Transition In Cesium Research Articles

Measurement of the dc Stark shift of the 6S[over →]7S transition in atomic cesium

We have measured the dc Stark shift of the $6\stackrel{\ensuremath{\rightarrow}}{S}7S$ transition in atomic cesium using laser spectroscopy. The result of our experiment is $0.7262(8){\mathrm{Hz}\mathrm{}(\mathrm{V}/\mathrm{c}\mathrm{m})}^{\mathrm{\ensuremath{-}}2}.$ This value disagrees with a previous experiment but is within 0.3% of the value predicted by ab initio calculations. This measurement removes the largest outstanding disagreement between experiment and ab initio theory of low-lying states in atomic cesium.

Blackbody Excitation of an Atom Controlled by a Tunable Cavity

We have used a gold cavity to control the blackbody spectrum and hence to alter thermal excitation of a Rydberg atom. We suppress the cesium transition $13S\ensuremath{-}13P$ or $14S\ensuremath{-}14P$ when the cavity width is less than half the transition wavelength, 37 or $50\ensuremath{\mu}\mathrm{m}$. Our measurements resolve the fine structure to a few percent. The experimental curves can be understood by summing multiple reflections of the atomic dipole in the walls of the cavity. Changing the temperature shows explicitly that the excitation rates are indeed proportional to the number of photons per mode of the blackbody field.

Amplification of atomic L-R asymmetries by stimulated emission: experimental demonstration of sensitivity enhancement valuable for parity violation measurements

While all Atomic Parity Violation experiments on highly forbidden transitions in a Stark field have used the detection of fluorescence signals, our group is engaged in an experiment on the \(\) cesium transition that uses a pump-probe scheme. The role of the probe beam is to detect the 7S state by stimulated emission. The detected Left-Right asymmetry (\(\)) appears directly on the transmitted probe beam and the technique relies on differential-mode atomic polarimetry. We present here experimental results which illustrate two essential features of this approach. First, \(\) is amplified when the optical thickness for the probe beam is increased, hence it is an increasing function of the Stark field. Secondly, the experimental sensitivity to \(\) is simultaneously increase d, as demonstrated by our measurements of the signal-to-noise ratio. We emphasize also the advantage of choosing a probe transition that involves a “dark” state: the \(\)amplification is preserved at high levels of the probe intensity because saturation effects are greatly reduced.

X-ray laser scheme driven by two laser pulses

A study is presented to find a compact X-ray laser in the spectral range of the water window. A double laser pulse method that requires a minimum energy with an optimal timing is proposed. The precreated plasma with an optimal ion distribution is heated by a short second pulse creating the required population inversion. In particular, the Ni-like 4d→4p transitions in tantalum, tungsten, and cesium are calculated.

A T not P violating polarization dependence in the stimulated Raman effect

We put forward a new optical experiment which is sensitive to atomic T-violation, not accompanied by parity non-conservation. Our proposal is a polarization dependence of the form in the off-resonance stimulated Raman effect using two plane-polarized light beams a and b with polarizations and . We show how T-odd admixtures lead to this effect which changes sign with the sign of the magnetic quantum numbers of the states involved but is identical for the forward and backward process between the same states. We examine the ratio of the T-odd to the normal Raman effects as a function of the off-set of an intermediate resonance and find no significant enhancement as a function of frequency. There is a rapid variation of this ratio in the resonance region, but we note that in this region there can be competing effects due to the decay of the intermediate state. As an example of our general analysis, we apply our results to the hyperfine Raman transition in caesium with the lasers assumed near but off-set from the transition. We assume a model T-violation in which the nearby state is admixed into the . We express the T-odd Raman polarization in terms of the admixed amplitude of the state and show that the fractional polarization is of order the T-odd state admixture, and that no enhancement is likely. We leave the feasibility of an experiment to future study.

