Extremely compressed wave packets in axicon-focused optical radiation

Using numerical modeling methods, we studied the peculiarities of light field dynamics during filamentation under the conditions of anomalous group velocity dispersion of mid-IR femtosecond pulses focused by axicon into lithium and calcium fluoride crystals. The appearance of specific points with the discontinuity of the wave front, which do not appear in the beam focused by a parabolic lens, was discovered. The wave front discontinuities were formed near the minima of the light field strength. A strictly periodic change in the spatial and energy parameters–the "breathing" of the light bullet formed in the axicon-focused beam as it propagated in the medium with material dispersion is demonstrated. The change in the oscillation period of the light bullet core with the change in the carrier wavelength does not depend on the radiation focusing method and coincides with the results of analytical estimates calculated for the Gaussian wave packet focused by the parabolic lens with the undistorted harmonic carrier.