Abstract

In conventional lasers stimulated emission is spatially coherent and the frequencies of operation (commonly called longitudinal modes) are determined by the resonator’s eigenmodes. In 1966, Ambartsumyan et al. proposed a new type of laser [1] (now known as a kind of random lasers [2]) where a nonresonant feedback occurs via reflection off a phase scrambling medium instead of a rear laser mirror. In such a laser the amplified photons scatter multiple times and do not return to their initial location periodically, so it is impossible to form a spatial resonance. This means that the feedback in the laser is used only to return part of energy back to the active laser medium without any selection of the resonant waves (modes). The absence of the resonant feedback means that the spectrum of the generated laser emission should be continuous, without discrete modes at certain resonant frequencies [3]. In practice, however, such random lasers commonly generate narrow stochastic spikes on the top of the laser emission spectrum. Similar regimes have been achieved in all-fiber laser configurations [3, 4].

© 2011 Optical Society of America