Linewidth collapse in three-photon exciton-polariton spectra of CsI under pressure
Unusual phenomena occurring under hydrostatic compression in the near-band-edge structure of CsI crystals were examined using the nonlinear optical technique of three-photon excitation. The lowest one-photon allowed transition to the exciton-polariton A of gamma-4 symmetry redshifts, while the one-photon forbidden paraexciton C of gamma-5 symmetry blueshifts to a crossing of energies at 4.4 kbar. During this process, the A level exhibits strong spectral line narrowing by more than a factor of 10, while the C level intensity increases by about the same factor. We believe this is the first reported observation of pressure induced line narrowing of deep UV electronic states in solids.
Yoo
CH
Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA.
Lipp
MJ
Strachan
D
Daniels
WB