Understanding the nonlinear phase and frequency shift of an ultrashort light pulse induced by an inertial third-order optical nonlinearity

Abstract

Inertia of optical nonlinearity is shown to distort the temporal profile of the intensity-dependent phase shift of an ultrashort laser pulse relative to the phase induced by the instantaneous optical nonlinearity. We demonstrate that a weakly inertial optical nonlinearity, whose response time is smaller than the pulse width, tends to redshift the light field and generates a cubic-phase correction to the quadratic phase, thus complicating the chirp of the spectrally broadened field. For very short light pulses with pulse widths shorter than the response times of optical nonlinearity, the redshift and cubic-phase terms often dominate the nonlinear phase shift, giving rise to phase profiles significantly different from those induced by instantaneous optical nonlinearity.