Five-wave mixing investigation of electron dynamics at silicon surfaces

A surface-sensitive purely optical technique is demonstrated for the investigation of ultrafast relaxation processes of excited electronic surface states. We employed a synthesis of degenerate four-wave mixing (DFWM) and optical second-harmonic generation (SHG) to study the coherent and incoherent dynamics of dangling-bond states at silicon surfaces with femtosecond time-resolution. The resulting five-wave mixing process is characterized by a #chi#"("4")-tensor; like the #chi#"("2")-processes SHG or SFG it is dipole-forbidden in the bulk of centrosymmetric materials, like crystalline silicon. The surface-sensitive probe can be described by diffraction of photons at a transient population grating with their upconversion to the second harmonic. (orig.)Available from TIB Hannover: RN 5339(267) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman