Effect of the polarization of counterpropagating light waves on nonlinear resonances of the electromagnetically induced transparency and absorption in the Hanle configuration

A polarization method has been proposed for transforming the nonlinear electromagnetically induced transparency resonance into the electromagnetically induced absorption resonance (and vice versa) in the Hanle configuration in the field of counterpropagating waves. Numerical calculations have been performed for the F _g = 2 → F _e = 1 and F _g = 2 → F _e = 3 transitions in the ⁸⁷Rb atom. The qualitative analysis of the effect has been performed for the three-level Λ scheme of the atomic energy levels. The main theoretical conclusions are in qualitative agreement with our experimental data for ⁸⁷Rb. The results can be applied in magnetometry and nonlinear optics.     

Nonlinear Hanle effect in Cs vapor under strong laser excitation

We report results of a theoretical and experimental study of the ground state nonlinear Hanle effect under strong laser excitation. It is shown that besides the well-known zero-magnetic field suppression of absorption on F _g = F→F _e = F - 1 transitions caused by population trapping, an optical pumping induced enhanced absorption occurs on F _g = F→F _e = F + 1 transitions for small B-fields. The latter effect becomes more pronounced for high F values. The experiment with atomic vapor of Cs (D₂ line, F _g = 4) confirms an increase of the spectrally unresolved fluorescence yield at zero magnetic field and 600 mW/cm² laser intensity by 9% or 42%, when excitation occurs with linearly or circularly polarized light, respectively. The results of the experiment agree with numerical simulation studies using equations of motion for a density matrix. Received 24 November 2001 / Received in final form 25 March 2002 Published online 24 September 2002     

Influence of the neighboring transition on polarization gradient cooling

g =4→F_e ^′=5 transition. As the detuning becomes larger, the equilibrium temperature becomes lower. When the detuning is larger than 150 MHz, the influence of the F_g=4→F_e ^′=4 transition also becomes significant. We show our numerical analysis of polarization gradient cooling, taking into account actual sublevels of the ground state and two excited states. We conclude that it is preferable to use a detuning of greater than 180 MHz, to get both a high deceleration and low equilibrium temperature. Received: 25 September 1996/Revised version: 10 January 1997     

Laser frequency stabilization using a balanced bi-polarimeter

We report on a Doppler-free polarization spectroscopy based technique of laser frequency stabilization using a balanced bi-polarimeter set-up. Two linearly polarized weak laser beams are used to probe birefringence induced by two oppositely circularly polarized strong pump beams in a vapour cell. Subtraction of balanced polarimeter signals obtained from the two probe beams results in a background-free dispersion-like reference signal without frequency modulation. The dispersion-like signal corresponding to the closed transition 5 ² S _1/2 (F=2) →5 ² P _3/2 (F^′=3) of ⁸⁷Rb was used for frequency locking of a diode laser. The frequency fluctuations and the drift were measured to be less than 0.25 MHz and 0.02 MHz, respectively, for an observation period of more than 10 hours. PACS 42.62.Fi; 42.55.Px; 32.30.-r     

Coherent spectroscopy of the 87RbFg=1→ Fe=0 closed transition

This paper has observed linewidth narrowing of dark states in rubidium cell by using the Hanle configuration. The reduction of the coherent resonance width under the transition of ^87Rb Fg = 1 → Fe = 0 is observed and the qualitative explanation about its mechanism is presented. Multiple subnatural width dips are obtained with a linearly polarized laser beam for the transitions of ^87Rb Fg = 1→Fe = 0, 1, 2. The feature of negative and positive slope, namely dispersionlike feature, is observed in the transmitted light.     

