Determination of the time dependence of n2 in air

Intense, directional UV emission from molecular nitrogen ions in an adaptively controlled femtosecond filament

“…The emitted signal is strongly modulated in time with the periodicities corresponding to the rotational revivals of both the ground and the excited ionic states, whereas its carrier frequency is modulated by the rotational revivals of neutral nitrogen molecules and is consistent with description given in Ref. [4]. Remarkably, all attempts to "seed" the "amplifier" at resonant UV transition frequencies invariably end up in optical losses because of resonant absorption.…”

“…The idea behind the use of such a pulse train is that relatively weak pre-pulses in the train produce alignment of nitrogen molecules at pulse separations corresponding to fractional revivals of the rotational wavepacket [4]. At the same time, a higher plasma concentration is expected when the intensity of the pulses in the train reaches the ionization threshold because the ionization probability for nitrogen molecules aligned along the laser polarization is about 4 times higher than for perpendicular orientation [5].…”

Four-Wave Optical Parametric Amplification in a Raman-Active Gas

“…When the signal pulse is delayed with respect to the pump pulse, no energy flow from the pump pulse into the signal pulse occurs. Only the frequency modulation of the signal pulse by the nuclear response is observable as in Figure 5, and as observed in the previous reports [13][14][15][16]18,19,24,25]. The Raman resonant FWM [30][31][32][33][34][35] may also be employed for the FWOPA.…”

Femtosecond Filamentation in Air

“…3) is split into an instantaneous component due to the electronic response in the polarization and a delayed component, of fraction α, due to stimulated molecular Raman scattering [69]. The function R(t) mimics the molecular response with a characteristic time τ dK and frequency Ω:…”