Collective Atomic Recoil Motion Research Articles

Saturation of superradiant light scattering from an atomic grating with a large number of atoms

Superradiance has drawn increasing interest, motivated by the development of quantum technology. In general, a large number of atoms are favored for inducing a strong superradiance. However, our analytical and numerical calculations of light scattering from an atomic grating longitudinally pumped by a laser show that when the atom number is small, superradiant light scattering (SLS) is induced, that is, the reflected light intensity is proportional to the square of the atom number, whereas the SLS is saturated with the increase in the atom number. In our calculation, using the coupled-wave theory, we treat the atomic grating as a dynamical photonic crystal and find rich time-dependent optical properties due to collective atomic recoil motion, which is available within research under current experimental condition. Thus, our paper could also spark an investigation of the optical features of tunable photonic crystals in the time domain.

Light-wave mixing and scattering with quantum gases

We show that optical processes originating from elementary excitations with dominant collective atomic recoil motion in a quantum gas can profoundly change many nonlinear optical processes routinely observed in a normal gas. Not only multi-photon wave mixing processes all become stimulated Raman or hyper-Raman in nature but the usual forward wave-mixing process, which is the most efficient process in normal gases, is strongly reduced by the condensate structure factor. On the other hand, in the backward direction the Bogoliubov dispersion automatically compensates the optical- wave phase mismatch, resulting in efficient backward light field generation that usually is not supported in normal gases.

Optical self-focusing effect in coherent light scattering with condensates

We present a theoretical investigation of optical self-focusing effects in light scattering with condensates. Using long (>200 µs), red-detuned pulses we show numerically that a non-negligible self-focusing effect is present that causes rapid optical beam width reduction as the scattered field propagates through a medium with an inhomogeneous density distribution. The rapid growth of the scattered field intensity and significant local density feedback positively to further enhance the wave generation process and condensate compression, leading to highly efficient collective atomic recoil motion.

Highly efficient counter-propagation-beamsnarrow-band ultraviolet frequency conversion in a quantum gas

We show that highly efficient ultraviolet frequency up conversion can be established in a single-component quantum gas in the counter-propagating weak pump beam geometry where no frequency up conversion can occur in a normal gas. We also show that all light-wave mixing and scattering processes in quantum gases originating from elementary excitations characterized by efficient collective atomic recoil motion are stimulated Raman/hyper-Raman in nature.

Light-Wave Mixing and Scattering with Quantum Gases

We present a semiclassical theoretical framework on light-wave mixing and scattering with single-component quantum gases. We show that these optical processes originating from elementary excitations with dominant collective atomic recoil motion are stimulated Raman or hyper-Raman in nature. In the forward direction the wave-mixing process, which is the most efficient process in normal gases, is strongly reduced by the condensate structure factor even though the Bogoliubov dispersion relation automatically compensates the optical-wave phase mismatch. In the backward direction, however, the free-particle-like condensate structure factor and Bogoliubov dispersion result in highly efficient light-wave mixing and collective atomic recoil motion that are enhanced by a stimulated hyper-Raman gain and a very narrow two-photon motional state resonance.

Observation of Collective Atomic Recoil Motion in a Degenerate Fermion Gas

We demonstrate collective atomic recoil motion with a dilute, ultracold, degenerate fermion gas in a single spin state. By utilizing an adiabatically decompressed magnetic trap with an aspect ratio different from that of the initial trap, a momentum-squeezed fermion cloud is achieved. With a single pump pulse of the proper polarization, we observe, for the first time, multiple wave-mixing processes that result in distinct collective atomic recoil motion modes in a degenerate fermion cloud. Contrary to the case with Bose condensates, no pump-laser detuning asymmetry is present.

Observation of a Red-Blue Detuning Asymmetry in Matter-Wave Superradiance

We report the first experimental observation of strong suppression of matter-wave superradiance using blue-detuned pump light and demonstrate a pump-laser detuning asymmetry in the collective atomic recoil motion. In contrast to all previous theoretical frameworks, which predict that the process should be symmetric with respect to the sign of the detuning of the pump laser from the one-photon resonance, we find that for condensates the symmetry is broken. With high condensate densities and red-detuned pump light the distinctive multiorder, matter-wave scattering pattern is clearly visible, whereas with blue-detuned pump light superradiance is strongly suppressed. However, in the limit of a dilute atomic gas symmetry is restored.

Collective atomic recoil motion in short-pulse matter-wave superradiance

We show that a Bragg resonance is substantially incapacitated in short-pulse, matter-wave superradiant scatterings and both positive- and negative-order scatterings contribute equally. We further show that propagation gain is small and scattering events primarily occur at the ends of the condensate where the generated field has maximum strength. This explains the apparent ``asymmetry'' in the scattered components with respect to the condensate center. In contrast to long-pulse excitation, we prove that the generated field travels near the speed of light in vacuum and show that this has a significant impact on scattering. Finally, we show that when the excitation rate increases, the front-edge steepening and forward shifting of the peak of the generated field are due to depletion of the condensate.

Self-organization effects and light amplification of collective atomic recoil motion in a harmonic trap

Self-organization effects related to light amplification in the collective atomic recoil laser system with the driven atoms confined in a harmonic trap are investigated further. In the dispersive parametric region, our study reveals that the spontaneously formed structures in the phase space contributes an important role to the light amplification of the probe field under the atomic motion being modified by the trap.

Light amplification through collective atomic recoil motion modified by a harmonic potential

Light amplification in a collective atomic recoil laser with an active medium confined in an external harmonic trap is investigated. Our study confirms the possibility of a great promotion of the lasing efficiency due to the collective atomic recoil motion being modified by the trapping potential. The physical explanation of this laser behavior is given.