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Nonlinear Faraday rotation with counter-propagating light beams was investigated in a rubidium vapor cell. Observations across all hyperfine and crossover resonances of the D-2 line of Rb-87 atoms were made. Additionally, rotation spectra as a function of pump and probe intensity, pump polarization and external magnetic field strength were studied. The investigations were performed in a regime where the pump beam power was sufficiently low relative to the probe power to avoid polarization rotation due to pump-induced anisotropy. Our results are analyzed in the context of Bennett structures and coherent optical processes. (c) 2007 Elsevier B.V. All rights reserved.

Observation of transient effects in electromagnetically induced transparency (EIT) is reported in ${\mathrm{Rb}}^{85}$ cooled in a magneto-optical trap. The transmission of a weak probe beam in resonance with the ${5S}_{1/2}(F=3)$ to ${5P}_{3/2}(F=3)$ hyperfine transition increased transiently when a relatively strong coupling field in resonance with the ${5S}_{1/2}(F=2)$ to ${5P}_{3/2}(F=3)$ hyperfine transition was switched on rapidly using a Pockels cell. The probe transient showed an initial Rabi half-cycle overshoot before settling down to steady-state EIT. The results agreed well with computations using a three-state model of the \ensuremath{\Lambda} system. The computations also suggest that transient gain should be observed with coupling field power only four times larger than that presently available to us.

We report experiments demonstrating the effects of optical pumping, coherent population trapping and light polarisation on electromagnetically induced transparency in simple Λ-type configurations of rubidium 87 where the relevant coherences are within the three Zeeman substates of the F=1 component of the 5S1/2 ground level. Inversionless gain is also demonstrated. The sample is cooled to below 1 mK in a magneto-optic trap operating without repumping light to give a working population of F=1 ground state atoms. The experimental results are compared with master equation computations of a closed seven-substate-model representing the ground level (F=1) and the excited levels F′=0 and F′=1.

The electric field polarization structure of three-dimensional monochromatic electromagnetic fields is investigated, with particular reference to the three-dimensional standing waves that are commonly used in laser cooling. Two parameters are introduced for describing the polarization at a field point, one of which is a generalization of the Stokes ellipticity parameter while the other describes the rotation of linear polarization (or the polarization ellipse) for small displacements. The two parameters are shown to be simply related to the density and flux of intrinsic angular momentum (spin) in the field. Additional parameters are introduced to provide measures of the polarization gradients on straight line trajectories in three-dimensional standing waves and the implications for laser cooling are discussed.

We have observed electromagnetically induced transparency (EIT) in laser-cooled rubidium in a magneto-optical trap (MOT). Λ-type configurations of hyperfine levels of the D2 line were studied, as well as a system utilising degenerate Zeeman sublevels of the ground state. V-type signals were also seen. The perturbing effects of the MOT were found to be small and the results agree well with standard EIT theory for homogeneously-broadened samples.

We outline the theory of a practical Bragg scattering technique for studying the long-range spatial order of atoms localized in one-dimensional optical lattices and we demonstrate the technique using and F = 1 → 1 transitions with lin ⊤ lin laser cooling fields. The latter transition gives a dark optical lattice. We show that the scattering by a spin grating, which may also be present, can be completely or partially filtered out by varying the polarizations of the cooling fields while holding the polarization of the probe and the detector analyser fixed. This allows the fraction of atoms that are localized to be measured. The probe field is treated as a pulse and so the technique also allows time-resolved details of the spatial structure to be studied.

The semiclassical light force on a free atom is derived as the reaction on the atom of momentum loss from and exchange between plane wave modes of a classical light field. This approach leads directly to an expression for the force that is computationally convenient for multidimensional laser field configurations under conditions where a two-level model of the atoms is appropriate, and provides insight into the origin of the light force in terms of loss, gain and exchange of mode momenta.

Three pulse echoes are used to measure the collisional destruction of Zeeman coherences in caesium (6S1/2−7P1/2) perturbed by low pressures of helium, argon and xenon. Anomalously large collision r...

