Filamentation in Atmospheric Air with Tunable 1100-2400 nm Near-Infrared Femtosecond Laser Source

Broadband conical third harmonic generation in femtosecond filament-modified fused silica

High repetition rate femtosecond filaments in transparent solids produce conical third harmonic generation due to filament-induced material reorganization in the form of periodic volume nanogratings. Here we report on conical third harmonic generation that accompanies supercontinuum generation in fused silica using broadly tunable femtosecond pulses. The measurement of third harmonic cone angles with driving wavelengths in the 1-3-μm range fully supports the noncollinear phase-matching scenario that involves a reciprocal lattice vector of the filament-inscribed nanograting. The nanograting provides an octave-spanning phase-matching bandwidth, as attested by the measurements of the angle-resolved spectra of broadband conical third harmonic emission.

Modification of Vibrational Parameters of a D∞h-Symmetric Triatomic Molecule in a Laser Plasma

We estimate theoretically the strong-field-modified vibrational parameters of three-atomic ABA molecules with D∞h symmetry in a laser-induced plasma. The linear CO2 and CS2 molecules in the X1Σg state are considered as examples. We show that double degeneracy of the Πu mode is removed due to reduction of the ABA molecule symmetry by the laser field. The linear form of ABA molecule is preserved, the bond length being elongated.

Characteristics of femtosecond laser-induced shockwaves in air

Dynamic characteristics of femtosecond laser-generated shockwaves are investigated in ambient air. The experiments are performed using a 360-fs pulsed laser at a wavelength of 1.03 µm, with laser intensities up to 5 × 10¹⁴ W/cm² (corresponding to about five times the air breakdown intensity threshold). Plasma and shockwave generation and propagation are visualized using a time-resolved transmission microscope. The maximum propagation velocity is in the order of Mach 30. By implementing a simple theoretical model, we find an initial pressure loading in the GPa range and shockwave pressure dropping down to MPa following propagation over few micrometers away from focus.