Study of Collapse Events in Ultraviolet Light Filaments Due to Transient Edge Effects

摘要

Intense, short light pulses can form filaments capable of propagating kilometers through the atmosphere. This is due to the nonlinear index of refraction of the atmosphere in response to the pulse's high intensity, which creates a self-focusing effect that further intensifies the pulse. This focusing is balanced by the formation of defocusing plasma by the pulse. A split-step propagation model was used to simulate the propagation of these pulses through the atmosphere and investigate the collapse of long ultraviolet pulses of 10-100 picoseconds in duration due to transient edge effects. The structures of individual collapse events in the pulse were characterized. The pulses collapsed linearly, yet independently of the initial pulse power. The number of collapses the pulse undergoes scaled with the initial power, and the plasma decay rate was found to dictate collapse event spacing. Additional collapses on the trailing edge of the pulse were also observed, and may have been created by the pulse field overflowing the grid used to model the propagation. Group velocity dispersion was included to add capabilities to model short pulses in the ultraviolet. Short pulses of 100 femtoseconds or less were observed to collapse in a manner similar to the longer pulses.