High Power, Low Loss, External Talbot Cavity

Abstract

An attractive technique for increasing the coherent output from semiconductor lasers is to coherently combine the output powers from individual high power single transverse mode lasers in an external Talbot cavity. In this presentation we report on the first demonstration of CW coherent high output power from a GaAlAs semiconductor laser array in a Talbot cavity. The cavity consists of an anti reflection coated 20 element laser diode array on 50 microns spacing, an imaging system and a 50% reflective flat output mirror. The chosen fill factor of the array optimizes mode discrimination and coupling between the lasers while minimizing the diffraction losses due to light diffracted out of the array. A half Talbot length cavity (round trip) is used such as to alleviate the need of a spatial filter in the cavity. Our experimental results show a CW diffraction limited far field of 250 mW and a differential efficiency of 29%. These power levels surpasses by far previous power levels obtained with semiconductor laser arrays in a Talbot cavity. Our results are found to be in good agreement with our theoretical model.