induced collisional energy transfer (LICET) process. The spectrum of laser-induced quadrupole-quadrupole collisional energy transfer in Xe-Kr system has wider tunable range in an order of magnitude than the dipole-dipole LICET spectra. The peak cross section decreases and moves to the quasi-static wing with increasing temperature and the full width at half peak of the profile becomes larger as the system temperature increases.     

Four-level model of ion-ion laser-induced collisional energy transfer and numerical calculations for Ca~+-Sr~+ system

The four-level model of laser-induced collisional energy transfer(LICET) for the ion-ion collision system is established based on the time-dependent Schro¨dinger equation for the electron dynamics,through which the equations of motion of the probability amplitudes and cross section of the collision system are obtained.Numerical calculations are performed for the Ca+-Sr+ system,with the results showing that the peak of the LICET spectrum appears at a resonant frequency of the transfer laser.The magnitude of the obtained collision cross section is in the order of 10 16 cm2,and is comparable to that obtained in atomic systems,which indicates the validity of the established four-level model.     

Laser induced collisional energy transfer in Sr—Li system

A four-state model considering the relative velocity distribution function for calculating the cross section of laserinduced collisional energy transfer in a Sr-Li system is presented and profiles of laser-induced collision cross section are obtained.The resulting spectra obtained from different intermediate states are strongly asymmetrical in an opposite asymmetry.Both of the two intermediate states have contributions to the final state,and none of the intermediate states should be neglected.The peak of the laser-induced collisional energy transfer(LICET) profile shifts toward the red and the FWHM becomes narrower obviously with laser field intensity increasing.A cross section of 1.2 × 10-12 cm 2 at a laser field intensity of 2.17 × 10 7 V/m is obtained,which indicates that this collision process can be an effective way to transfer energy selectively from a storage state to a target state.The existence of saturation for cross section with the increase of the laser intensity shows that the high-intensity redistribution of transition probabilities is an important feature of this process,which is not accounted for in a two-state treatment.     

Ba-Sr系统激光感生碰撞能量转移的数值计算

以现有的激光感生碰撞能量转移的四能级理论模型为基础,通过直接积分态振幅的运动方程,对弱场、强场两种情况下Ba-Sr系统的激光感生碰撞能量转移过程进行了数值计算,得到了两种情况下的激光感生碰撞跃迁概率和碰撞截面的谱线线型.在弱场情况下的数值计算结果与近似解析解的计算结果符合很好.对强场情况下的数值积分计算结果表明：激光感生碰撞作用随转换激光强度的增大而增强;强场时激光感生碰撞截面谱线的峰值位置明显偏离了共振频率并向紫端移动,且碰撞截面谱线的半宽度(即调谐范围)较之弱场明显变小. 关键词： 激光感生碰撞能量转移 碰撞截面 Ba-Sr系统 强场     

激光感生碰撞能量转移的四能级理论模型

首次考虑了两个中间态对激光感生碰撞能量转移的影响，发展了激光感生碰撞能量转移的四能级理论模型，推导出态振幅的运动方程，并给出碰撞截面的近似表达式，通过对Ｅｕ－Ｓｒ和Ｃｓ－Ｓｒ系统的数值计算表明，当频率差│ω２１│大小和│ω４３│可以相比时，利用三能级近似理论就难以获得令人满意的计算结果，而四能级理论模型则适合于任何情况下的激光感生碰能量转移。     

激光感生碰撞能量转移实验

首次观察到Eu(6s6p)^P9/2至Sr(5s10s)^1So、准稳态翼为紫翼的激光感生碰撞能量转移实验现象,其荧光波长为458.42nm,峰值转移激光波长为459.75nm,并对其激发函数谱随温度和随转移激光能量改变进行实验研究,测量了激光感生碰撞能量转移谱的截面,证实了激光感生碰撞能量转移谱为非对称谱。     

