The extreme nonlinear optics of gases and femtosecond optical filamentation

Abstract

Under certain conditions, powerful ultrashort laser pulses can form greatly extended, propagating filaments of concentrated high intensity in gases, leaving behind a very long trail of plasma. Such filaments can be much longer than the longitudinal scale over which a laser beam typically diverges by diffraction, with possible applications ranging from laser-guided electrical discharges to high power laser propagation in the atmosphere. Understanding in detail the microscopic processes leading to filamentation requires ultrafast measurements of the strong field nonlinear response of gas phase atoms and molecules, including absolute measurements of nonlinear laser-induced polarization and high field ionization. Such measurements enable the assessment of filamentation models and make possible the design of experiments pursuing applications. In this paper, we review filamentation in gases and some applications, and discuss results from diagnostics developed at Maryland for ultrafast measurements of laser-gas interactions. V C 2014 AIP Publishing LLC.

Beam deflection measurement of bound-electronic and rotational nonlinear refraction in molecular gases

“…It may be further improved upon to provide absolutely calibrated measurements by fully characterizing the beam interaction geometry, or by incorporating a gas jet within a vacuum chamber such that the induced deflection is uniform over a well-defined interaction length. The latter has been implemented by Wahlstrand et al in their single-shot spectral interferometry technique [39,48,54,55], where measurement of a thin (~2 mm) laminar gas flow within a chamber at low background pressure allows absolutely calibrated measurements. Experimental investigations of other gases may help validate and improve theoretical models of γ and the limitations of the Lorentz-Lorenz local field correction.…”

Study of filamentation with a high power high repetition rate ps laser at 103 µm

“…It is well known that at such high peak powers the pulse propagation is highly nonlinear. Pulses of femtosecond duration undergo filamentation, a process during which a dynamic competition between diffraction, self-focusing, plasma defocusing, and other nonlinear effects lead to the emergence of a beam with narrow diameter and high peak intensity (10 13-14 W/cm²) that is maintained over long distances [5][6][7][8][9].…”

Modeling of ultrafast laser pulse propagation

“…1 One of the recent trends concerns the push towards longer wavelengths. A lot of research over the last two decades in the nonlinear optics was made possible by the availability of high-power pulsed laser sources in the near infrared, this is the wavelength region where the efforts have been concentrated so far.…”