Efficient Photorefractive Beam Combining with High-Power Injection-Locked Semiconductor Laser Arrays

Abstract

Much research effort is currently devoted to the improvement of the output power and beam quality of semiconductor diode lasers. One of the most successfull approach is the concept of phase-locked laser arrays [1]. When the individual emitters of such arrays are separated by a distance of the order of a few wavelengths, phase locking between them occurs and coherent, diffraction-limited operation of the array can in principle be achieved [2]. However, when very high power operation is needed, thermal considerations imposes a large separation between the individual emitters or a division of the total array into several uncoupled sub-arrays. This is in particular the case of laser bars [3] and of many two-dimensional arrays [4]. To achieve coherent and diffraction-limited operation in one single emission lobe from such devices, an external control of the phase of otherwise independent elements and a beam combining technique are needed. Injection locking and wave mixing in photorefractive BaTiO3 are good candidates for such functions [5-7]. Energy transfer from an injection-locked array by two-wave mixing in BaTiO3 has been reported in Ref. [8], with a maximum of 1% efficiency. The purpose of this paper is to describe and demonstrate highly efficient energy transfer with an injection-locked array using two-wave mixing in BaTiO3.