One-spot and multispot processing for supermode stabilization

Abstract

Through employing an external mirror that is tilted by an angle beta = lambda/2d in the external cavity, whose round-trip cavity length is one-half a Talbot distance, a laser diode array (LDA) is made to oscillate with only an in-phase supermode. This makes the far-field distribution of the LDA have a central-single-lobe far-field pattern, and it also makes the output from the LDA be nearly diffraction limited. However, if the phase-locked output energy from the LDA is extremely high, then the thermal radiation from the output deforms the external mirror stochastically. This makes the tilt angle (beta) mismatched to the in-phase supermode, which results in undesirable supermode oscillations; so the far-field distribution of the LDA is no longer a central-single-lobe far-field pattern. Naturally, the intensity of the output from the LDA is attenuated, and the divergence loss is worsened. Therefore, suitable measures must be taken to guarantee the quality of the phase-locked output from the LDA. Accordingly, after analysis of the deformation of the external mirror, a novel one-spot and multispot processing (OMP) technology is developed. With special sensors, deformation of the external mirror is ascertained as a function of time. Then the deformation is compensated by appropriate equipment, which counteracts any bad influence on the angle beta. The experiment significantly demonstrates that only the in-phase supermode oscillated in an extremely high-energy LDA after the implementation of OMP, allowing such lasers to satisfy the requirements of high-quality laser applications. (C) 2010 Optical Society of America