A practical CuBr laser with flowing buffer gas

Experiments on the lifetime of a CuBr laser with flowing neon as a buffer gas are reported. The CuBr laser with a discharge tube of inner diameter 18 mm, electrode separation 465 mm at an average output power of 3 W, an efficiency of 0.4% for a lifetime of 734 h is obtained. In consideration of the flow of the buffer gas and combined structure of the discharge tube we have achieved prolongation of the laser lifetime.     

Air as a buffer gas in metal-vapor lasers

The output power of two metal-vapor lasers is measured as functions of different buffer gasses. A copper-vapor laser and a gold-vapor laser can be constructed using air as a buffer gas. The output power and stability of the lasers were compared when either He or Ne or air were used as a buffer gas. The results obtained show that the output powers of the lasers are relatively high and have fairly good stability when air was used as buffer gas. Elimination of gas handling and decrease in the volume and weight of the laser system are the greatest advantages of the lasers elaborated.     

The energy distribution of an ion in a radiofrequency trap interacting with a nonuniform neutral buffer gas

An ion in a radiofrequency (rf) trap sympathetically cooled by a simultaneously trapped neutral buffer gas exhibits deviations from thermal statistics caused by collision-induced coupling of the rf field to the ion motion. For a uniform density distribution of the buffer gas, the energy distribution of the ion can be described by Tsallis statistics. Moreover, runaway heating of the ion occurs if the buffer gas particles are sufficiently heavy relative to the ion. In typical experiments, however, ultracold buffer gases are confined in traps resulting in localised, non-uniform density distributions. Using a superstatistical approach, we develop an analytical model for an ion interacting with a localised buffer gas. We demonstrate theoretically that limiting collisions to the centre of the ion trap enables cooling at far greater mass ratios than achievable using a uniform buffer gas, but that an upper limit to the usable mass ratio exists even in this case. Furthermore, we analytically derive the functional form of the energy distribution for an ion interacting with a buffer gas held in a harmonic potential. The analytical distribution obtained is found to be in excellent agreement with the results of numerical simulations.     

A moving interface method for dynamic kinetic–fluid coupling

This paper is a continuation of earlier work [P. Degond, S. Jin, L. Mieussens, A smooth transition between kinetic and hydrodynamic equations, Journal of Computational Physics 209 (2005) 665–694] in which we presented an automatic domain decomposition method for the solution of gas dynamics problems which require a localized resolution of the kinetic scale. The basic idea is to couple the macroscopic hydrodynamics model and the microscopic kinetic model through a buffer zone in which both equations are solved. Discontinuities or sharp gradients of the solution are responsible for locally strong departures to local equilibrium which require the resolution of the kinetic model. The buffer zone is drawn around the kinetic region by introducing a cut-off function, which takes values between zero and one and which is identically zero in the fluid zone and one in the kinetic zone. In the present paper, we specifically consider the possibility of moving the kinetic region or creating new kinetic regions, by evolving the cut-off function with respect to time. We present algorithms which perform this task by taking into account indicators which characterize the non-equilibrium state of the gas. The method is shown to be highly flexible as it relies on the time evolution of the buffer cut-off function rather than on the geometric definition of a moving interface which requires remeshing, by contrast to many previous methods. Numerical examples are presented which validate the method and demonstrate its performances.     

High-flux beam source for cold, slow atoms or molecules

We demonstrate and characterize a high-flux beam source for cold, slow atoms or molecules. The desired species is vaporized using laser ablation, then cooled by thermalization in a cryogenic cell of buffer gas. The beam is formed by particles exiting a hole in the buffer gas cell. We characterize the properties of the beam (flux, forward velocity, temperature) for both an atom (Na) and a molecule (PbO) under varying buffer gas density, and discuss conditions for optimizing these beam parameters. Our source compares favorably to existing techniques of beam formation, for a variety of applications.     

铷光谱灯光谱自吸收现象研究

由自吸收导致的铷光谱灯超精细光谱轮廓变形,对铷原子频标的频率稳定度有不利影响.用F-P干涉仪测量了三种常用铷光谱灯的超精细光谱轮廓,研究了启辉气体种类、压力、谱灯工作温度和激励功率对自吸收的影响.结果表明,充Ar和充Kr谱灯自吸收效应比较显著,充Xe谱灯自吸收不明显;适当增大气体压力、降低灯泡工作温度、增大射频激励功率,可以减小光谱灯的自吸收效应.     

