Optical parametric oscillation with distributed feedback in cold atoms

Abstract

There is currently a strong interest in mirrorless lasing systems1, in which the electromagnetic feedback is provided either by disorder (multiple scattering in the gain medium) or by order (multiple Bragg reflection). These mechanisms correspond, respectively, to random lasers2 and photonic crystal lasers3. The crossover regime between order and disorder, or correlated disorder, has also been investigated with some success4,5,6. Here, we report one-dimensional photonic-crystal lasing (that is, distributed feedback lasing7,8) with a cold atom cloud that simultaneously provides both gain and feedback. The atoms are trapped in a one-dimensional lattice, producing a density modulation that creates a strong Bragg reflection with a small angle of incidence. Pumping the atoms with auxiliary beams induces four-wave mixing, which provides parametric gain. The combination of both ingredients generates a mirrorless parametric oscillation with a conical output emission, the apex angle of which is tunable with the lattice periodicity.