title: Bunching-induced optical nonlinearity and instability in cold atoms [Invited].
abstract: We report a new nonlinear optical process that occurs in a cloud of cold atoms at low-light-levels when the incident optical fields simultaneously polarize, cool, and spatially-organize the atoms. We observe an extremely large effective fifth-order nonlinear susceptibility of χ(⁵) = 7.6 × 10⁻¹⁵ (m/V)⁴, which results in efficient Bragg scattering via six-wave mixing, slow group velocities (∼ c/10⁵), and enhanced atomic coherence times (> 100 μs). In addition, this process is particularly sensitive to the atomic temperatures, and provides a new tool for in-situ monitoring of the atomic momentum distribution in an optical lattice. For sufficiently large light-matter couplings, we observe an optical instability for intensities as low as ∼ 1 mW/cm² in which new, intense beams of light are generated and result in the formation of controllable transverse optical patterns.
authors: Department of Physics and the Fitzpatrick Institute for Photonics, Duke University, Durham, NC 27708, USA. jag27@phy.duke.edu
authors: Joel A
authors: JA
authors: Greenberg
authors: Bonnie L
authors: BL
authors: Schmittberger
authors: Daniel J
authors: DJ
authors: Gauthier