THEORY OF OPTICAL-PROPERTIES IN NONSTATIONARY MEDIA CREATED BY FEMTOSECOND PULSES - LINEAR CASE

In ultrashort (femtosecond) pump-probe spectroscopy, the pump pulse creates a nonstationary medium, while the probe pulse propagates in such a medium. The constitutive equations of the nonstationary media are different from those of the stationary media. Both constitutive equations and electrodynamic properties of the nonstationary media are analyzed. The conjecture that by dispersing the probe pulse, having a broad spectrum, in a spectrograph after it passed through the sample one can achieve simultaneously high resolution both in time and frequency, is examined. Such a conjecture is based on the use of the stationary electrodynamics formula for the probe pulse absorption. Using the nonstationary electrodynamic relations, derived in the paper, it is shown that probe pulses yield time-resolved spectra subjected to usual time-frequency limitations.