Bright–Dark Light Bullets Under Third Harmonic Generation Conditions

Abstract

The possibility of forming a bright–dark light bullet during third harmonic generation has been studied, taking into account the mismatch between the phase and group velocities in a graded-index fiber with Kerr nonlinearity. The light bullet under consideration is a narrow two-color laser beam, along which a dark spot of intensity dip propagates with the group velocity at the third harmonic frequency. It has been shown that formation is possible with normal group velocity dispersion at the fundamental frequency. In this case, the refractive index of the fiber at the fundamental frequency must exceed the corresponding index at the third harmonic frequency, and the sign of the group velocity mismatch is of no fundamental importance. It has been established that the time duration of the dark spot exceeds a certain lower threshold, and the possible beam transverse radius range has lower and upper bounds. An increase in phase–group mismatch is accompanied by a decrease in the degree of transverse localization of the laser beam.