Phase-locked array of 25 broad-area lasers

摘要

In the case of single broad area diode lasers it was shown that the 20 stripes of the active zone can be coherently coupled to achieve almost diffraction limited light of more than 400 mW with beam propagation factors of M~2=1.2. This corresponds to a twelve-fold overall improvement in brightness. The basic idea is to operate the laser under an angle with respect to its optical axis in a stable resonator mode along its slow axis. The resonator is simple, does not possess complicated or expensive elements and can be arranged in a compact and robust way. For bars of 25 broad area lasers a coherent operation could be demonstrated. Coupling was achieved by use of a diffractive optical element which operated as a 1:25 spatial multiplexer. Coherent operation existed for external seeding, for a regenerative amplifier, and for a laser oscillator. It could be shown that the phases lock but some temporally stable mutual phase differences still exist. The arrangement operates without active phase control and even without separate alignment of the single emitters. In the case of seeding the extracted coherent light possesed a beam propagation factor of M~2<2 which is an improvement of more than three orders of magnitude as compared with the freely running case.