Population of molecules as strongly anharmonic oscillators in a diatomic gasdynamic laser

Population distribution is studied quantitatively for a diatomic gasdynamic laser in which the molecules behave as strongly anharmonic oscillators under the action of a Morse internuclear potential. In fact, mathematical relationships concerning the two fundamental parameters associated with anharmonicity are derived.     

Diatomic gasdynamic lasing molecules as quantum quasi-harmonic oscillators

We investigate the role played by the molecules as quantum oscillators in a diatomic gasdynamic laser by considering quasi-harmonic behaviour within the context of one-dimensional quantum anharmonic oscillators. Vibrational energy levels depending upon a parameter relative to anharmonicity are discussed in terms of the values taken on by this parameter and the values taken on by the vibrational quantum number.     

Dynamical aspects of two-molecule collision process in a diatomic gasdynamic laser

A dynamical analysis on the basic collision process between two molecules is presented within the context of diatomic gasdynamic lasers. In particular, the kinetic energy of the colliding molecules resulting from the process above is considered for quite highly excited bound states from a quasi-classical point of view. In this analysis, the magnitude of molecule velocity is calculated and discussed in terms of the anharmonicity of a given molecule as a quantum anharmonic oscillator.     

Frequency tunable single-line pulsed first-overtone carbon monoxide laser

Tunable single-line first-overtone (FO) CO lasing on wavelengths from 2.7 up to 4.2 μm corresponding to overtone vibrational transitions from 13→11 up to 38→36 on 413 ro-vibrational lines was experimentally obtained. A parametric study of energetic and spectral characteristics of the single-line FO CO laser was carried out. Energy distribution over ro-vibrational lines was measured. The maximum specific output energy (SOE) came up to 3 J/l Amagat, with single-line output efficiency being up to 0.6%. For the first time, a multi-quantum theoretical model was used to describe the tunable single-line FO CO laser. This multi-quantum approach demonstrated better agreement between theoretical calculations and observed experimental data for laser output as a function of vibrational quantum numbers.     

Evaluation of downstream-mixing scheme for 9.4-µm CO2 gasdynamic laser

A theoretical analysis of a downstream-mixing 16-μm CO₂ gasdynamic laser revealed the possibility of utilizing the downstream-mixing scheme for the generation of 9.4-μm radiation using a CO₂ gasdynamic laser. The flow-field has been analyzed using complete two-dimensional, unsteady laminar form of Navier-Stokes equations coupled with the finite rate vibrational kinetic equations. The analysis showed that integrated small-signal gain of 11.5m⁻¹ for Lorentzian broadening and 4.8m⁻¹ considering Voigt function can be obtained for N₂ reservoir temperature of 2000°K and velocity ratio 1:1 between the CO₂ and N₂ mixing streams. These results (presented in graphs) clearly highlight the large potential of downstream-mixing CO₂ gasdynamic laser for 9.4-μm laser generation.     

固体推进剂燃烧驱动CO_2气动激光小信号增益测量

介绍了固体推进剂燃烧驱动 CO2 气动激光小信号增益测量的原理、方法及实验系统 ,重点说明小信号增益测量光路设计、热敏电阻红外探测器工作原理、增益输出信号滤波和放大电路设计及数据采集系统的硬件配置和软件编制原则 ,给出典型实验测量结果。实验证明 ,采用放大法可较为准确的测量固体推进剂燃烧驱动 CO2 气动激光小信号增益     

固体推进剂燃烧驱动CO2气动激光小信号增益测量

介绍了固体推进剂燃烧驱动CO2气动激光小信号增益测量的原理、方法及实验系统,重点说明小信号增益测量光路设计、热敏电阻红外探测器工作原理、增益输出信号滤波和放大电路设计及数据采集系统的硬件配置和软件编制原则,给出典型实验测量结果。实验证明,采用放大法可较为准确的测量固体推进剂燃烧驱动CO2气动激光小信号增益。     

An optimization analysis on the molecular vibrational energy eigenvalues of a diatomic gasdynamic laser

We study briefly the eigenvalue spectrum corresponding to the vibrational-energy levels of the molecules as anharmonic oscillators in a diatomic gasdynamic laser by calculating the maximum eigenvalue when all the possible diatomic configurations are considered within the context of gasdynamic lasers. In this context, a parameter which characterizes the anharmonicity of a given diatomic molecule as a one-dimensional oscillator is used in our calculations.     