Frequency metrology by use of quantum interference

Quantum interference in the rate of two-photon excitation of the 6S((1/2)) ?6P(3/2) ? 6D(5/2) transition in atomic cesium is exploited to demonstrate phase-sensitive frequency demodulation for an optical interval of +/- 12.5 THz. By thus using atoms as ultrafast nonlinear mixing elements, we suggest and analyze a new avenue for absolute comparisons of a dense set of frequencies over the range of 200-2000 nm.

Two-photon selective reflection.

The conditions of observation of direct two-photon-induced dispersion in three-level reflection spectroscopy at a vapor-dielectric interface are discussed. One shows how pump frequency modulation allows one to discriminate the two-photon singular contribution associated with atoms moving quasiparallel to the dielectric interface, and therefore single out off-resonant Doppler-free two-photon dispersion in selective reflection. A nonperturbative theoretical approach to two-photon reflection is shown to predict a dynamic Stark shift of the two-photon resonance, which has been experimentally observed on the 6S-6P-8S transition of cesium. \textcopyright{} 1996 The American Physical Society.

Doppler-free excitation of the weak 6 S 1/2 -8 P 1/2 cesium transition at 389 nm

We report the resolution of the hyperfine structure of the 6S1/2-8P1/2 Cs transition by means of laser saturation spectroscopy. This transition is anomalously weak as discussed by zu Putlitz in 1969. The metrological potentialities of this narrow line are illustrated together with a possible scheme for a direct frequency measurement.

Measurement and modelling of intensity dependent absorption and transit relaxation on the cesium line

The intensity dependent absorption was measured on the line (6 transition) in atomic cesium. The magnetic field applied to the vapour and the spatial cross section of the laser beam were controlled and varied during data collection. A three-level rate equation model is presented in an attempt to explain the results. We show that this well known approach does not sucessfully model the data obtained in the absence of a magnetic field. Hence, a more complex and complete model that explicitly includes all of the hyperfine magnetic sublevels (a multilevel model) is presented. This approach accurately models all of the data collected. The good agreement betweeen this model and the data allows the determination of the transit relaxation rate (due to atomic time of flight through the laser beam), , where is the two-dimensional root-mean-squared speed of the atom and D is the FWHM of the Gaussian laser beam spatial profile.

Amplification of electroweak left-right asymmetry in atoms by stimulated emission

This work describes quantitatively the amplification of the electroweak left-right asymmetry, a remarkable and attractive feature of the experiment in progress on the 6S1/2 → 7S1/2 cesium transition using detection by stimulated emission on the 7S1/2 → 6P3/2 transition. The process relies on the optical anisotropy of the atomic medium resulting from the 7S1/2 alignment created by excitation with linearly polarized light. The crucial parameter (α⊥−α∥)/α∥ involves the amplification coefficients for the probe field oriented in a direction either parallel or perpendicular to the alignment axis. Explicit computations are done by a semiclassical approach (classical for the field, quantum mechanical for the atomic states). The larger the optical anisotropy and the optical density, the stronger the asymmetry amplification; among all hyperfine components of the 7S1/2 → 6P3/2 transition, the ΔF=0 ones and more particularly the 4 → 4 offer the largest anisotropy. It is also predicted that saturation of the probe transition by the optical field should provide manifestation of the effect at lower optical densities and notwithstanding at larger fluxes of transmitted photons. Indirect production of 6P3/2 atoms by the excitation pulse does not reduce the left-right asymmetry, neither its amplification which then appears at lower effective optical densities.

Absorption spectroscopy of N_2O with phase-diffusion-noise sidebands on a lead-salt tunable diode laser

The broad phase-diffusion-noise spectrum of a lead-salt tunable diode laser (TDL) has been exploited for the detection of absorbances produced from low-pressure N(2)O vapor in the 4.47-µm spectral region. This effect has previously been observed in the detection of electronic transitions in rubidium, cesium, and molecular oxygen with anAlGaAs TDL operating in the 0.700-0.800-µm region. For the first time to our knowledge, this paper presents evidence of this phenomenon when a midinfrared rovibrational absorption line is monitored. The technique is also compared with traditional TDL spectroscopic methods for its applicability to trace-vapor monitoring.