A Quantum-Mechanical Explanation of Buffer Gas Effect on Submillimeter Wave Laser

Based on the theory of molecular vibration relaxation, the model of buffer gas effect was built up. By theoretically deducing the vibrational lower-level deactivation rate of operating gas molecule with quantum mechanics, the selection rules of high-efficient buffer gas under different working conditions were educed and tested by experiments. The results could be helpful to the study of large-power wide-range efficient tunable miniature pulsed optically pumped submillimeter wave laser and its application.     

Stimulated processes in sodium vapour in the presence of molecular buffer gas systems

The influence of hydrocarbon compounds such as methane, ethane and ethylene on collision-induced amplified emission in sodium vapour has been investigated. The intensity dependence of the stimulated resonant emission and stimulated Raman effects on the buffer gas and sodium vapour pressures and the intensity of the excitation radiation has been obtained. The dependence of the stimulated resonant emission bandwidth on the buffer gas pressure has also been measured. It is shown that saturated hydrocarbon molecules can be used as an efficient buffer gas for the generation of stimulated emission in other alkali atoms such as rubidium and caesium.     

Rubidium vapor cell miniaturization-influence on the optical pumping process

We present a comparative study of the optical pumping process in four natural mixture Rb cells with different level of miniaturization. The influence of 2 Torr Ne gas added as buffer on the optical pumping is estimated using the fluorescence spectra on the Rb D₂-line obtained by tunable single-mode circularly-polarized diode laser. The obtained results provide basic information for optimization of alkali-cell dimensions and buffer gas pressure for further coherent spectroscopy based applications.     

High buffer gas pressure perturbation of coherent population trapping in sodium vapors

We report an experimental investigation of coherent population trapping in specially selected Zeeman levels of the sodium atom, performed under high buffer gas pressure in a polydimethylsiloxane coated cell at room temperature. The results show that coherent population trapping will not be completely destroyed when the buffer gas pressure reaches 1100 Torr for He and 1000, 800, and 500 Torr, for Ne, Ar and Kr, respectively. Buffer gases with heavier mass play a larger destructive role for the coherent population trapping. The line width of the dark resonance is reduced with buffer gas pressure. The behavior of the dark resonances on increasing buffer gas is discussed and possible applications are pointed out.     

碰撞对钠分子梯形能级系统高位能级布居的影响

以氩气为缓冲气体,在实验上研究了碰撞过程对钠分子梯形能级系统高位能级两种布居过程的影响。对于双光子激发过程,由于消相碰撞,无多普勒加宽的洛伦兹尖峰随缓冲气体压力的增大而很快消失,加入少量缓冲气体时,碰撞激发过程对以多普勒宽度为特征的信号有一定的增强作用,但加入过量缓冲气体会由于消布居作用使信号减弱,对于主要通过碰撞实现高位能级布居的过程,加入缓冲气体对高位能级布居起关键作用,在速率方程近似下解释了上述结果。     

激光诱导Al等离子体发射光谱特性的实验研究

本文从实验上研究了不同缓冲气体(He,Ar,N2和Air)中激光Al等离子体的时间分辨发射光谱,研究了原子发射谱线的强度和Stark展宽随延时、缓冲气体性质和压力变化的规律.结果表明原子谱线的强度在3μs左右达到最大值,随着延时的增加,谱线的Stark展宽减小,而缓冲气体压力的增大导致谱线的Stark展宽增大,在实验测定的四种缓冲气体中,Ar气体中谱线的Stark展宽最大.     

CuBr脉冲激光动力学模型及其研究

本文通过实验观测CuBr激光等离子体中铜的自发辐射光谱,建立了五能级CuBr脉冲激光动力学模型。应用电子温度和电子密度实验值,通过计算机数值计算得到的激光脉冲波形、峰值时刻、功率等都与实验值基本相符。结果还表明:当输入功率密度不变时,通过改变缓冲气体热扩散步长,可明显改变气体温度或初始铜原子密度,从而改变激光功率。 关键词：     

Structure of 510.6 and 578.2 nm copper laser lines

The structure of the 510.6 and 578.2 nm copper laser lines were calculated and measured as a function of cooper density and buffer gas pressure. The line shapes were consistent with the calculations only near the oscillation threshold. The buffer gas pressure data indicate that the pressure broadening coefficient is very small for our experimental conditions.     