激光诱导下Yb—Ba间的能量转移过程

本文研究了在激光诱导下Ba和Yb的两对非偶极允许能级间的碰撞能量转移,得到了转移截面与诱导激光波长的关系。观察到自旋相互作用对它的影响。 关键词：     

弱场中Ba-Sr系统激光感生碰撞过程的理论研究

针对四能级理论模型的第二种极限情况 ,提出了 Ba- Sr激光感生碰撞能量转移系统 ,该系统满足 |ω2 1| |ω4 3|。利用四能级理论模型对该 Ba- Sr系统进行了数值计算 ,并与三能级近似理论模型的计算结果进行了比较。通过比较四能级理论与三能级近似理论模型的计算结果 ,进一步证实了当 |ω2 1| |ω4 3|时 ,四能级理论模型可以过渡为三能级理论模型     

Xe-Kr laser induced collisional ionization system and experimental preparation of its initial state: Four-photon resonant excitation

This paper proposes a novel one-colour Xe-Kr laser induced collisional ionization system. Considering the level scheme of the system, it finds that the initial state of the reaction--the four 4f levels with even J of Xe-can be prepared through method of four-photon resonant excitation by dye laser with wavelength of -440 nm. Absorption of an additional photon （the transfer laser） of the same wavelength will complete the laser induced collisional ionization process. The resonance enhanced ionization spectrum of Xe by four laser photons at -440nm is measured through time-of-flight mass spectrometry, this aims at the preparation of the initial state of the system proposed. The Stark broadening of the measured spectrum is observed and consistent with the previous study. Analysis of the measured resonance ionization spectrum implies the feasibility of -440 nm four-photon resonant excitation of the initial 4f state of the Xe Kr system proposed in this paper, which prepares for a further experiment of laser induced collisional ionization.     

原子和离子间激光感生碰撞电荷交换的微扰理论

将激光感生碰撞电荷看作一个四体系统，发展了激光感生碰撞电荷电荷的微扰理论，以独立原子和离子的复合态波函数作为激光感生碰撞体系的基组函数，得到了体系态振幅的运动方程。利用激光感生碰撞电荷交换的微扰理论，对Ｃａ＾＋－Ｓｒ间激光感生碰撞电荷交换进行了数值计算，并与Ｇｒｅｅｎ等人的实验结果进行了比较。     

Numerical study of laser-induced collision process in Eu-Sr in strong field

Theoretically based on the four-level model, one LICET process in Eu-Sr system in both weak and strong fields was calculated by immediate numerical integrations. Numerical results in weak field are in fair to good agreement with analytical ones. Numerical results in strong field show that: (a) the peak of the LICET profiles moves to the violet side and the tuning range of the profiles obviously becomes narrower when the laser field intensity increases; and (b) numerical results in strong field differ a lot from analytical ones, which indicates that in strong field, the analytical expressions are not applicable any longer.     

The cross sections and their temperature dependence of collisional energy transfer from high vibrationally excited ethylene molecules to electronic ground state Rubidium atoms

The cross sections and their temperature dependence of collisional energy transfer from the high vibrationally excited C_2H_4 to the electronic ground sate of Rb (V-E) have been studied by the method of IR laser pump combined with fluorescence probe. The fluorescence of rudidium atoms due to V-E energy transfer was detected. The measured rate constants of this V-E energy transfer is about 10~(-10)cm~2molec~(-1)s~(-1) and the corresponding cross section varies from 60 (?)~2 to 90 (?)~2. The cross sections decrease with increasing temperature over the temperature range of 393-683 K.     

高激发态钠原子与分子碰撞能量转移及分子扩散带辐射的增强效应研究

在钠原子分子混合体系中 ,实验研究了加入缓冲气体对高位态原子分子碰撞能量转移和分子扩散带辐射的增强效应 ;运用瞬态碰撞模型作了理论计算 ,理论结果与实验结果相符合     

Laser time-resolved spectroscopy studies of host-sensitized energy transfer in Bi4Ge3O12 : Er3+ crystals

Laser-excited, time-resolved spectroscopy techniques were used to investigate host-sensitized energy transfer in bismuth germanate crystals doped with erbium. The transfer characteristics at room temperature are consistent with a thermally-activated migration process. The transfer rate decreases exponentially as temperature is lowered and reaches a minimum near 75 K. An increase in the transfer rate is observed as temperature is lowered further and the transfer characteristics become consistent with a single step dipole-dipole interaction process. This low temperature behavior is correlated with the observations in undoped bismuth germanate at these temperatures of a significant shift to lower energy of the fluorescence peak position and a significant increase in the fluorescence lifetime. A trapped exciton model is proposed to explain these results.     

