Controlling phase change through ultrafast excitation of coherent phonons.

For semimetals such as bismuth, ultrafast femtosecond laser-excited coherent phonons at laser fluences below the damage threshold have been studied extensively. In this work, we investigate whether or not coherent phonon oscillations contribute to material's permanent damage, or can enhance or suppress such damage. We employed temporally-shaped femtosecond pulses to either enhance or cancel coherent phonon oscillations. Our results showed a clear difference in material's damages caused by femtosecond pulses that enhance and cancel phonon oscillations, demonstrating the possibility of controlling phase changes by coherent control of phonon oscillations.