Precision measurement of Stark shifts for 6P3/2-->nS1/2 n=10-13 transitions in cesium.

The Stark shifts of four transitions in cesium were measured using two atomic beams. One traverses through a uniform electric field and the other a field-free region. The atoms were excited using a ring dye laser, with the laser beam interacting with the atoms in the electric-field region frequency shifted by an acousto-optic modulator. The Stark shift was determined by measuring the electric field for which the atoms in both beams are simultaneously in resonance. The results for the 6${\mathit{P}}_{3/2}$\ensuremath{\rightarrow}(10--13)${\mathit{S}}_{1/2}$ transitions are -59.36(14), -154.68(13), -356.57(29), and -745.43(61) MHz (kV/cm${)}^{2}$, respectively.

Electronic states and the metal–insulator transition in caesium–ammonia solutions

The nature of the electronic states in caesium–ammonia solutions is examined from the insulating to the metallic regime using two different microscopic models (Z. Deng, G. J. Martyna and M. L. Klein, J. Chem. Phys., 1994, 100, 7590.). In the first model, the ammonia molecules are treated via a classical point-charge model and the cations as a positive neutralizing background. In the second model, the ammonia solvent is made fully polarizable and the cations, here caesium, are explicitly included. The solvent and ions are treated classically and the electronic degrees of freedom are handled using the Car–Parrinello method and density functional theory. At 260 K, the models give the following picture of the electronic states as a function of caesium/electron concentration: The dilute solution behaves like an electrolyte in which the electrons exist as polarons, on average spherical states localized in solvent cavities, far from the counter ions. At ca. 0.5 mol % metal (MPM), the solvated electrons are spin-paired and form large peanut-shaped species called bipolarons. The electrons still exist as bipolarons at ca. 1 MPM but well separated from each other. The bipolarons exhibit no strong tendency to be oriented either parallel or perpendicular to each other. We have investigated the effect of system size on the structure and dynamics of the bipolarons at ca. 1 MPM and found it to be small. At higher concentration, ca. 2 MPM, the electrons exhibit a tendency to cluster and the electron density oscillates between localized and delocalized states. At much higher concentration, ca. 9 MPM, the solution behaves as a good liquid metal in which the electron density forms multi-tunnel-like extended states. The caesium cations are always solvated by the ammonia and are thereby isolated from close contact with the electron density. The role of the cations is assessed through a comparison of the results of the two models. At low metal concentration, the effect of the cations turns out to be rather small. However, the explicit inclusion of the ions is found to increase the metallic character of the solution at ca. 9 MPM. Our findings rationalize a large body of experimental data on this system.

The adiabatic thermal pressure coefficient of expanded liquid alkali metals

The heat capacity of liquid caesium at high temperatures up to 1800 K and pressure 0.1 mPa has been measured by periodic heating method and adiabatic thermal pressure coefficient for study of structural transition in liquid caesium at temperature ∼ 570 K. The revealed analogy of ( ϖT/ ϖp) s dependence on temperature is discussed as a fact confirming the existence of structure factor changes in this region.

Measurement of the 6p2P3/2 state lifetime in atomic cesium.

We present a precision experimental test of atomic many-body theory that is currently applied to the interpretation of recent parity-nonconservation experiments in atomic cesium. We report the first measurement of the $^{133}\mathrm{Cs}$ 6p $^{2}$${\mathit{P}}_{3/2}$ state lifetime using resonant diode-laser excitation of a fast atomic beam. The lifetime result of 30.55\ifmmode\pm\else\textpm\fi{}0.27 ns determines the absorption oscillator strength for the 6s $^{2}$${\mathit{S}}_{1/2}$--6p $^{2}$${\mathit{P}}_{3/2}$ transition in cesium to be 0.7133\ifmmode\pm\else\textpm\fi{}0.0064, and establishes the accuracy of recent relativistic many-body calculations of the dipole transition matrix element to 0.5%.

