Ultrafast reflectivity and electron dynamic properties of Tb0.27Dy0.73Fe2 thin films

The ultrafast optical properties and electron dynamics of Tb0.27Dy0.73Fe2 thin film were studied using the femtosecond pump-probe technology. Experimental results revealed that the extremum of ΔR/R curves corresponding to the electron thermalization occurred around 100 fs, and with the decrease of thin film thickness, the average rate of reflectivity equilibration after extremum became faster. Amplitude of ΔR/R curves reach its maximum at 160 mW pump fluence and it turns zero at 0 mW. Echo waves were found in reflectivity waveform and the smaller the thickness of the thin film, the earlier the echo occurs. Time variation of the complex dielectric constant indicates that the absorption of thin films became greater with the increase of reflection at the surface after 0 ps delay time, but absorption of the thin film recovered to its initial state after 1 ps.