Digital Reconstruction at Femtosecond Laser-Induced Dynamic Surface Changes

Abstract

We present the pump-probe technique and the off-axis digital holography to monitor light-induced dynamic changes in the Cr film on the glass. Femtosecond pulses from a Ti:sapphire laser oscillator were split into pump pulses and probe pulses. The pump pulses were used for inducing the phase change of the Cr film and the probe pulses were used for probing it in a Mach-Zehnder interferometer. The sample was placing in one arm of the interferometer. A delay line was used for changing the probe pulses. By changing the delay line of the probe pulses, the probe pulses were measured at different time delays between the pump and the probe pulses. A dynamic interference holography produced by the probe beam passing through the sample is then captured by a CCD camera. A reconstruction algorithm was used to obtain the sample time evolution of both amplitude and phase-contrast images. Using this setup, we study the dynamic surface deformation in a thin Cr film. Experimental results are given to show that the amplitude and phase-contrast images are well reconstructed. This technique can be used as a characterization tool to precisely monitor dynamic changes induced by femtosecond laser pulses.