气动激光器喷管非平衡流2维数值仿真

将Anderson的两振型三温度弛豫模型和严海星整理的弛豫数据相结合,采用2维守恒型方程组对按照最小长度喷管型面设计方法设计的、面积比分别为50和20的气动激光器喷管非平衡流场进行了数值仿真。小信号增益计算结果在每个计算点都和J. S. Vamos等人针对这两种喷管的小信号增益测量试验结果符合很好,解决了传统的准1维非平衡流分析方法不能很好地和试验结果相符的问题,对气动激光器喷管性能设计提供了更精确的评估方法。     

固体推进剂燃烧驱动CO2气动激光小信号增益测量

 介绍了固体推进剂燃烧驱动CO₂气动激光小信号增益测量的原理、方法及实验系统,重点说明小信号增益测量光路设计、热敏电阻红外探测器工作原理、增益输出信号滤波和放大电路设计及数据采集系统的硬件配置和软件编制原则,给出典型实验测量结果。实验证明,采用放大法可较为准确的测量固体推进剂燃烧驱动CO₂气动激光小信号增益。     

任意长度喷管型面设计方法在气动激光器喷管设计中的应用

 将一种新的任意长度喷管型面设计（ALN）方法应用于气动激光器喷管型面设计,在相同的喷管出口设计马赫数、喷管喉部高度及喷管扩张段长度条件下,设计了4条ALN方法喷管型面,并和一条最短长度（MLN）喷管型面作对比,采用2维气动激光器增益场仿真方法对5个喷管的小信号增益场进行仿真。计算结果表明:ALN方法可以有效地实现增益场分布的控制,选择合理的设计参数得到的喷管长度比MLN喷管更短,小信号增益更大。     

任意长度喷管型面设计方法在气动激光器喷管设计中的应用

将一种新的任意长度喷管型面设计（ALN）方法应用于气动激光器喷管型面设计,在相同的喷管出口设计马赫数、喷管喉部高度及喷管扩张段长度条件下,设计了4条ALN方法喷管型面,并和一条最短长度（MLN）喷管型面作对比,采用2维气动激光器增益场仿真方法对5个喷管的小信号增益场进行仿真。计算结果表明:ALN方法可以有效地实现增益场分布的控制,选择合理的设计参数得到的喷管长度比MLN喷管更短,小信号增益更大。     

红外场对双原子分子振动布居影响的李代数方法研究

采用李代数方法研究双原子分子在红外场中的振动跃迁,给出了体系跃迁概率的解析表达,并讨论了红外场的频率、光强和脉冲持续时间分别对NaCl和LiH分子振动基态和第一振动激发态上粒子数布居的影响. 关键词： 李代数方法 红外场 振动布居 双原子分子     

Resonant raman in impurity molecules: an exact solution in the presence of harmonic and anharmonic vibrational potential

Summary Resonant Raman response of impurity molecules in nonmetallic solid matrix is solved exactly. The model embodies the nonradiative interaction between impurity molecule and the nearest-neighbour molecules in the solid. The interatomic vibration of the excited electronic level of the molecule is modelled by harmonic and anharmonic potential. Frank-Condon and anharmonic effects are discussed by selected numerical examples.

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Riassunto Il tensore Raman risonante di molecole di impurezza in solidi molecolari è calcolato esattamente. Il modello di hamiltoniana proposto contiene la diseccitazione non radiativa della molecola di impurezza mediante l'interazione con la matrice solida ed inoltre le vibrazioni interatomiche della molecola sono rappresentate da un potenziale armonico o anarmonico. L'effetto Frank-Condon ed il potenziale anarmonico delle vibrazioni della molecola sono risolti esattamente per la prima volta e discussi mediante esempi numerici.

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Резюме Определятся реазонансный Раманоский отклик от молекул примеси в неметаллической твердой матрице. Предложенная модель включает нерадиационное взаимодействие между молекулой примеси и ближайшими молекулами твердого тела. Межатомное колебание возбужденного злектронного уровня молекулы моделируется с помощью гармонического и ангармонического потенциала. На численных примерах обсуждвются зффект Франка-Кондона и ангармонические зффекты.

     

钛宝石飞秒激光器中孤子分子的内部动态探测

孤子是自然界中一种基本的非线性波动传递形式,孤子间的相互作用能够映射出复杂非线性系统的多体动力学过程,具有重要的基础研究价值.被动锁模激光器是研究孤子相互作用的理想平台.光孤子之间的吸引、排斥作用能够形成孤子分子,而时间拉伸色散傅里叶变换(TS-DFT)技术使得实时探测孤子分子动力学成为可能.基于TS-DFT技术,本文实验研究了钛宝石飞秒激光器产生的孤子分子的内部动态,通过改变抽运功率,分别观察到了间隔为180 fs的稳定的孤子分子和间隔为105 fs的具有微弱相位振荡的孤子分子,后者的振动幅度仅为0.05 rad.实验发现受到环境影响,稳定态的孤子分子还能够转变为相位滑动状态.这些间隔为百飞秒量级的光学孤子分子对于研究孤子的近程非线性相互作用具有突出的意义.     

