Bad Phonon Good Phonon

Dr. David Hurley
Science and Technologyt
Idaho National Laboratory

By simply shining a pulsed laser beam on a material, much can be learned about the fundamental nature of matter.  For the case of laser irradiation of semiconductors, in the first few femtoseconds (10-15s), the photons that compose the laser beam interact with the valence electrons.  After a few picoseconds (10-12s) the kinetic energy of the valence electrons is converted into kinetic energy of the nuclei (phonons).  Low frequency phonons are identified with acoustic waves while high frequency phonons are identified with heat pulses. In this context heat and sound are governed by the same physical process.  This presentation will examine at an undergraduate physics level, how we use both high frequency and low frequency phonons to gain fundamental information about the evolution of thermal and mechanical properties of nuclear materials.