Relaxation of quadrupole orientation in an optically pumped alkali vapour

Summary The relaxation of quadrupole orientation (alignment) in an optically pumped alkali vapour is theoretically studied by taking into account the relaxation processes by alkali-buffer gas, alkali-alkali with spin exchange and alkali-cell wall (diffusion process) collisions. The relaxation transients of the quadrupole orientation are obtained by introducing a first-order weak-pumping approximation (intermediate pumping) less restrictive than the usually considered (zeroth order) one.

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Riassunto Il rilassamento dell’orientamento quadrupolare (allineamento) di un vapore alcalino pompato otticamente è studiato dal punto di vista teorico prendendo in considerazione i processi di rilassamento mediante collisioni base alcalina-gas tampone, base alcalina-base alcalina con scambio di spin e base alcalina-parete della cella (processo di diffusione). I transienti di rilassamento dell’orientamento quadrupolare sono ottenuti introducendo un’approssimazione di prim’ordine con pompaggio debole (pompaggio medio) meno restrittiva di quella considerata solitamente (di ordine zero).

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Резюме Теоретически исследуется релаксация квадрупольной ориентации в оптически накаченных парах щелочных металлов, учитывая релаксационные процессы взаимодействия буферного газа и атомов щелочного металла, столкновения атомов щелочного металла между собой с изменением ориентации спина и столкновения атомов щелочного металла со стенкой ячейки (процесс диффузии). Обнаружены релаксационные переходные процессы для квадрупольной ориентации, вводя промежуточную накачку.

     

Highly efficient optically pumped cesium vapor laser

We have demonstrated an optically pumped continuous wave Cs vapor laser with an input power to output power slope efficiency of 81%. The laser power was 0.35 W for an input power of 0.57 W, yielding an overall optical efficiency of 63%.     

光泵铯蒸气激光的动力学模型

建立了一个物理模型描述了光泵铯蒸气激光的动力学过程和激光机理.结合实验参量,经数值求解该模型,定量分析了抽运光参量、缓冲气压和输出镜反射率等对激光输出功率和光光效率产生的影响,得到了与实验基本一致的模拟结果.表明该模型较好地反映了光泵銫蒸气激光的动力学机理和发射过程,为该类激光的优化设计提供了借鉴和参考.     

高强度泵浦碱金属蒸气激光器的光参量振荡器

以电光调Q的Nd:YAG激光器为泵浦源,以磷酸氧钛钾（KTP）为非线性晶体,搭建了调谐范围为750~800 nm的光参量振荡器。信号光在中心波长780.2 nm处获得单脉冲能量113 mJ、脉宽15.43 ns、光斑直径5.5 mm的输出。用光栅单色仪测量信号光光谱宽度（FWHM）为0.38 nm。信号光通过120 ℃的铷蒸气池,观察到清晰的荧光轨迹。证明信号光能有效泵浦铷蒸气,可为铷激光器提供峰值功率7 MW的高强度脉冲泵浦源,进而研究铷激光器在高强度泵浦条件下的动力学过程和基础物理机制。     

高强度泵浦碱金属蒸气激光器的光参量振荡器

以电光调Q的Nd:YAG激光器为泵浦源,以磷酸氧钛钾（KTP）为非线性晶体,搭建了调谐范围为750~800 nm的光参量振荡器。信号光在中心波长780.2 nm处获得单脉冲能量113 mJ、脉宽15.43 ns、光斑直径5.5 mm的输出。用光栅单色仪测量信号光光谱宽度（FWHM）为0.38 nm。信号光通过120 ℃的铷蒸气池,观察到清晰的荧光轨迹。证明信号光能有效泵浦铷蒸气,可为铷激光器提供峰值功率7 MW的高强度脉冲泵浦源,进而研究铷激光器在高强度泵浦条件下的动力学过程和基础物理机制。     

Visible superfluorescence from optically pumped europium atoms

We have observed superfluorescence (SF) on five atomic transitions at visible wavelengths 633.58, 635.00, 640.09, 640.61 and 736.22 nm in Doppler broadened gas of europium (Eu) atom. The nanosecond SF pulses were observed by longitudinally pumping Eu vapor column with a pulsed dye laser to upper states 4f⁶5d6s², ⁸D_7/2at 346.79 nm and 4f⁷5d6p, ¹⁰F_5/2at 348.73 nm from the ground state 4f⁷6s², ⁸S_7/2. High optical conversion efficiency ≈10% was measured for these SF transitions. Our experiment deals with the large sample multilevel SF in the regime where the length of the excited column L is greater than the maximum value of the Arecchi-Courtens length (L_c). The observed variation of SF peak intensity (I_fl) and time delay for SF evolution (τ_D) with number of atoms in the excited state (N) resemble theoretically predicted SF scaling laws for transverse excitation, namely I_fl∝N and t_D μ 1/?N\tau_D \propto 1/{\sqrt N} although the experimental condition is similar to the swept excitation. This could be due to the Rabi frequency associated with the pump transition which is comparable to the SF delay time precluding the initiation of SF at different times along the sample and results in transverse (instantaneous) excitation. The experimental τ_D values were found to be in agreement with the quantum mechanical calculations describing SF.     

