Atomic resonance behavior in laser-induced Rb atom desorption—the effect of ambient gas atoms and molecules

We report an observation that in a typical optical pumping cell containing Rb metal and 150 Torr N₂ gas, a cw laser beam of a few tens of mW and beam size 5.5 mm² can desorb Rb films on cell surfaces when the laser is tuned to the Rb D₁ line. The frequency dependence of the Rb desorption rate displays atomic resonance behavior. The desorption is suggested to be mediated by the ambient gas atoms (Rb) and molecules (N₂). The phenomenon was used to provide evidence for the existence of thin Rb films on seemingly clear cell surfaces.     

Hybrid optical pumping of optically dense alkali-metal vapor without quenching gas

Optical pumping of an optically thick atomic vapor typically requires a quenching buffer gas, such as N2, to prevent radiation trapping of unpolarized photons which would depolarize the atoms. We show that optical pumping of a trace contamination of Rb present in K metal results in a 4.5 times higher polarization of K than direct optical pumping of K in the absence of N2. Such spin-exchange polarization transfer from optically thin species is useful in a variety of areas, including spin-polarized nuclear scattering targets and electron beams, quantum-nondemolition spin measurements, and ultrasensitive magnetometry.     

High contrast electromagnetically induced transparency in a nitrogen filled Rb vapour cell

We observe the electromagnetically induced transparency (EIT) spectra inside a nitrogen filled Rb vapour cell (Rb-N₂) in a five-level Λ-type system of D₂ transition of Rb atom. The high contrast EIT resonance in buffer gas filled Rb cell is obtained under our experimental conditions. The effect of velocity changing coherence preserving collisions to obtain the contrast resonance in buffer gas cell has been discussed. We measured the dependence of EIT width and height on pump intensity and find that the EIT width (FWHM) and peak height have a linear dependence on pump intensity. Our experimental results show that the presence of N2 buffer gas reduces the power broadening of the observed resonances.     

Nonlinear resonant polarization rotation under conditions of coherent population trapping

Nonlinear resonant optical rotation was studied over a wide range of experimental parameters at the Rb D ₁ F = 2→F′ = 1 transition in the ⁸⁷Rb vapor under conditions of coherent population trapping. The angle of rotation was found to depend nonmonotonically on the laser intensity and applied magnetic field. The effect of optical pumping out to the level F = 1 is discussed. It is demonstrated experimentally that the Faraday rotation angle increases twofold upon the compensation for pumping.     

Level-crossing-spectroscopy with additional optical pumping in the ground state

The level crossing-technique with additional optical pumping in the ground state is demonstrated in the case of the hyperfinestructure of the 6p ¹ P ₁ state of the two odd isotopes of Yb using a natural occuring isotopic mixture. The influences of the pumping process and of a buffer gas on the lc signal structure are discussed in terms of a modified Breit formula.     

Comparative study of in situ N2 rotational Raman spectroscopy methods for probing energy thermalisation processes during spin-exchange optical pumping

Spin-exchange optical pumping (SEOP) has been widely used to produce enhancements in nuclear spin polarisation for hyperpolarised noble gases. However, some key fundamental physical processes underlying SEOP remain poorly understood, particularly in regards to how pump laser energy absorbed during SEOP is thermalised, distributed and dissipated. This study uses in situ ultra-low frequency Raman spectroscopy to probe rotational temperatures of nitrogen buffer gas during optical pumping under conditions of high resonant laser flux and binary Xe/N₂ gas mixtures. We compare two methods of collecting the Raman scattering signal from the SEOP cell: a conventional orthogonal arrangement combining intrinsic spatial filtering with the utilisation of the internal baffles of the Raman spectrometer, eliminating probe laser light and Rayleigh scattering, versus a new in-line modular design that uses ultra-narrowband notch filters to remove such unwanted contributions. We report a ~23-fold improvement in detection sensitivity using the in-line module, which leads to faster data acquisition and more accurate real-time monitoring of energy transport processes during optical pumping. The utility of this approach is demonstrated via measurements of the local internal gas temperature (which can greatly exceed the externally measured temperature) as a function of incident laser power and position within the cell.     

