Spectral shifts of the fundamental and third harmonic radiation in air induced by self-focused femtosecond laser pulses

The large spectral shifts of the fundamental and third harmonic waves (up to 20 nm and 50 nm, respectively) during femtosecond laser pulse filamentation in air have been demonstrated by using focusing lenses of long focal length. It was shown that in a wide range of laser intensities this process does not saturate and linearly depend on the pump pulse energy.