filamentacji

Filamentation, or filamentacja in Polish, is a nonlinear optical propagation regime in which an ultrashort, high‑intensity laser pulse travels through a transparent medium as a narrow, self‑guided filament. The effect occurs when the pulse peak power exceeds the medium’s critical power for self‑focusing, causing the beam to contract due to the optical Kerr effect. In transparent media, the critical power is approximately P_cr ≈ 3.77 λ^2 /(8π n0 n2), where λ is the wavelength, n0 the linear refractive index, and n2 the nonlinear refractive index. As the intensity rises, ionization of the medium creates a plasma that defocuses the wave, balancing self‑focusing and producing a dynamic propagation channel.

A filament typically sustains over a considerable distance relative to the beam’s diffraction length, with core diameters from tens to several hundred micrometers and an ionized plasma channel that can extend for meters in air for femtosecond to picosecond pulses. The process also generates a broad spectral continuum (supercontinuum) and can emit terahertz radiation and acoustic shocks.

Filamentation is observed in various media, including air, liquids, and solids, and is exploited in applications such as remote sensing and LIDAR, spectroscopy, micromachining, and nonlinear optical studies. In fibers, high‑power pulses can produce multiple, intertwined filaments, a regime studied for high‑power supercontinuum generation and ultrafast pulse delivery. The phenomenon is a central topic in nonlinear optics, illustrating the balance between self‑focusing and plasma defocusing during propagation.