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 c(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 ms). 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.