Modal Behavior, Spatial Coherence, and Beam Quality of a High-Power Gain-Guided Laser Array

In this paper, we investigate the modal behavior and the spatial coherence properties of a gain-guided laser array emitting an optical output power of more than 50 W in quasi-continuous-wave operation at a wavelength of 1070 nm and above. The lateral near- and far-field intensity profiles and the Wigner distribution function were measured from low to high output power. The array modes were calculated by solving the waveguide equation taking into account the power-dependent temperature distribution and were also experimentally determined by a modal decomposition of the cross spectral density. The analysis revealed that, at a low power, a single array mode lases, whereas at high power, multiple single stripe modes dominate the lasing due to the thermally induced index rise under the stripes.