Femtosecond laser ionization and fragmentation of molecules for environmental sensing

Recent studies have demonstrated that femtosecond laser pulses have high potential in application to environmental science. Because of the properties of ultrafast, broadband and high power, the propagation of femtosecond laser pulses in air can lead to the generation of a strong field of 10¹³–10¹⁴ W/cm² with a large distance range from meter to kilometers. The strong laser field induces ionization and fragmentation of molecules in the laser propagation path, resulting in characteristic fingerprint emissions. This paper mainly focuses on recent research advances in environmental sensing by using femtosecond laser pulses through strong‐field‐induced ionization and fragmentation of molecules. The fingerprint emissions of molecules in strong laser fields are discussed based on the understanding of strong‐field–molecule interactions in atmospheric as well as in vacuum environments. This is followed by a comprehensive review of several recently developed optical methods for coherent control of fingerprint emissions of molecules. Lastly, both current challenges and a future perspective of this dynamic field are discussed.

     

Influence of laser fields on the vibrational population of molecules and its wave-packet dynamical investigation

The time-dependent wave packet method is used to investigate the influence of laser-fields on the vibrational population of molecules.For a two-state system in laser fields,the populations on different vibrational levels of the upper and lower electronic states are given by wavefunctions obtained by solving the Schro¨dinger equation with the splitoperator method.The calculation shows that the field parameters,such as intensity,wavelength,duration,and delay time etc.can have different influences on the vibrational population.By varying the laser parameters appropriately one can control the evolution of wave packet and so the vibrational population in each state,which will benefit the light manipulation of atomic and molecular processes.     

Wideband CO laser in problems of laser sensing of minor gaseous components in the atmosphere

In the present work it is demonstrated that a wideband CO laser operating at fundamental and overtone vibrational transitions is a promising source of laser radiation for remote laser sensing of the atmosphere. A compact slab RF-discharge CO laser has been designed. The optimal operating conditions are determined for this CO laser. In experiments, the maximum average output laser power was ∼12 W for lasing efficiency of ∼14%. Under fixed experimental conditions, stable lasing (with fluctuations of the output laser characteristics ≤5%) was observed during more than one hour, which suggests that we first excited the sealed-off mode of cryogenic slab RF-discharge CO laser. The frequency-selective mode was first obtained for this laser. Wavelengths for sensing of nitrous oxide, nitrogen dioxide, methane, formaldehyde, and some other gases on near-ground propagation paths are determined. Our experiments and calculations confirm that this CO laser is promising for laser gas analysis. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 76–83, November, 2008.     

孤子分子/类噪声脉冲可切换的混合锁模光纤激光器

不同类型脉冲之间的演化是被动锁模光纤激光器丰富动力学的体现。报道了一种可实现多种脉冲切换的混合锁模光纤激光器,当泵浦功率为400 mW时实现了孤子分子、谐波锁模、孤子簇之间的相互切换。增加泵浦功率至600 mW时获得了类噪声脉冲输出,对应的输出功率和单脉冲能量分别为15.2 mW和0.86 nJ。通过调节偏振控制器实现了类噪声脉冲中心波长从1 895 nm到1 930 nm可调谐。所搭建的激光器具有锁模脉冲可切换,波长可调谐,能自启动等优点。     

Kinetic energy release of diatomic and linear triatomic molecules in intense femtosecond laser fields

The kinetic energy release of fragment ions produced by the interaction of femtosecond laser pulse radiation with diatomic and linear triatomic molecules N_2, CO, CO_2 and CS_2 is investigated. In the case of linear polarization, angles at which the kinetic energy release of ions has the maximum value are different from the alignment of molecules though the kinetic energy release of fragment atomic ions depends on the angle between the laser polarization vector and the detection axis of the time-of-flight. For the diatomic molecules, the critical internuclear distance in multielectron dissociative ionization with a circularly polarized light is larger than that with a linearly polarized light. For linear triatomic molecules, our data indicate that a concerted Coulomb explosion process is a universal phenomenon in the interaction of molecules with intense laser fields, even in the circularly polarized regime. During two C－O (or C－S) bonds breaking simultaneously, the C ion obtained larger energy in circular polarization than that in the linear polarization. Different variations of kinetic energy release between the diatomic and the linear triatomic molecules are discussed.