Regular ‘breathing’ of a near-single-cycle light bullet in mid-IR filament

Abstract

Experimental and numerical studies of a temporal evolution of a light bullet formed in isotropic LiF by mid-IR femtosecond pulse (2600–3350 nm) of power, slightly exceeding the critical power for self-focusing, are presented. For the first time regular oscillations of the light bullet field peak amplitude during its propagation in a filament were registered by investigation of induced color centers in LiF. It was revealed that color centers in a single laser pulse filament have the strictly periodic structure with a length of separate sections about 30 μm, which increases with a laser pulse wavelength decreasing. It was shown that the origin of a light bullet modulation is a periodical change of the light field amplitude of a near single-cycle wave packet in a filament, due to a difference of the wave packet group velocity and the carrier wave phase velocity.