Selective excitation of the 62 D 3/2 state of the atomic thallium beam

The absorption of the tunable narrow-band laser radiation with λ = 276.9 nm at the 6² P _1/2 → 62 D _3/2 transition in the atomic thallium beam is experimentally studied. The isotopic selectivity and efficiency of the excitation of the 6² D _3/2 state is investigated. The splittings between the ²⁰³Tl and ²⁰⁵Tl isotopes were found to be Δv = 0.98 and 1.25 GHz for the transitions with the nuclear momenta F = 1 → F = 1, 2 and F = 0 → F = 1, respectively, which is sufficient for a relatively high isotopic selectivity of the 6² D _3/2 state excitation with the subsequent ionization for the laser separation of the thallium isotopes. The effects that lead to the broadening of the resonance and a decrease in the selectivity are analyzed. The main contribution is related to the field broadening by the laser radiation, which limits the mean laser power density.     

Observation of nonstationary effects in saturation spectroscopy

We have studied the nonstationary effects in saturated absorption spectroscopy of the ⁸⁷Rb D₂ line. Varying the size of the σ⁺ polarized pump laser beam, we observed saturated absorption spectra for the σ^± polarized probe beam. For equal polarizations of the pump and probe beams, we found that the resonance signal for the F_g = 1 → F_e = 2 line, and the crossover lines between F_g = 1 → F_e = 2 and F_g = 1 → F_e = 1 (and 0) lines increased to a greater extent than the others. This observation can be understood from the calculated time evolution of the populations of the ground-state sublevels by means of a rate equation model. We also compared experimental data for other conditions with the calculated results. We found good agreement between the calculated results and the data.     

Rearrangement of optical centers and stimulated radiation of Eu<Superscript>3+</Superscript> in polycrystalline huntite under optical and electron-beam excitation

Polycrystalline europium huntite EuAl₃(BO₃)₄ has been prepared by solid-phase synthesis. The spectral and kinetic characteristics of its luminescence under the excitation by a xenon lamp, single laser pulse, and electron beam have been studied. It has been established that the laser excitation of the polycrystalline samples in the ⁷ F ₀ →⁵ L ₆ transition of Eu³⁺ ions with the power density P ≥ 5 × 10⁷ W/cm² leads to the structure rearrangement of the optical centers, which is accompanied by an increase in the probability of the radiation transitions of the activator. The stimulated radiation of the main type of Eu³⁺ centers in the ⁵ D ₀→⁷ F ₁, ⁷ F ₂, and ⁷ F ₄ transitions has been obtained under the excitation by the electron beam with an energy of 200 keV and a duration of 2 ns.     

Saturated absorption spectroscopy: Elimination of crossover resonances with the use of a nanocell

It is demonstrated that the velocity-selective optical pumping/saturation resonances of the reduced absorption in a Rb vapor nanocell with thickness L = λ, 2λ, and 3λ (resonant wavelength λ = 780 nm) allow for the complete elimination of crossover (CO) resonances. We observe well-pronounced resonances corresponding to the F _g = 3 → F _e = 2, 3, and 4 hyperfine transitions of the ⁸⁵Rb D₂ line with line widths close to the natural width. A small CO resonance located midway between F _g = 3 → F _e = 3 and F _g = 3 → F _e = 4 transitions appears only for L ≥ 4λ. The D₂ line (λ = 852 nm) in a Cs nanocell exhibits a similar behavior. From the amplitude ratio of the CO and VSOP resonances, it is possible to determine the thickness of the column of alkali vapor in the range of 1–1000 μm. The absence of the CO resonances for nanocells with L ～ λ is attractive for the frequency reference application and for studying the transitions between the Zeeman sublevels in external magnetic fields.     

Use of sub-Doppler optical resonances for measurement of weak magnetic fields by means of extremely thin rubidium vapor cell

We study experimentally and theoretically D ₁ lines of ⁸⁵Rb and ⁸⁷Rb atoms and show that using atomic-velocity-selective optical resonances which are formed in the transmission spectrum of an atomic rubidium-filled submicron cell at single pass of linearly polarized laser radiation, it is possible to measure weak magnetic fields beginning with 5 G. Having in mind the results obtained earlier with use of also submicron cell with ⁸⁷Rb (D ₁ line) and circularly polarized laser radiation, the entire range of measurable magnetic fields (both homogeneous and inhomogeneous) becomes 5–5000 G.     