Resonance transition 795-nm rubidium laser using He buffer gas

We report a demonstration of a 795-nm rubidium optical resonance transition laser using a buffer gas consisting of pure ³He. This follows our recent demonstration of a hydrocarbon-free 795-nm rubidium resonance laser which used naturally-occurring He as the buffer gas. Using He gas that is isotopically enriched with ³He yields enhanced mixing of the Rb fine-structure levels. This enables efficient lasing at reduced He buffer gas pressure, improved thermal management in high average power Rb lasers and enhanced power scaling potential of such systems.     

基于振动弛豫理论提高光抽运太赫兹激光器输出功率的研究

以半经典密度矩阵理论和分子振动弛豫理论为基础,研究添加适当比例缓冲气体与适当减小波导芯径对光抽运太赫兹激光器输出光强的影响.计算结果表明,加入适当比例缓冲气体或适当减小波导的芯径均能提高太赫兹激光的输出光强;同时优化两个参数能进一步提高抽运激光能量转化为太赫兹激光能量的效率,延长工作腔中的有效激活区,延缓抽运饱和效应的出现,提高太赫兹激光输出光强.该研究对提高光抽运太赫兹激光器的能量转化效率、提高光抽运太赫兹激光器的输出功率及实现光抽运太赫兹激光器的小型化有重要的指导意义.     

光抽运实验中的微波-射频多量子跃迁

在⁸⁷Rb气泡光抽运实验中,我们同时用微波场和射频场作用在⁸⁷Rb原子上,观察到了⁸⁷Rb原子基态微波-射频多量子跃迁的光检测共振谱线。 关键词：     

Slow spin relaxation of Rb atoms confined in glass cells filled with dense 4He gas at 1.85 K

At temperatures below 2.1 K, long-lived gaseous Rb atoms in glass cells have been generated with a simple method: irradiating the cells, containing 4He gas and Rb metal, with a cw laser. The obtained atomic Rb density ( approximately 10(8) cm(-3)) decreases with a 1/e time constant of about 10 s at 1.85 K. We have performed optical pumping of the Rb atoms and measured the longitudinal electronic spin relaxation time at 1.85 K as well. For processes (such as Rb-He collisions) which do not remove the atomic Rb from the vapor, this relaxation time is found to be about 60+/-15 s.     

High capacity production of >65% spin polarized xenon-129 for NMR spectroscopy and imaging

A rubidium spin exchange optical pumping system for high capacity production of >65% spin polarized 129Xe gas is described. This system is based on a fiber coupled multiple laser diode array capable of producing an unprecedented 210 W of circularly polarized light at the pumping cell with a laser line width of 1.6 nm. The 129Xe nuclear spin polarization is measured as a function of flow rate, pumping cell pressure, and laser power for varying pumping gas compositions. A maximum 129Xe nuclear polarization of 67% was achieved using a 0.6% Xe mixture at a Xe flow rate of 2.45 sccm. The ability to generate 12% polarized 129Xe at rates in excess of 1L-atm/h is also demonstrated. To achieve production of 129Xe gas at even higher polarization will rely on further optimization of the pumping cell and laser beam geometries in order to mitigate problems associated with temperature gradients that are encountered at high laser power and Rb density.     

Collision induced dissociation of Cs2 studied by atom-molecule-exchange optical pumping

Using the atom-molecule-exchange optical pumping method the collision induced dissociation of Cs₂ in the foreign gas atmospheres He, Ne, Ar, Kr, N₂ and CH₄ is studied. The rate constant for dissociation is found to have an Arrhenius form and good agreement of the activation energy with the spectroscopically determined bond dissociation energy is obtained.     

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。     

Nuclear spins of76Rb and119Cs byβ radiation detected optical pumping

An optical pumping apparatus has been attached to the reconstructed ISOLDE on-line mass separator at CERN in order to obtain nuclear data of isotopes far fromβ stability. As first results the spins of⁷⁶Rb (T _1/2=36.8 s) and¹¹⁹Cs (T _1/2=37.7 s) have been determined byβ radiation detected optical pumping (β-RADOP) to beI=1 andI=9/2 respectively.     

