Propagation of self-focusing laser pulses in atmosphere: experiment versus numerical simulation

Femtosecond filamentation in transparent media

“…This value of is in good agreement with measurements by Ripoche et al (1997). In the same paper (Pitts et al, 2004), simulation results obtained by using the nonlinear index for fused silica n 2 = 2.5 × 10 −16 cm 2 /W and R = 84 × 10 12 rad/s, = 20 × 10 12 rad/s, = 0.15 were compared favorably with single-shot spectral experimental data. Couairon et al (2005b) inferred a slightly larger value for the nonlinear index of fused silica (n 2 =3.5×10 −16 cm 2 /W at 800 nm) by comparison of measured and numerically obtained positions for the nonlinear focus were filamentation starts.…”

“…On the basis of systematic confrontation of numerical with real experiments, several works were performed with the specific goal of determining the values of specific physical parameters, in the filamentation regime, to be introduced in the models. Among these works, Pitts et al (2004) favorably compared theoretical predictions of spectral, temporal, and transverse spatial widths, obtained by model (47)-(51) of Section 2.2.5 with dispersion limited to third order, with measurements in air for several propagation distances over a range of energies up to 2 mJ for pulse duration of 200 fs. By use of these data, a simple fit of the nonlinear refractive index and delayed Raman contribution fraction yielded values of n 2 = 2.8 × 10 −19 cm 2 /W and = 0.58, respectively.…”

Linear and Nonlinear Femtosecond Optics in Isotropic Media - Ionization-Free Filamentation

“…The TH or THz term (the second nonlinear term in the brackets) practically does not influence the intensity picture during propagation. In conclusion of this paragraph, we should point out that our non-paraxial ionization-free model (20) and (21) is in good agreement with the experiments on spatial and spectral transformations of a fs pulse in a regime near the critical P ≥ P cr . Such transformation of the shape and spectrum of the fs pulse is typical in the near zone, up to several diffraction lengths, where the conditions for narrow-band pulse are satisfied △k z << k 0 .…”

“…We use AE equations (20) and (21) to simulate the propagation of a fs pulse, typical for laboratory-scale experiments: initial power P = 2P kr , center wavelength λ = 800 nm, initial time duration t 0 = 400 fs, corresponding to spatial pulse duration z 0 = v gr t 0 ∼ = 120 µm,andwaistr 0 = 120 µm. Fig.4 presents the evolution of the spot |A(x, y| 2 of the initial Gaussian laser pulse at distances…”

“…The plasma and higher-order Kerr terms are too small to prevent self-focussing. The observation of long-range self-channeling (18)(19)(20) without ionization also leads to change the role of plasma in the laser filamentation. In addition, there are difficulties with the physical interpretation of the THz radiation as a result of plasma generation.…”