Raman Sideband Research Articles

Raman sideband cooling in the presence of multiple decay channels

We have investigated the efficiency of pulsed Raman sideband cooling in the presence of multiple decay and excitation channels. By applying sum rules we identify parameter regimes in which multiple scattering of photons can be described by an effective wave vector. Using this method we determine the rate of heating caused by optical pumping inside and outside the Lamb–Dicke regime. On this basis we discuss also the efficiency of a recently proposed scheme for ground-state cooling outside the Lamb–Dicke regime [Europhys. Lett. 39 (1997) 13].

Sideband generation using strongly driven raman coherence in solid hydrogen

Parametric Raman sideband generation is investigated using strongly driven Raman coherence in solid hydrogen. We show that the Raman coherence prepared with two coaxial single-mode lasers beats with multimode laser radiation with very broad bandwidth and efficiently replicates the broadband nature to the Raman sidebands without the restriction of phase matching. We demonstrate that this efficient replication occurs mainly on the negative side of Raman detuning, where the medium adiabatically follows the antiphased state.

3D raman sideband cooling of cesium atoms at high density

We laser cool 5x10(7) Cs atoms to a spin-polarized phase space density of 1/30, the highest ever obtained by laser cooling. It is achieved by compression and polarization gradient cooling in a 3D far-off-resonant optical lattice, followed by 3D Raman sideband cooling optimized at a density of 1.5x10(12) atoms/cm(3), and adiabatic release. In the lattice, 23% of the sites are occupied, 95% of the atoms are in the lowest energy magnetic sublevel, and 37% are in the lowest 3D vibrational state.

Stimulated Raman scattering with slow light

We study the propagation dynamics of weak Raman sideband fields in a far-off-resonance Raman medium driven by a strong coupling field. We show that the interaction of the system with the strong field, under the conditions of high density, narrow Raman-transition width, and small two-photon detuning, results ina slow group velocity and a substantial enhancement of the injected anti-Stokes sideband field as well as an efficient generation of a Stokes sideband field. We find that the effective group velocity is the same for the two weak fields and is proportional to the field frequency difference instead of the frequency of the corresponding field. We also discuss the condition for exponential growth of the two sideband fields in the medium. We perform numerical calculations for solid hydrogen, a realistic system where the requirements for high density and small Raman width can be met. We demonstrate that the group velocity can be slowed down by several orders, and that the slow light plays a key role for the stimulated Raman scattering process in solid hydrogen.PACS Nos.: 42.50Gy, 42.50Hz, 42.65Ky, 42.79Nv

Beyond optical molasses: 3D raman sideband cooling of atomic cesium to high phase-space density

We demonstrate a simple, general purpose method to cool neutral atoms. A sample containing 3x10(8) cesium atoms prepared in a magneto-optical trap is cooled and simultaneously spin polarized in 10 ms at a density of 1.1x10(11) cm (-3) to a phase space density nlambda(3)(dB) = 1/500, which is almost 3 orders of magnitude higher than attainable in free space with optical molasses. The technique is based on 3D degenerate Raman sideband cooling in optical lattices and remains efficient even at densities where the mean lattice site occupation is close to unity.

Raman motional displacements of a trapped ion in the strong excitation regime

We consider the first-sideband Raman excitations of a trapped ion in the strong Raman coupling regime on the basis of the splitting approximation. It is demonstrated that not only weak but strong Raman excitations can be used to displace the motional ground state to some well-localized motional states under appropriate conditions. Nonlinear and nonresonant effects are taken into account for the Raman sideband transitions. The condition and limitation for the Raman vibrational excitations to be used for preparing Schr\"odinger cat motional states are analyzed. Quantum interference between the displaced motional states is discussed.

