Optical Filaments and Gas Dynamics in Air

Until now, the propagation dynamics of intense ultrashort laser pulses leading to optical filamentation in air has only been investigated in the frame of a dynamic balance between linear diffraction, Kerr self-focusing and plasma defocusing. This has led to the development of different theories surrounding the generation and persistence of optical filaments propagating over many Rayleigh lengths in air. These theories include wave-guiding model, moving focus model, dynamic spatial replenishment model and conical wave model. However, these models fail to capture the gas dynamics that arise from optical filaments interacting with air. In this work, we demonstrate that initial conditions are critical to the formation of optical filaments through the use of an aerodynamic window. Filament characteristics in air, such as spectral broadening, electrical conductivity and fluorescence, are measured and presented. Using these as diagnostic tools, we also show that the optical filamentation of ultrashort laser pulses can be enhanced at high repetition rates because of the thermal response of air, resulting from the interaction of each laser pulse with the modified atmospheric density distribution left behind by the preceding pulse. This is explained by the sudden deposition of energy by a filament in the air which generates a cylindrical shock wave, leaving behind a column of rarefied air. This low-density region persists for an extended period and can materially affect the propagation dynamics of an ensuing pulse that follows before the low-density region has relaxed sufficiently to ambient conditions. By further increasing the repetition rate, the onset of ionization is shifted downstream and the spectral continuum displays a stronger broadening on both sides of the original pulse spectrum. This gas dynamic interaction regime of filamentation can be utilized to enhance the length and spectral width of filaments for remote sensing and long range laser-induced high voltage discharges.

Name thesis:degree_name

Optical Science and Engineering

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Optical Science and Engineering

Year

2014

Author dc:creator

• Yeak, Jeremy

Contributors dc:contributor

• Schamiloglu, Edl
• Gilmore, Mark
• Walters, Edward
• Roderick, Norman
• Sheik-Bahae, Mansoor

Language dc:language

English

Identifier

https://digitalrepository.unm.edu/ose_etds/48

OAI identifier oai:identifier

oai:digitalrepository.unm.edu:ose_etds-1047