This thesis presents a systematic study on the characterising ultrafast dynamics of photo excited carriers in hydrogenated nano crystalline silicon (nc-Si:H) and porous silicon (PS) materials using the ultrafast optical pump probe spectroscopy approaches. The work involves the ground state optical property detection and optical model simulation, ultrafast time resolved pump probe measurements and pump probe data analysis processes. Applying the novel pump probe detection methods, the study explores the carriers concentration, carriers recombination property, scattering rate and conductivity of photo excited semiconducting nano materials.