Sub-natural linewidth resonances in coherently-driven double Λ system

We investigate theoretically the pump-probe spectroscopy of coherently-driven four-level Λ system with two closely spaced excited common levels, thereby forming a double Λ system. Using the master equation approach, analytical results are obtained for the absorption spectrum of a weak probe in the presence of a strong pump. The model is applied to the double Λ system 5² S _1/2 F = 1, 2 → 5² P _3/2 F′ = 1,2 of ⁸⁷Rb atom. It is shown that the absorption spectrum consists of a triplet, of which one resonance is of sub-natural linewidth depending on the atom-field interaction parameters. The effect of Doppler broadening on the absorption spectrum is also investigated.     

Polarized single top quark production in eγ collision and anomalous Wtb couplings

We investigate the potential of eγ collisions to probe anomalous Wtb couplings via the polarized single top quark production process e⁺γ→tb̄ν_ē. We find 95% confidence level limits on the anomalous coupling parameters F_2L and F_2R with an integrated luminosity of 500 fb^-1 and , 1 and 1.5 TeV energies. The effects of top quark spin polarization on the anomalous Wtb couplings are discussed. It is shown that polarization leads to a considerable improvement in the sensitivity limits. PACS 14.65.Ha; 13.88.+e     

Doppler spectroscopy of arbitrarily polarized light in rubidium

We present an experimental and theoretical study of the transmission of an arbitrarily polarized laser beam for a Doppler broadened rubidium vapor cell. As the polarization of the probe beam was varied from linear to circular, the transmission for the transitions F_g = 3 → F_e = 2, 3, 4 of the D₂ line of ⁸⁵Rb atoms was measured and compared with calculated results. In the calculation, the time-dependent absorption coefficient, calculated numerically from the density-matrix equation, was averaged over the velocity distribution and various transit time crossing the laser beam. The final transmission was obtained by considering the Gaussian profile of the laser beam. We found good agreement between experimental and calculated results.     

Search for solar axions produced in the p + d → <Superscript>3</Superscript>He + A reaction

A search for the axioelectric absorption of 5.5-MeV solar axions produced in the p + d → ³He + γ (5.5 MeV) reaction was performed with two BGO detectors placed inside a low-background setup. Constraints on the axion-electron coupling constant were obtained for axions with masses in the (0.1–1.0)-MeV range: g _Ae ≤ (1.8–9.0) × 10⁻⁷. The solar positron flux from A → e⁻ + e⁺ decay was determined for axions with masses m _A > 2m _e. Using the existing experimental data on the interplanetary positron flux, a new constraint on the axion-electron coupling constant for axions with masses in the (1.2–5.4)-MeV range was obtained: g _Ae ≤ (1–5) × 10⁻¹⁷.     

Adaptive Sub-sampling for Parametric Estimation of Gaussian Diffusions

We consider a Gaussian diffusion X _t (Ornstein-Uhlenbeck process) with drift coefficient γ and diffusion coefficient σ ², and an approximating process Y^e_tY^{\varepsilon}_{t} converging to X _t in L ₂ as ε→0. We study estimators [^(g)]_e\hat{\gamma}_{\varepsilon}, [^(s)]²_e\hat{\sigma}^{2}_{\varepsilon} which are asymptotically equivalent to the Maximum likelihood estimators of γ and σ ², respectively. We assume that the estimators are based on the available N=N(ε) observations extracted by sub-sampling only from the approximating process Y^e_tY^{\varepsilon}_{t} with time step Δ=Δ(ε). We characterize all such adaptive sub-sampling schemes for which [^(g)]_e\hat{\gamma}_{\varepsilon}, [^(s)]²_e\hat{\sigma}^{2}_{\varepsilon} are consistent and asymptotically efficient estimators of γ and σ ² as ε→0. The favorable adaptive sub-sampling schemes are identified by the conditions ε→0, Δ→0, (Δ/ε)→∞, and NΔ→∞, which implies that we sample from the process Y^e_tY^{\varepsilon}_{t} with a vanishing but coarse time step Δ(ε)≫ε. This study highlights the necessity to sub-sample at adequate rates when the observations are not generated by the underlying stochastic model whose parameters are being estimated. The adequate sub-sampling rates we identify seem to retain their validity in much wider contexts such as the additive triad application we briefly outline.     

