Filamentation induced by collinear femtosecond double pulses with different wavelengths in air

Filamentation induced by collinear femtosecond double pulses with different wavelengths (400 nm + 800 nm) in air is investigated by measuring the filament spectra along the propagation axis. By changing their energies and the time delay between them, the role of each pulse in the filamentation is investigated. Though the two pulses do not overlap in time, the filament generated by the previous pulse will interact with the latter one, thus affecting the filamentation process. Each pulse plays a different role when the time delay and input energy are different: As the energy of the 800 nm pulse is relative high (similar to 600 mu J), the 400 nm pulse has inhibitory and supplementary effects on the filament generated by the 800 nm one as it is prior to and behind the 800 nm one, respectively, which ultimately influences the filament length and strength; however, as energy of the 800 nm pulse decreases to 340 mu J, the filament mainly results from the 400 nm pulse and the 800 nm one just plays an auxiliary role. This study provides an effective way to control filamentation. (C) 2015 AIP Publishing LLC.