Some Observations about the MOLSCAT

For calculation of cross sections for collisional transitions between rotational levels in a molecule, a computer code, MOLSCAT is available. For the transitions between rotational levels in H₂CS due to collisions with He atom, we have calculated cross sections under the CS approximation, for example, for total energy 11 cm^-1. The calculations have been done for the single energy 11 cm^-1 and for ten combinations. We have found that the cross sections for the single energy 11 cm^-1, differ from those in the first seven combinations, but are in agreement with those in the last three combinations. The reason for the difference in the results appears that the MOLSCAT uses the intermediate data of calculations for one energy, in the calculations for other energies. The agreement with the last three combinations may be understood that when the energy of combination is in the decreasing trend, the cross sections for the first (common) energy are equal. It may be suggested to run the MOLSCAT for a single energy at a time.     

High Energy Proton-Proton Elastic Scattering in the Pomeron Exchange Model

We study high energy proton-proton elastic scattering in the framework of Pomeron exchange model. The cross section of the process are calculated without any free parameters. Our finding is that Pomeron exchange theory gives perfect fits to total cross section at the energy of√s higher than 10 GeV and to differential cross section at the momentum transfer [t] less than 1.5 GeV2. For total cross section at lower energy √s ＜ 10 GeV and differential cross section at larger momentum transfer region of |t| ＞ 1.5 GeV2, the Pomeron exchange theory needs to be improved.     

High Energy Proton-Proton Elastic Scattering in the Pomeron Exchange Model

We study high energy proton-proton elastic scattering in the framework of Pomeron exchange model. The cross section of the process are calculated without any free parameters. Our finding is that Pomeron exchange theory gives perfect fits to total cross section at the energy of √(s) higher than 10 GeV and to differential cross section at the momentum transfer |t| less than 1.5 GeV². For total cross section at lower energy √(s)<10 GeV and differential cross section at larger momentum transfer region of |t|>1.5 GeV², the Pomeron exchange theory needs to be improved.     

Numerical analysis of quantitative measurement of hydroxyl radical concentration using laser-induced fluorescence in flame

The aim of the present work is to quantitatively measure the hydroxyl radical concentration by using LIF(laserinduced fluorescence) in flame.The detailed physical models of spectral absorption lineshape broadening,collisional transition and quenching at elevated pressure are built.The fine energy level structure of the OH molecule is illustrated to understand the process with laser-induced fluorescence emission and others in the case without radiation,which include collisional quenching,rotational energy transfer(RET),and vibrational energy transfer(VET).Based on these,some numerical results are achieved by simulations in order to evaluate the fluorescence yield at elevated pressure.These results are useful for understanding the real physical processes in OH-LIF technique and finding a way to calibrate the signal for quantitative measurement of OH concentration in a practical combustor.     

Doubly charged clusters - neutral atom charge transfer: the role of the Coulombic repulsion

We have studied experimentally the collisional charge transfer between a neutral atom and a multicharged metal-atom cluster. The charge transfer cross section measured for Na ₃₁ ^{+ +} + Cs is in the range of 400 ?². The time-of-flight mass analysis of the singly charged collision products demonstrates that an energy of about 0.5 eV is deposited in the cluster fragment during the charge transfer collision. This effect can be interpreted as a charge transfer to an excited state of the metal cluster. The measured cross section for Na ₃₁ ^{+ +} + Cs is larger than the one for Na ₃₁ ⁺ + Cs collisions. This difference between these two systems is due to the existence, for the first one, of a Coulombic repulsion term in the collision output channel. Received 24 October 2000