In this work we present experiments by focusing 42 femtosecond laser pulses in air using three different focal length lenses: f=100, 30 and 5 cm. For the longest focal length, only the filament, which is a weak plasma column, is observed. When the shorter focal length lens is used, a high density plasma is generated near the geometrical focus and coexists with a weak plasma channel of the filament. Under the tightest focusing condition, filamentation is prevented and only a strong plasma volume appears at the geometrical focus.
© 2005 Chinese Optics Letters
(020.4180) Atomic and molecular physics : Multiphoton processes
(300.2530) Spectroscopy : Fluorescence, laser-induced
(320.7120) Ultrafast optics : Ultrafast phenomena
(320.7150) Ultrafast optics : Ultrafast spectroscopy
W. Liu, Q. Luo, and S. L. Chin, "Competition between multiphoton/tunnel ionization and filamentation induced by powerful femtosecond laser pulses in air," Chin. Opt. Lett. 1, 56-59 (2003)