Abstract

Unstable-resonator diode lasers¹ and semiconductor amplifiers² can produce diffraction-limited high-power output. It is known that filamentation and thermal lensing (caused by a lateral temperature variation) inside the laser cavity are common reasons for the collapse of spatial coherence at high drive current. While theoretical models³ have been developed to describe these limitations of diffraction limited power, to the best of our knowledge, these effects have to date been observed only in the near-field outputs of semiconductor lasers. Using an indium titanium oxide (ITO) ohmic contact, which is transparent and conductive, on the GaAs substrate side of our unstable-resonator semiconductor lasers,¹ we have been able to monitor the whole laser cavity beneath the stripe and have observed the detailed 2D behavior of filaments in these lasers. This technique should be generally applicable to other lasers and power-amplifier structures.

© 1995 Optical Society of America