We demonstrate that bulk GaAs irradiated by heavyAu+ions shows efficient saturable absorption with subpicosecond recovery time and without any relaxation rate saturation up to excitation densities as high as1.6 mJ/cm2.A comparison with other types of ion irradiation shows that heavy-ion-irradiated GaAs is a very promising material for ultrafast optoelectronics and optical processing at high repetition rates. ©1998 American Institute of Physics.