Regular "Breathing" of Single-Cycle Light Bullets in Mid-IR Filament

TL;DR

This study investigates the periodic intensity oscillations of mid-IR light bullets in LiF filaments, revealing a new understanding of their temporal evolution and the underlying physical mechanisms involved.

Contribution

It provides the first experimental observation of regular oscillations in light bullets in the mid-IR range and explains their origin related to wave packet velocity differences.

Findings

Periodic structure of color centers with 30 μm sections.

Oscillations increase as wavelength decreases.

Modulation caused by group and phase velocity differences.

Abstract

Experimental and numerical studies of a temporal evolution of a light bullet formed in isotropic LiF by Mid IR femtosecond pulse (2500 to 3250 nm) of power, slightly exceeding the critical power for self-focusing, are presented. For the first time regular oscillations of the light bullet intensity 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 a strictly periodic structure with a length of separate sections about 30 mcm, which increases with a laser pulse wavelength decreasing. It was shown that the origin of light bullet modulation is a periodical change of the light field amplitude of an extremely compressed single cycle wave packet in a filament, due to the difference of the wave packet group velocity and the carrier wave phase velocity.