Guiding of laser modes based on self-pumped four-wave mixing in a semiconductor amplifier.

We propose that self-pumped degenerate four-wave mixing may be used to produce novel diode laser systems where lasing is based on nonlinear guiding of the laser beams inside the active semiconductor. The fundamental process responsible for the interaction is spatial hole burning in semiconductor amplifiers. The gain and index gratings created by the modulation of the carrier density in the active gain medium lead to selective amplification of one spatial mode and suppression of all other modes. This mechanism allows the laser system to be operated far above its threshold with an almost diffraction limited output beam. The third order nonlinear susceptibility of the non-linear material, which determines the strength of the induced gratings, depends on the angle between the interacting beams in the four-wave mixing configuration. It is shown theoretically that a narrow range of angles exist where the induced gratings are strong and where mode suppression of higher order spatial modes are obtained simultaneously. Experimental evidence sustaining these findings is given.