无稀释气立式氧碘化学激光器的设计与实验

 分析了氧碘化学激光器（COIL）在无稀释气条件下工作所带来的一系列问题和对其性能的影响，并提出了相应的解决方法，进而对COIL结构和相关参数进行了有针对性的设计和实验研究。在氯气流量为117.6 mmol/s时,平均输出功率2.25 kW，化学效率达到21.1%，比功率0.22 J/g；分别以氦气和氮气为稀释气，对COIL进行了参数和实验数据比较。     

A laser ion source for on-line mass separation

A laser ion source based on resonance photo ionization in a gas cell is proposed. The gas cell, filled with helium, consists of a target chamber in which the recoil products are stopped and neutralized, and an ionization chamber where the atoms of interest are selectively ionized by the laser light. The extraction of the ions from the ionization chamber through the exit hole and skimmer is similar to the ion-guide system. The conditions to obtain an optimal system are given. The results of a two-step one-laser resonance photo ionization of nickel, and the first results of laser ionization in a helium buffer gas cell are presented.     

Investigation of SRS conversion of XeCl laser emission in lead vapor,methane, and hydrogen

We have thus optimized the conditions for SRS conversion of XeCl-laser emission in lead vapor, methane, and hydrogen. The greatest influence on the conversion efficiency is exerted for an SRS cell with lead by the divergence of the pump radiation, the focusing geometry, and the type of buffer gas. The maximum efficiency with respect to absorbed UV energy was ∼57% when xenon gas was used as the buffer, corresponding to 85% of the photon efficiency. The converted radiation could be continuously tuned in the 457.6–459.3 nm band. Addition of a light gas such as helium or hydrogen to methane raised the efficiency of conversion into Stokes components in methane to ∼24 %.     

锶离子R—M跃迁激光和复合激光的参量研究

在9mm内径和42cm电极间距的石英放电管中，用氦气为缓冲气体，通过纵向快脉冲放电激励，对锶离子红外R—M跃迁激光和蓝色复合激光进行了系统的参量研究.分析和解释了两种谐振腔时各激光谱线输出功率与工作参量（氦压，频率和充电电源电压）的关系曲线，观察和讨论了对应的光电脉冲波形，获得了一组较好的工作参数. 关键词： 脉冲放电激励 锶离子 R—M跃迁激光 复合激光 光电脉冲波形     

Absorption resonances in A-type three-level system in cesium vapor cell with buffer gas

We report experimentally the transformation from the electromagnetically induced transparency (EIT) resonance to a dispersion-like signal and eventually to a nearly symmetric absorption resonance as coupling detuning increases in A-type three-level system in the cesium vapor cell with buffer gas at room temperature. The observed absorption resonance occupies some remarkable properties of the strong amplitude and the narrow linewidth in comparison with the case without buffer gas. The relation between linewidth of the enhanced absorption resonance and buffer gas pressure is studied. With pressure increasing, linewidth of the absorption resonance becomes narrow. The sub-natural linewidth is observed in Doppler-broadened cesium vapor cell in our experiment. The experimental results are in qualitative agreement with the numerical simulations.     

Influence of AlN Buffer Thickness on GaN Grown on Si(111) by Gas Source Molecular Beam Epitaxy with Ammonia

Hexagonal GaN is grown on a Si(111) substrate with AlN as a buffer layer by gas source molecular beam epitaxy (GSMBE) with ammonia. The thickness of AlN buffer is changed from 9 to 72nm. When the thickness of AlN buffer is 36nm, the surface morphology and crystal quality of GaN is optimal. The in-situ reflection high energy electron diffraction (RHEED) reveals that the transition to a two-dimensional growth mode of AlN is the key to the quality of GaN. However, the thickness of AlN buffer is not so critical to the residual in-plane tensile stress in GaN grown on Si(111) by GSMBE for AlN thickness between 9 to 72nm.