Coherence and beam shaping in Quantum Cascade Lasers

摘要

Mid-infrared beam shaping concepts are presented, which rely on coherent emission from QCLs. Grating coupled surface emitting quantum cascade ring lasers allow for far-field tuning, ranging from highly symmetric spot- to ring-shaped beam patterns, depending on the grating period. In single-mode operation, the devices exhibit low beam divergence, represented by a full width at half maximum of ～3°. Moreover, a tree shaped resonator is investigated, which enables coherent parallel coupling of six laser elements into a single waveguide by means of several Y-junctions. The lasers were investigated in terms of optical power, near and far field characterization. Phase-locking was observed and leads to in-phase emission on both sides of the devices. Both concepts demonstrate the feasibility of high-brightness mid-infrared quantum cascade lasers with prospective applications in spectroscopy and high power laser arrays.