Direct observation of the generation of coherent optical phonons in thin antimony films by the femtosecond electron diffraction method

The generation of coherent optical phonons in an antimony film has been directly observed by the femtosecond electron diffraction method. The sample has been excited by a femtosecond laser pulse ($\lambda = 800$ nm) and probed with a pulsed photoelectron beam. Oscillations of the intensity corresponding to vibration frequencies of optical phonons excited by the laser have been observed in the obtained diffraction patterns: totally symmetric ($A_{1g}$) and twofold degenerate ($E_{1g}$) phonon modes of antimony and their combinations.