Abstract

The Kramers-Kronig (K-K) relations¹ connect the real and imaginary parts of the linear susceptibility χ(ω). It was also proved that the K-K relations can be extended to nonlinear optics as far as the causality condition is satisfied.² In particular in steady-state pump-probe spectroscopy, the usual K-K relations hold to all orders in the pump field if the pump frequency is fixed. On the other hand, the applicability of the K-K relations in time-resolved spectroscopy is not obvious. It has been difficult so far to study the time-resolved dispersion relations because of the experimental difficulties in measuring time-resolved difference phase spectra (DPS).

© 1992 Optical Society of America