Optical parametric oscillation with distributed feedback in cold atoms

There is currently a strong interest in mirrorless lasing systems 1 , 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 lasers 2 and photonic crystal lasers 3 . The crossover regime between order and disorder, or correlated disorder, has also been investigated with some success 4 , 5 , 6 . Here, we report one-dimensional photonic-crystal lasing (that is, distributed feedback lasing 7 , 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. Researchers demonstrate one-dimensional photonic crystal lasing with the aid of a cold atom cloud that provides both gain and distributed feedback. Distributed feedback is due to the periodic distribution of the atoms trapped in a one-dimensional lattice enabling Bragg reflection, and parametric gain is provided by four-wave mixing.