Mode control in broad-area diode lasers by thermally induced lateral index tailoring

Broad-area diode lasers that emit in the fundamental mode under short-pulse excitation are observed to evolve into higher order lateral modes with increasing pulse width. Our data provide convincing evidence that the lateral refractive index profile arising from junction heating plays a dominant role in determining the lateral emission modes in these devices for long-pulse and cw operation. Furthermore, we show that an external focused laser heat source can be used to modify the lateral index profile in a broad-area laser and thus control the lasing mode. In particular, we demonstrate that ≲50 mW of absorbed heating power is sufficient to counteract the effects of internal junction heating and restore fundamental mode operation at cw injection currents as high as 1.5 Ithreshold. Our results suggest that fundamental mode operation of broad-area devices at high-power levels might be realized by incorporating a tailored lateral index profile to compensate for internal junction heating.