A driver for stable-frequency operation of laser diodes

A driver for the stable-frequency operation of an AlGaAs laser diode is described. This consists of a constant current source with short-term fluctuations of ±8 μA and a drift of less than 2 μA in 10 h, in conjunction with a ±1 mdeg temperature controller. The current can be set to values up to 100 mA and a ramp current up to 20 mA can be added to this to allow frequency scanning of the laser. The laser linewidth is measured by heterodyning two such stabilized lasers and recording the beat note. This has a width of 27±7 MHz. The frequency drift is monitored by exciting the D2 transition of cesium and recording the change in absorbed power when a laser is tuned to the side of an absorption peak. The drift is measured to be 10 kHz/s over 5 h, and is attributed largely to temperature drift. In addition, the current circuit can be readily interfaced to a microcomputer for automatic control of the laser current without sacrificing stability.

High-accuracy calculation of parity nonconservation in cesium and implications for particle physics.

High-precision measurements of atomic parity-nonconserving transitions in cesium when coupled with calculations of similar accuracy allow for a precise determination of ${Q}_{W}$, the weak nuclear charge. When expressed in terms of the $Z$ mass, radiative corrections to ${Q}_{W}$ are insensitive to the top-quark mass, so such a determination of ${Q}_{W}$ allows a particularly sensitive probe of radiative corrections depending on new physics. While the wave function of cesium, the atom in which the most accurate measurements have been made, is extremely complex, atomic theory has advanced to a point where predictions accurate to 1% can be made. This paper describes such a calculation with particular emphasis on the question of the reliability of the atomic theory. Particle-physics implications following from the present state of theory and experiment are discussed, and prospects for more accurate work described.

Studies of the optogalvanic effect in a commercial caesium hollow cathode lamp and its use for tuning pulsed dye lasers

The use of the optogalvanic effect (OGE) in a hollow cathode lamp for wavelength tuning of dye lasers is an established technique at laser wavelengths longer than ∼ 560 nm, corresponding to photon energies less than ∼ 2.2 eV. This work describes the first successful optogalvanic studies on caesium at higher photon energies. Once set up, OGE in a standard commercial hollow cathode lamp provides a quick and cheap means of tuning a continuously tunable laser to a chosen atomic transition. The 6 2S 1 2 → 7 2P 3 2 , 1 2 lines in caesium at 455.55 nm and 459.32 nm were resolved. This work is also believed to be the first to describe the detection of any caesium transition using the optogalvanic effect in a commercial hollow cathode lamp, rather than a specially constructed tube. The method used is applicable to other materials which have previously proved difficult.

Intensity-dependent polarization correlations in the field-free 6S to 7S to 15P two-photon transition of caesium

The authors investigated the resonant M1-E1 two-photon transition (6S12/ to 7S12/ to 15P32/) in caesium using counterpropagating single-mode laser beams in a thermionic diode. They measured circular polarization correlations, i.e. the dependence of the two-photon transition rate on the relative helicities of the two circularly polarized beams. The results depend strongly on the intensity of the laser driving the 7S to 15P transition and are in good agreement with theoretical predictions from a rate equation treatment taking collisional population redistributions among the 15p32/ states into account. The implications of the results for a field-free parity violation experiment are discussed.

Cs(VI): A new high-pressure polymorph of cesium above 72 GPa.

A new structural phase transition in cesium has been found around 72 GPa using high-pressure powder x-ray-diffraction techniques with a diamond-anvil cell and an imaging plate. The crystal structure of the high-pressure phase Cs(VI) is either hexagonal close packed or double hexagonal close packed. The transition from the open-packed Cs(V) structure to the close-packed Cs(VI) structure implies significant influence of the 5p core repulsion to the cohesion of Cs(VI), as well as a possible occurrence of the 5p-5d overlap.