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

The authors demonstrate, using pump-probe experiments, that defects created by a 200MeV Au⁺ ion beam in bulk GaAs reduce the relaxation time of the saturable absorption of the material to as little as 200fs. The sample absorption is modulated over a spectral width of 50nm. 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.