Effects of partial decoupling of electronic and nuclear spin on the relaxation of an optically pumped alkali vapour

Summary The effects of a static magnetic field on the relaxation of an alkali vapour by isotropic collisions with very short correlation time are studied. relaxation transients are specifically considered. The analytical approach to the problem allows us to get the number and structure of eigenobservables, both the subset of degenerate eigenobservables, whose relaxation is not affected by the magnetic field, and the subset of nondegenerate eigenobservables with magnetic-field-dependent relaxation rates. First-order approximations to modified relaxation rates are also analytically derived.

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Riassunto Si studiano gli effetti di un campo magnetico statico sul rilassamento di un vapore alcalino mediante collisioni isotrope con tempo di correlazione molto breve. L’approccio analitico al problema ci permette di ottenere il numero e la struttura di autoosservabili, sia il sottogruppo delle autoosservabili degenerate, il cui rilassamento non è influenzato dal campo magnetico, sia il sottogruppo di autoosservabili non degenerate con valori di rilassamento dipendenti dal campo magnetico. Si derivano anche analiticamente approssimazioni di prim’ordine ai valori di rilassamento modificati.

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Резюме Исследуется влияие статического магнитного поля на релаксацию пароь щелочных металлов в результате изотропных соударений с очень малым временем корреляции. В частности, рассматривается релаксационный переходной процесс. Аналитический подход к проблеме позволяет получить число и структуру собственных значений: подсистему вырожденных собственных величин, релаксация которых не зависит от магнитного поля и подсистему невырожденных собственных значений, для которых релаксация зависит от магнитного поля. Аналитически выводятся приближения первого порядка для модификации релаксационных переходов.

     

Strong resonance reflection of polarized light from an alkali vapor

Resonance reflection of light from the interface between a dielectric and an alkali vapor is studied. Two cases are considered in which a laser light beam is polarized either parallel or perpendicular to the plane of incidence. Upon scanning of the frequency of the incident laser radiation, in the first case, the reflection conditions vary from approximately the conditions of Brewster reflection to the conditions characteristics of total internal reflection. In the second case, the Brewster reflection conditions are not realized, and the variations in the intensity of the reflected light observed upon frequency scanning are smaller. The rotation of the plane of polarization and the laser frequency tuning make it possible to rapidly switch between these reflection conditions.     

Anisotropic gain in an optically pumped cw FIR laser

The observed asymmetry of tuning curves of a 70.6 μm CH₃OH laser is interpreted as a consequence of unidirectional amplification in the optically pumped gas, a quantum mechanical double resonance effect. The occurrence of this effect. was verified by FIR gain measurements.     

Nuclear magnetic resonance of K2 in optically pumped potassium vapor

Nuclear spin polarization in diatomic potassium molecules is produced by polarization transfer between dimers and optically pumped potassium atoms. NMR signals from K₂-molecules have been measured. Linewidth studies give information on relaxation processes of nuclear magnetic polarization.     

The wavefront curvature of an optically pumped waveguide laser

Summary A procedure for computing the shape of the wavefronts in waveguide lasers with inhomogeneous gain has been found. Its application to an optically pumped FIR laser shows that the inhomogeneous pump beam intensity will lead to sizeable effects in the output beam geometry.The same treatment is possible for other types of waveguide lasers, too. It is probable that in most cases the first order approximation is satisfactory. If waveguide losses have to be included, this can easily be accounted for by replacing G in equation (4) by (G-).     

Dispersion in a cw optically pumped FIR laser

Direct frequency measurements of a¹³CO₂/¹⁵NH₃ OPFIRL output show that laser pulling effects give shifts of a few MHz, which agree well with a density matrix calculation.     

Tunable far-infrared radiation from optically pumped potassium Rydberg transitions

We report the generation of tunable far-infrared radiation by the optical pumping of potassium metal vapor to the13p Rykberg state. Subsequent cascade by stimulated emission is measured at several wavelengths between 76 and 146 cm^–1 with a conversion quantum efficiency of greater than 10 percent. Emission observed in this region are tuned up to 18 GHz by the application of a pulsed Stark field across a parallel-plate heat pipe. Cascade branching to the 11d to 10f transition at 146 cm^–1 is observed which can be tuned up to 7 cm^–1 in our device. Similar branching following excitation up to the 18 p state is shown to provide almost complete tunability in the far-infrared region.Work performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under contract number W-7405-ENG-48.     

The equilibrium polarization of an optically pumped3He target

The nuclear polarization of an optically pumped³He target can be determined by optical methods if one makes some assumptions on the kinetics of the pumping process. Experiments and calculations have been carried out to examine whether these postulates are permissible. A good agreement between experiments and theory confirms the correctness of the assumptions and consequently justify the determination of the nuclear polarization by optical methods.     

New FIR laser lines from optically pumped methanol analogues

Several new laser lines using optically pumped deuterated methanol molecules have been discovered. These not only increase the spectral coverage of pumped methanol isotopes but may assist in the assignment of a molecular structure.     

Frequency stability of an optically pumped cesium beam frequency standard

Results obtained in an experimental optically pumped cesium beam frequency standard in which a single semiconductor laser is used for the state selection and the atom detection are reported. The separation between the two interaction regions is equal to 21 cm. This gives a 500 Hz linewidth which is observed with a signal to noise ratio equal to 10,000 in a 1 Hz noise bandwidth. A quartz crystal oscillator is frequency controlled by the atomic transition. The measured short term frequency stability is given by _y()=2×10^–12–1/2 for 1 s<500 s. Prospects for improvement of this frequency stability are discussed.