Filamentation of Mid-IR pulses in ambient air in the vicinity of molecular resonances

Abstract

Properties of filaments ignited by multi-millijoule, 90-fs mid-IR pulses centered at 3.9 μm are examined experimentally by monitoring plasma density and losses as well as spectral dynamics and beam profile evolution at different focusing strengths. By softening the focusing from strong (f=0.25 m) to loose (f=7 m) we observe a shift from plasma assisted filamentation to filaments with low plasma density. In the latter case, filamentation manifests itself by beam self-symmetrization and spatial self-channeling. Spectral dynamics in the case of loose focusing is dominated by the non-linear Raman frequency downshift, which leads to the overlap with the CO2 resonance in the vicinity of 4.2 μm. The dynamic CO2 absorption in the case of 3.9-μm filaments with their low plasma content is the main mechanism of energy losses and either alone or together with other nonlinear processes contributes to the arrest of intensity.

References in corpus (5)

• Higher-order Kerr terms allow ionization-free filamentation in gases
• Multiple filamentation induced by input-beam ellipticity
• Generation of long-lived underdense channels using femtosecond filamentation in air
• Energy deposition from focused terawatt laser pulses in air undergoing multifilamentation
• Sensitivity of propagation and energy deposition in femtosecond filamentation to the nonlinear refractive index

Cited by in corpus (4)

• Relativistic interaction of long-wavelength ultrashort laser pulses with nanowires
• Self-guiding of long-wave infrared laser pulses mediated by avalanche ionization
• Ionization rate and plasma dynamics at 3.9 micron femtosecond photoionization of air
• Physics and technology of Laser Lightning Control