Self-seeded lasing in ionized air pumped by 800 nm femtosecond laser pulses

Abstract

We report on the lasing in air and pure nitrogen gas pumped by a single 800 nm femtosecond laser pulse. Depending on gas pressure, incident laser power and beam convergence, different lasing lines are observed in the forward direction with rapid change of their relative intensities. The lines are attributed to transitions between vibrational and rotational levels of the first negative band of the singly charged nitrogen molecule-ion. We show that self-seeding plays an important role in the observed intensity changes.

Study of the population inversion mechanisms and superradiance on ion transitions of molecular nitrogen in the filament

“…As for its photon the energy is 1.3 eV, then for multiphoton ionization of molecular nitrogen in the upper laser level (18.7 eV) requires the 15 photons (Figure 6). Thus the excess energy above B 2 Σ u + (v=0) state is 0.88 eV, while in the work with λ = 800 nm [11,12,[15][16][17] 13 photons requires, which gives a total energy of 20.15 eV and exceeding of the upper laser level at 1.45 eV. I.e.…”

“…From the uncertainty relation for Gaussian beam (∆ω × ∆t ≥ 0.441) the pulse duration this radiation should be no less 250 -350 fs. Note that in [15] this duration was 900 fs. Thus the implementation in our conditions the superradiance lines of 427.8 and 391.4 nm pumped by the fundamental harmonic is due, in our opinion, a number of favorable factors.…”

“…A little later in the same year the super-radiance at this wavelength was obtained by irradiation of pure nitrogen in the cell [14] and the air [16,17] by radiation of femtosecond laser at λ = 800 nm. Thus in [11,12,[15][16][17] it has been shown that as the initiation of radiation, resulting in an exponential increase of photon on laser transitions of the molecular nitrogen ions the photons of supercontinuum (laser white light) are. Despite the fact that at present the number of experimental studies in this field is growing but the mechanisms creating an inversion population and generating in plasma of filament at the above transitions in the molecular ion of nitrogen is not completely clear.…”

Coupling ofN2+rotational states in an air laser from tunnel-ionized nitrogen molecules

“…Recently, free-space lasers generated during femtosecond laser filamentation in nitrogen gas have attracted considerable attention [1][2][3][4][5]. The nitrogen lasers not only provide new opportunities for remote sensing in ambient air, but also extend the territory of strong field molecular physics [6][7][8].…”

Measurement of the Nonlinear Refractive Index of Air Constituents at Mid-Infrared Wavelengths

“…Good agreement is found with theoretical models of  (3) . Our results are essential for accurately simulating the propagation of ultrashort mid-IR pulses in the atmosphere.Filamentary propagation of intense ultrashort laser pulses in atmosphere for < ~1 m has been a subject of extensive study [1,2], finding applications in the generation of terahertz radiation [3], high harmonic generation [4], air lasing [5][6][7], and remote inscription of optical waveguides into air [813]. It has been anticipated that new regimes of laser filamentation are possible at longer wavelengths, such as in the midinfrared (mid-IR,  ~ 1.5-10 m), where beam collapse arrest may occur through harmonic walk-off rather than plasma-induced refraction [14].…”