- We have investigated the effects of gamma-ray irradiation on the optical properties of visible strained multi-quantum-well lasers. It was observed that the power emission from the laser fell progressively and the wavelength linewidth increased with increase of irradiation. The laser emission properties recovered as the duration of the subsequent dc current increased. The far-field beam emission divergence was reduced after irradiation. We propose that these irradiation effects may be caused by structural changes in the strained thin layers, due to an atomic displacement and migration between layers and due to changes in the degree of strain. This affects the layer’s atomic composition, which changes the band-gaps’ energy levels and the indexes of refraction, and as a result, the carrier and optical confinements, respectively. © 2002 American Institute of Physics.