Electronic structure measurements in KI at high pressure using three-photon spectroscopy

This work is the first report of the use of nonlinear optics techniques to probe the pressure dependence of electronic energy levels in a solid. An advantage which may be significant is that for the multiphoton processes involved, relatively low-energy photons that are not absorbed by the cell windows can probe states having energies which would be strongly absorbed by the windows in a one-photon excitation. The measurements follow the pressure dependence of the energetically lowest polariton in KI using the three-photon-spectroscopy method.