Power-scalable system of phase-locked single-mode diode lasers

The direct use of diode lasers for high-power applications in material proc essing is limited to applications with relatively low beam quality and powe r density requirements. To achieve high beam quality one must use single-mo de diode lasers, however with the drawback of relatively low optical output powers from these components. To realize a high-power system while conserv ing the high beam quality of the individual emitters requires coherent coup ling of the emitters. Such a power-scalable system consisting of 19 slave l asers that are injection locked by one master laser has been built and inve stigated, with low-power diode lasers used for system demonstration. The op tical power of the 19 injection-locked lasers is coupled into polarization- maintaining single-mode fibers and geometrically superimposed by a lens arr ay and a focusing lens. The phase of each emitter is controlled by a simple electronic phase-control loop. The coherence of each slave laser is stabil ized by computer control of the laser current and guarantees a stable degre e of coherence of the whole system of 0.7. An enhancement factor of 13.2 in peak power density compared with that which was achievable with the incohe rent superposition of the diode lasers was observed. (C) 1999 Optical Socie ty of America OCIS codes: 140.3520, 140.2020.