C. R. Stroud

Coherent trapping of atomic populations

It is often desirable in laser spectroscopy and isotope separation to extract as much as possible of an atomic or molecular population that is distributed among a number of ground-state sublevels and low-lying metastable levels. We describe a form of coherent trapping that occurs when multiple resonant laser beams are used to couple the various ground states to a common upper level. This effect prevents the extraction of the entire population. We then study the effect with two dye lasers and an atomic beam and suggest possible ways to maximize the pumping efficiency.

Observation of the resonant Stark effect at optical frequencies

The spectrum of resonantly scattered light at right angles to a sodium atomic beam is reported. The light source was a cw dye laser tuned to resonance with a hyperfine component of the Dz line, and incident at right angles to the atomic beam. The spectrum, with the Stark effect sidebands, was recorded as a function of both the laser intensity and its detuning from resonance. The overall resolution is better than 20 MHz.

Steady-state quantum interference in resonance fluorescence

It is shown that when a monochromatic laser couples a single atomic ground level to two closely spaced excited levels the system can be driven into a state in which quantum interference prevents any fluorescence from the excited levels, regardless of the intensity of the exciting field. This steady-state interference occurs only at a particular excitation frequency which depends on the separation of the excited states and the relative size of the two transition dipole matrix elements. The results are derived from the density matrix equations of motion. It is shown that a correct description of the effect requires the inclusion of generalised Einstein A coefficients which are usually neglected in phenomenological damping theories. A dressed-state analysis is introduced to simplify the generalisation to atoms having more complex manifolds of excited states. Analogous interferences in multiphoton absorption and ionisation are also discussed briefly.

Observation of a spectral hole due to population oscillations in a homogeneously broadened optical absorption line

Abstract We have observed a dip in the absorption profile of the homogeneously broadened green absorption band of ruby for frequencies near that of a saturating, cw laser beam. The shape and depth of the hole thus produced have been measured using weak amplitude modulation sidebands as a probe, and are found to be in good agreement with theoretical predictions. These predictions are based on a model that ascribes the origin of the hole to the periodic modulation of the ground state population at the beat frequency between the pump and probe beams. The theory includes the effect of pump depletion. Holes as narrow as 37 Hz (HWHM) have been observed.

Autler-Townes effect in double optical resonance

Abstract Two frequency stabilized dye lasers and a sodium atomic beam are used to study the Autler-Townes effect in the aligned 3S 1 2 , F = 2, M F = 2 → 3P 3 2 , F = 3, MF = 3, → 4D 5 2 , F = 4, MF = 4 states. This system is to a very good approximation an isolated three-level atom. The Autler-Townes doublet splittings are measured as a function of the intensities of the two lasers and their detunings from resonance. The experimental results are in good agreement with theory.

Classical and quantum-mechanical dynamics of a quasiclassical state of the hydrogen atom.

We explore the classical limit of the hydrogen atom by constructing a minimum-uncertainty wave packet that travels along a Kepler orbit. The dynamics of the wave packet display both classical and quantum-mechanical properties. Over a limited period of time, during which the dynamics of the wave packet may be considered linear, the motion of the wave packet can be described by classical equations of motion. After this time, the quantum dynamics, whose most prominent features are decays and revivals of the wave packet, becomes dominant. We discuss decays and revivals of the wave packet in detail.

Spatiotemporal shaping of half-cycle terahertz pulses by diffraction through conductive apertures of finite thickness

We demonstrate a simple quasi-optical technique for spatiotemporal shaping of half-cycle terahertz-radiation pulses. We show, both experimentally and theoretically, that properly polarized half-cycle pulses can be modulated temporally by diffraction through a conductive aperture of finite thickness. We use the finite-difference time-domain method to solve Maxwell’s equations for such a geometry and show that it can explain all the experimentally observed features. In the case of thick aperture, a planar waveguide model can also be used to describe the propagation of the pulse through the aperture, with excellent agreement with the experimental results.

Room temperature single-photon Source:Single-dye molecule fluorescence in Liquid Crystal host

We report on new approaches toward an implementation of an efficient, room temperature, deterministically polarized, single-photon source (SPS) on demand-a key hardware element for quantum information and quantum communication. Operation of a room temperature SPS is demonstrated via photon antibunching in the fluorescence from single terrylene-dye molecules embedded in a cholesteric liquid crystal host. Using oxygen-depleted liquid crystal hosts, dye-bleaching was avoided over the course of more than 1 h of continuous 532-nm excitation. Liquid crystal hosts (including liquid crystal oligomers/polymers) permit further increase of the efficiency of the source: 1) by aligning the dye molecules along a direction preferable for maximum excitation efficiency; 2) by tuning a one-dimensional (1-D) photonic-band-gap microcavity of planar-aligned cholesteric (chiral nematic) liquid crystal layer to the dye fluorescence band.

Resonance in quantum dot fluorescence in a photonic bandgap liquid crystal host

Microcavity resonance is demonstrated in nanocrystal quantum dot fluorescence in a one-dimensional (1D) chiral photonic bandgap cholesteric-liquid crystal host under cw excitation. The resonance demonstrates coupling between quantum dot fluorescence and the cholesteric microcavity. Observed at a band edge of a photonic stop band, this resonance has circular polarization due to microcavity chirality with 4.9 times intensity enhancement in comparison with polarization of the opposite handedness. The circular-polarization dissymmetry factor g(e) of this resonance is ~1.3. We also demonstrate photon antibunching of a single quantum dot in a similar glassy cholesteric microcavity. These results are important in cholesteric-laser research, in which so far only dyes were used, as well as for room-temperature single-photon source applications.

SELF-INDUCED TRANSPARENCY IN SELF-CHIRPED MEDIA

Abstract Resonant absorbing media having many atoms within a cubic resonance wavelength can exhibit large frequency chirps in pulse propagation due to dipole-dipole interactions among the atoms. Analytic solutions are obtained for invariant pulse propagation in such a medium consisting of interacting two-level atoms. Departures from the McCall-Hahn results include nonhyperbolic secant pulse shapes and different than 2π-area pulses. In addition, the excitation of the medium is comparatively suppressed for the same group velocity. The results are interpreted to suggest new experiments.