Interest in lossless nonlinearities has focussed on the the dispersive properties of $\Lambda $ systems under conditions of electromagnetically induced transparency (EIT). We generalize the lambda system by introducing further degenerate states to realize a `Chain $ \Lambda $' atom where multiple coupling of the probe field significantly enhances the intensity dependent dispersion without compromising the EIT condition., Comment: 6 pages, 7 figures, revtex 4, Two errors corrected (|D_0^{(7)}> and R^{(7)}, Replaced with version accepted in Phys. Rev. A

Many approaches to quantum control explicitly assume idealized cases. Starting with an idealized control scheme derived using Lie group decompositions, we employ computer models to simulate the effect of spontaneous emission that occurs in a realistic system, and attempt to optimize the performance of the control scheme. For illustration. we use a four-state Rubidium atom with transitions as indicated in Fig. 1, where ω n are the frequencies and f n are the absorption oscillator strengths of the transitions. Assuming that the atom is initially in the ground state |1〉 = |5S 1/2〈, our aim is to maximise the population inversion between states |1〉 and |4〉 = |6P 3/2 by applying control pulses derived from resonant, intense laser beams. For simplicity, we assume that the pulse envelopes of our lasers are Gaussian and off-resonant effects can be neglected.

Spectra illustrating the doubly driven N system are presented with accompanying dressed state analysis. The spectra show a three-photon absorption peak in addition to the normal EIT profile, due to the second coupling field.

This work studies the lossless intensity-dependent dispersion in coherently prepared multi-state atoms using electromagnetically induced transparency (EIT). This study also describes the chain /spl Lambda/ atoms, identifies realistic conditions for observing chain /spl Lambda/ atoms, presents extended results where propagation effects are taken into account and explores the prospects for using such atoms in novel quantum devices.

We have observed clear Rabi oscillations of a weak probe in a strongly driven three-level lambda system in laser-cooled rubidium for the first time. When the coupling field is non-adiabatically switched on using a Pockels cell, transient probe gain without population inversion is obtained in the presence of uncoupled absorptions. Our results are supported by three-state computations., Comment: 4 pages, 4 figures, experimental results

Observations of a doubly driven V system probed to a fourth level in an N configuration are reported. A dressed state analysis is also presented. The expected three-peak spectrum is explored in a cold rubidium sample in a magneto-optic trap. Good agreement is found between the dressed state theory and the experimental spectra once light shifts and uncoupled absorptions in the rubidium system are taken into account., Comment: 8 pages, 8 figures, Replaced with version scheduled to appear in 1 July 2001 issue of Physical Review A

This paper presents a wide-ranging theoretical and experimental study of non-adiabatic transient phenomena in a $\Lambda $ EIT system when a strong coupling field is rapidly switched on or off. The theoretical treatment uses a Laplace transform approach to solve the time-dependent density matrix equation. The experiments are carried out in a Rb$^{87}$ MOT. The results show transient probe gain in parameter regions not previously studied, and provide insight into the transition dynamics between bare and dressed states., Comment: 19 Pages, 9 Figures, 1 in colour. RevTex 4.0 Submitted to Physical Review A

We show that for appropriate choices of parameters it is possible to achieve photon blockade in idealised one, two and three atom systems. We also include realistic parameter ranges for rubidium as the atomic species. Our results circumvent the doubts cast by recent discussion in the literature (Grangier et al Phys. Rev Lett. 81, 2833 (1998), Imamoglu et al Phys. Rev. Lett. 81, 2836 (1998)) on the possibility of photon blockade in multi-atom systems., 8 page, revtex, 7 figures, gif. Submitted to Journal of Optics B: Quantum and Semiclassical Optics

Polarization gradients in light fields formed at the intersection of three orthogonal pairs of counterpropagating waves of the same frequency are studied numerically. The aim is to gain insight into sub‐doppler cooling in 3‐dimensional optical molasses.

The collisional relaxation of photon echoes generated on the 6S built1 2 - 7P built3 2 (455 nm) transition in caesium has been observed and measured as a function of perturber pressure. Values for the collision cross-sections have been obtained using helium, neon, argon and krypton as perturbers. There is good agreement between these results and those obtained from high resolution measurements of pressure-broadened line profiles. The echoes were observed using the polarization rotation technique and all the measurements were made at perturber pressures below 0.5 torr.

The mechanisms behind the amplification of light by stimulated emission are investigated using a semiclassical approach. The theory is developed in the plane wave mode picture so as to follow closely the correspondence with the usual quantized field treatment. It is shown that the interference between stimulating and stimulated fields is an essential process for producing the well-known first-order effects, and that interference between stimulated emission fields from different atoms in the sample determines the spatial distribution of the amplification when this is measured locally using a light detector without mode discrimination.

The possibility of a class of optical echo-producing mechanisms is suggested that does not invoke the phase-reversal action of the second pulse. The mechanisms act selectively on the radiating atomic dipole moments, or on their radiation fields, with a periodic dependence on Δτ, where Δ is the angular frequency of the radiator relative to the central angular frequency of the distribution and τ the interpulse time. In the new formulation, the customary expression for the field radiated by an atomic dipole following a two-pulse excitation sequence is multiplied by a factor periodic in Δτ. It is shown that a sequence of echo pulses is predicted when the average over the radiators is calculated. One such mechanism is proposed: the selective absorption or amplification of the dephased free-induction decay field as they propagate through the sample.

Measurements are presented of the collisional relaxation of two-pulse echoes on the 455 nm and 459 nm D-lines of atomic caesium perturbed by low pressures of He, Ar and Xe using the echo-polarisation rotation technique, with interpulse times up to approximately 200 ns. The line broadening constants are measured to about 3% and show significant discrepancies with line profile measurements. For τ ⩾ 100ns there is evidence for the diffractive velocity-changing aspects of the collisions. The mean collisional velocity changes and the cross-sections for diffractive velocity-changing collisions are estimated from the data. The results are found to be insensitive to variations of axial magnetic fields and optical densities.

It is shown that phase-interrupting collisions occurring during the period of the second excitation pulse in a photon echo experiment do not in general destroy the coherent dipole moments of the perturbed atoms, however hard the collision may be. An effective collision rate for this period is determined; it can be larger or smaller than the actual collision rate, depending on the pulse area. The application to measurements of collisional cross-sections is discussed.

In a recent paper Mandel and Wolf use a two-parameter susceptibility function to derive an expression for the spectral density of the induced polarisation in a linear fluctuating medium. Their treatment is restricted to time-stationary fields and media. This paper presents (i) a generalisation of their treatment to include the case of locally stationary fields which is of interest in the study of resonance fluorescence spectroscopy; (ii) a demonstration of the way in which the spectral density of the fluctuations and the atomic spectral response function are combined in the two-parameter description of the susceptibility of an atomic vapour.

We report tri-level echo measurements of collision cross-sections and broadening constants for the electric-dipole-forbidden fine-structure transition in caesium (7p 1 2 - 7P 3 2 ) perturbed by low pressures (

Summary form only given. Many studies have been made of electromagnetically induced transparency (EIT) and probe gain under steady-state conditions. We have carried out experimental studies of transient effects in rubidium lambda systems in the non-adiabatic regime where the coupling field is rapidly switched on using a Pockels cell in a time that is short compared with transient time scales. Our preliminary work has confirmed predictions that the steady-state EIT is approached through damped oscillations characterised by the coupling field Rabi frequency /spl Omega//sub c/ and the spontaneous decay rate /spl Gamma/. We report results of our recent investigations into the effects of strong coupling fields conducted in several different lambda schemes in the rubidium 5S/sub 1/2/-5P/sub 3/2/ hyperfine levels in a magnetooptical trap. We also studied the effects of the initial conditions of population and optical coherence, probe absorption on uncoupled Zeeman transitions, and incoherent pumping.

Nonlinear Faraday rotation (NFR) was studied for 87Rb atomic D2 Fg = 2-Ft =1,2,3 transitions with crossed polarizers, with varying longitudinal magnetic field strength S = 0-10 G. The experiment was realized in counter-propagating beam Doppler-free geometry.