Experimental investigation of evaporative cooling mixture of bosonic 87Rb and fermionic 40K atoms with microwave and radio frequency radiation

We investigate sympathetic cooling fermions ⁴⁰K by evaporatively cooling bosonic ⁸⁷Rb atoms in a magnetic trap with microwave and radio frequency induced evaporations in detail. The mixture of bosonic and fermionic atoms is prepared in their polarized spin states |F=9/2, m_F=9/2> for ⁴⁰K and |F=2, m_F=2> for ⁸⁷Rb, which is trapped in Quadrupole--Ioffe--Configuration trap. Comparing microwave with radio frequency evaporatively cooling bosonic ⁸⁷Rb atoms with sympathetically cooling Fermi gas ⁴⁰K, we find that the presence of rubidium atoms in the |2,1> Zeeman states, which are generated in the evaporative process, gives rise to a significant loss of ⁴⁰K due to inelastic collisions. Thus, the rubidium atoms populated in the |2, 1> Zeeman states should be removed in order to effectively perform sympathetically cooling ⁴⁰K with the evaporatively cooled ⁸⁷Rb atoms.     

Synchrotron and annihilation channels for axion production in an external electromagnetic field

We consider axion formation processes in the synchrotron (e ⁻→e ⁻ a) and annihilation (e ⁻ e ⁺→a) channels in a constant crossed field F _μν F^μν=Fμν*F ^μν =0, which approximates constant fields of other configurations in the ultrarelativistic asymptotic limit. The probability and intensity of axion emission are obtained, and we analyze the energy and field asymptotics. A comparison with the characteristic neutrino channel yields the constraints on the axion mass and the energy scale for Peccei-Quinn symmetry breaking. Possible astrophysical applications are discussed. Zh. éksp. Teor. Fiz. 112, 25–31 (July 1997)     

Atom in an elliptically polarized resonance field: Exact stationary solution

An analytical method is developed for finding the exact stationary solution for the density matrix of atoms in a monochromatic resonance field of arbitrary ellipticity and intensity. A solution for the transitions F _g=F → F _e=F+1 (F _g and F _e are the angular momenta of the ground and excited states) is obtained in an analytical invariant form. The properties of this solution are investigated. Pis'ma Zh. éksp. Teor. Fiz. 64, No. 1, 8–12 (10 July 1996)     

Polarized angular distributions in the decays of the ψ’ charmonium state directly produced in unpolarized proton–antiproton collisions

Using the helicity formulism, we calculate the combined angular distribution function of the polarized gamma photons and electron in the cascade process pp̄→ψ’→χ_J+γ₁→ψ+γ₂+γ₁→e⁺+e^-+γ₂+γ₁ (J=0,1,2), when p̄ and p are unpolarized. We also present the partially integrated angular distribution functions in different cases. Our results show that by measuring the two-particle angular distribution of γ₁ and γ₂ and that of γ₂ and e^- with the polarization of either one of the two particles, one can determine the relative magnitudes as well as the relative phases of the helicity amplitudes in the radiative decay processes ψ’→χ_J+γ₁ and χ_J→ψ+γ₂. PACS  11.80.Cr; 13.20.Fc; 13.60.Le; 14.40.Gx