Speaker
Description
Silicon has three optical phonons, which remain inaccessible with linear
optical techniques. Here we demonstrate that time-resolved pump-probe spectroscopic ellipsometry enables the detection of optical phonon responses at both the Brillouin zone center and -edge. Using pump pulses with photon energies below the indirect bandgap of silicon, we leverage two-photon absorption to induce sub-bandgap excitation. Transient optical effects have been probed in the 1.9-3.6 eV spectral range with pump-probe time delays from 50 fs to 4.5 ns. We observed distinct features indicating optical transitions involving entangled (coherent) electron phonon states:
1) a structure at the E1 critical point persisting for 4.5 ns;
2) longitudinal optical phonons with an energy spacing of 57±9 meV, lasting approximately 300 fs
and
3) two-phonon replicas, exhibiting a spacing of 81±7 meV.
Details of the presentation can be found in the main text and in the supplementary material of https://doi.org/10.1063/5.0288893.