Sub-picosecond wideband efficient saturable absorber created by high energy (200 MeV) irradiation of Au+ ions into bulk GaAs

The authors demonstrate, using pump-probe experiments, that defects created by a 200 MeV Au⁺ ion beam in bulk GaAs reduce the relaxation time of the saturable absorption of the material to as little as 200 fs. The sample absorption is modulated over a spectral width of 50 nm. The integrated value of the absorption modulation thus shows the high absorption efficiency of the irradiated material. A very small variation in relaxation time is found when the density of photocreated carriers is increased to ~5×10¹⁸cm^-3 . This material appears to be very promising for applications in optical processing and ultrafast measurement at high pulse repetition rates