Saturation spectroscopy of hydrogen 1-011-011-01lines with a multi-mode cw dye laser

With an intense, broadband multi-mode cw dye laser collisional studies of H_α fine-structure resonances with saturated absorption are extended to He buffer gas pressures larger than 30 mbar (0°C). The broadening and shift of the two prominent H_α(2P?3D) transitions are measured in a (He+4% H) gas discharge. The absolute magnitude and the differences in the width of the lines are explained theoretically by different inelastic fine-structure transfer cross sections which can also be deduced from the pressure effect data. Nuclear polarization of hydrogen atoms by H_α optical pumping and polarization transfer to the H(1S) ground state via Ly-α decay and further applications of the multimode laser are discussed.     

85Rb灯对87Rb原子的光抽运

本文对用⁸⁵Rb灯不经滤光泡直接对⁸⁷Rb吸收泡的光抽运作了观测,得到了比传统的用⁸⁷Rb灯经⁸⁵Rb滤光泡对⁸⁷Rb吸收泡进行光抽运更强的基态0—0跃迁共振讯号。并在一定温度下观察到负的共振讯号。到目前为止,还不能对这种负的共振讯号作出解释。同时还测量了共振线宽和光频移。对在⁸⁷Rb原子频标中应用的可能性作了评述。 关键词：     

Velocity selective optical pumping and repumping effects with counter and copropagating laser radiations for D<Subscript>2</Subscript> lines of rubidium

The effects of a strong control or pump laser, counter propagating or copropagating with the probe beam, on the probe absorption spectra of ⁸⁵Rb and ⁸⁷Rb-D₂ transitions have been investigated inside a room temperature Rb vapour cell. In both cases a set of strong velocity selective resonance dips are observed at different velocities. Their movements across the Doppler broadened probe absorption profile have been studied for different lock frequencies of the control laser. These spectra are modified by optical pumping effects due to the presence of another hyperfine component of the ground state. A repumping laser, from the dark hyperfine component of the ground level transfers almost 75% of the atoms from the dark state to the pump probe cycle hence reducing the optical pumping effect. A numerical simulation is done to explain the observed spectra. The effect of a control laser on the Lamb dip spectrum of the probe laser has also been investigated. The control beam is used to improve the strength of a weak hyperfine dip on the Doppler broadened probe spectrum. The strength of the hyperfine dip increases by a factor of 3.2 in presence of the control laser. The observed dips show that pump-probe spectroscopy can be used as velocity selectors of atoms.     

Improved gain for the Ar 2 * excimer laser at 126 nm

Argon was excited by intense electron beam pumping. The optical gain obtainable in Ar ₂ ^2* at 126 nm was investigated as a function of gas pressure and pumping density. The gas pressure necessary to achieve a gain of 10%/cm is reduced from 3.2 to 1.0 MPa if the gas is cooled at 170 K. The effect is partly due to reduced absorption by the removal of impurities. The results allow one a new approach to construct high-power lasers in the vacuum ultraviolet below 150 nm.     

Polarization spectroscopy of Rb and Cs

Theoretical calculation of ⁸⁵Rb and ¹³³Cs D₁ signals in polarization spectroscopy is presented by using the method of velocity-selective optical pumping in a four-level system. Since good agreement between theory and experiment has been found in Na D₁ polarized signals, the theoretical calculation can be also applied to Rb and Cs D₁ lines. Rb and Cs atoms have higher total angular momentum F in the hyperfine structures than Na atom and then the calculation is more complicated. The relative signal intensities in polarization spectroscopy are compared with those in saturation spectroscopy.     

Influence of transverse magnetic fields and depletion of working levels on the nonlinear resonance Faraday effect

The nonlinear resonance Faraday effect is studied under the condition of coherent population trapping in ⁸⁷Rb vapor at the D₁-line F=2→F′=1 transition. The influence of transverse magnetic fields on the nonlinear optical Faraday rotation is studied. For the transverse fields perpendicular to the electromagnetic-wave polarization, a simple theoretical model is proposed, which is in good agreement with experimental data. The optimal intensity providing the maximum sensitivity is found based on the results obtained. The influence of working-level depletion on the parameters of Faraday rotation in open systems is studied experimentally and theoretically. The system was closed in the experiment by using an additional laser to increase the sensitivity and extend the dynamic range of measured fields. The importance of compensating for the depletion in the presence of spurious magnetic fields is shown; in particular, the sensitivity was enhanced by a factor of 50 in experiments with a buffer gas.