Nonlinear Raman vibrational excitation of a trapped ion

Raman sideband excitations driven by counterpropagating Raman beams are analyzed for the trapped ion under the localization conditions in and beyond the Lamb-Dicke regime. Multiquantum vibrational couplings are demonstrated to produce significant effects on the Raman sideband transitions and the relevant Raman excitations of the trapped ion beyond the Lamb-Dicke regime. The quantum features of the vibrational states attained by exciting the motional ground state are closely associated with the nonlinear vibronic couplings, Raman excitation, and localization conditions. Quantum entanglement and quantum interference are discussed for the trapped ion under various Raman excitation and localization conditions. The results are compared with the recent experiments. Further experimental attempts are proposed to use the single trapped ${}^{25}{\mathrm{Mg}}^{+}$ ion in a linear ion trap.

Degenerate Raman Sideband Cooling of Trapped Cesium Atoms at Very High Atomic Densities

We trap ${10}^{7}$ cesium atoms in a far red detuned 1D optical lattice. With degenerate Raman sideband cooling we achieve a vibrational ground state population of 80% for the steep trapping direction. Collisional coupling enables us to cool the spin-polarized gas in 3D without loss of atoms to a peak phase space density of $1/180$ at a mean temperature of $2.8\ensuremath{\mu}\mathrm{K}$ and a density of $1.4\ifmmode\times\else\texttimes\fi{}{10}^{13}{\mathrm{cm}}^{\ensuremath{-}3}$.

Increased radiative lifetime of rare earth-doped zinc oxyhalide tellurite glasses

We have investigated the structural and optical properties of rare earth-doped zinc tellurite glasses modified by the substitution of ZnF2. Raman and phonon sideband spectroscopies were employed to characterize changes in the glass structure as well as to probe vibrational behavior in the immediate vicinity of the rare earth ion. These measurements are combined with photoluminescence and optical absorption to monitor the effect of halide substitution upon the optical behavior of the rare earth dopant. A substantial increase in the intrinsic radiative lifetime of Nd3+ is observed with increasing halide concentration.

Vibron–phonon excitations in the molecular crystals N2, O2, and CO by Fourier transform infrared and Raman studies

The influence of temperature on the vibron–phonon combination band in the Raman and infrared (ir) spectra of the N2 and O2 molecular crystals supports the possibility of an assignment of the main features in the sideband to strong contributions from translational and librational phonons in points of high symmetry in the reciprocal lattices. The temperature behavior in Raman and ir sideband spectra in α-N2 is attributed to distinct anharmonicities in the isotropic and anisotropic parts of the potential and to different coupling mechanisms, resulting in a librational and translational weighted one-phonon density of states (DOS). In contrast, such an interpretation is not feasible for the poorly structured CO sideband, although the crystal structures of CO and N2 are nearly identical. The difference is attributed to strong anharmonicities and the presence of a weak dipole moment in the former, which introduces strong lattice mode coupling. Crossing the α–β phase transition has marked effects on the sidebands (shape, intensity) in both N2 and O2 crystals, which reflects the orientational disorder in the β phase of the former and the importance of the change in magnetic interactions in the latter. For both molecular crystals, the vibron–phonon coupling to the electromagnetic field is stronger in the ir than in the Raman spectra and seems predominantly due to electrical anharmonicities.

A p r i o r i rates of phonon-assisted v–v transfers among CO and N2 molecules in N2 matrices

The method of computing matrix shifts, splittings, and sideband intensities of the vibrational fundamental bands in solid N2 and CO has been extended to the calculation of resonant and off-resonant v–v transfer rates. The contribution of mechanical anharmonicity, i.e., vibron–phonon coupling through third- and higher-order terms in the potential, is found to be negligible for phonon-assisted transfer rates, similar to the situation in ir and Raman sideband intensities. Electrical anharmonicity, i.e., the modulation of vibron resonance energies by phonon-type motions, produces off-resonant v–v rates which are larger than those due to mechanical anharmonicity by two orders of magnitude. Analytical expressions have been derived for the quantitative determination of rates based on static multipole–multipole interactions, and contributions by repulsive exchange forces have been calculated numerically. The calculated rates are consistent with observations in a system of CO diluted in N2 and they explain the observed temperature behavior of endothermic v–v processes in pure solid N2 where two and more phonons are involved. It is found that molecular librations dominate over translational motions in all of these phonon-assisted rates, even in the repulsive contributions.