Morphology of femtosecond laser-induced structural changes in MgAl2O4 crystal

The morphology of structural changes in MgAl2O4 transparent ceramic (MATC) crystal ablated by femtosecond laser pulse has been investigated. Experiments were performed using a commercial Ti:sapphire laser system with 800 nm/50 fs and the repetition ratio of 1 kHz. The damage threshold and ablation area for MgAl2O4 transparent ceramic are investigated. The result shows that the darkening threshold and the damage threshold of MATC are measured to be 6.0 x 10(12) W/cm(2) and 2.4 x 10(13) W/cm(2), respectively. The ablated spots are examined by means of a charge coupled device (CCD) camera, scanning electron microscopy (SEM) and atom force microscopy (AFM). The infrared transmission ratio (IR transmission ratio) properties of MATC crystal ablated by femtosecond laser pulse are measured by micro-IR spectra. The result shows that the damaged area will increase linearly with the increasing energy of single pulse while will be approximate satisfied with Boltzmann distribution with the increasing number of multiple pulses. The spot ablated at optimized energy pulses (near the damage threshold energy) can improve the IR transmission ratio of MATC crystal from 82% to 86%. Furthermore, the periodic ripples about 100 nm in width and 200 nm in neighbouring ripples distance are formed on the bottom surfaces of ablation holes.