PICOSECOND NONLINEAR SPECTROSCOPY OF QUANTUM-SIZE PBTE FILMS

We propose a new and promising technique to study quantum-size structu res. In ultrathin monocrystalline PbTe films with thicknesses L = 6, 1 8, and 30 nm, we have examined this technique, based on two-photon opt ical excitation of the renormalized electronic structure and revealed a sharp dependence of frequencies of two-photon resonant transitions o n L. We explained this result within the framework of a model taking i nto account the real PbTe band structure, electron-electron and electr on-phonon interactions, and interband and intraband redistribution of free carriers. We have estimated the characteristic time of interband polarization decay at T-2 greater than or equal to 300 fs and haved an alyzed the transformation of the nonlinear response for the case L-->i nfinity. (C) 1996 American Institute of Physics.