This is possible because the Kerr effect causes an index of refraction change in the medium, resulting in self-focusing of the beam.
[1] Filamentary damage tracks in glass caused by laser pulses were first observed by Michael Hercher in 1964.
[2] Filament propagation of laser pulses in the atmosphere was observed in 1994 by Gérard Mourou and his team at University of Michigan.
The balance between the self-focusing refraction and self-attenuating diffraction by ionization and rarefaction of a laser beam of terawatt intensities, created by chirped pulse amplification, in the atmosphere creates "filaments" which act as waveguides for the beam thus preventing divergence.
Competing theories, that the observed filament was actually an illusion created by an axiconic (bessel) or moving focus instead of a "waveguided" concentration of the optical energy, were put to rest by workers at Los Alamos National Laboratory in 1997.
Filament propagation in a semiconductor medium can also be observed in large aperture vertical cavity surface emitting lasers.
A nanosecond pulse is long enough to develop the air breakdown before the power reaches the GW order required for self-focusing.
Breakdown of gas produces plasma that has absorbing and reflecting effect so self-focusing is prohibited.
Such systems display a Kerr-like optical nonlinearity via photoreactive-based increases in the refractive index.
[10] The filaments form as a result of the self-trapping of individual beams, or modulation instability of a wide-area light profile.
[14][15] The locations of filament formation and propagation may be controlled by modulating the spatial profile of the input light field.
Such photo-reactive systems are able to produce filaments from spatially and temporally incoherent light, because the slow reaction responds to the time-average intensity of the optical field, whereby femto-second fluctuations wash out.
An interesting aspect of the filamentation induced plasma is the limited density of the electrons, a process which prevents the optical breakdown.
[17] This effect provides an excellent source for spectroscopy of high pressure with low level of continuum and also smaller line broadening.
[19] Flat panel dicing using short laser pulses is an important application due to the fact that as the glass substrates become thinner it becomes more difficult to improve the process yield using conventional diamond blade dicing techniques.
The substance in the filament is decomposed by the laser beam and can be discharged from the back surface, and a cavity is formed in the channel.
[citation needed] In July 2014, researchers at the University of Maryland reported using filamenting femtosecond laser pulses in a square arrangement to produce a density gradient in air which acted as an optical waveguide lasting on the order of several milliseconds.
[21] A field application was demonstrated in 2021, where kHz-repetition-rate 1030-nm terawatt Yb:YAG laser, installed in the vicinity of the 124-m-tall Säntis telecommunications tower was used to guide lightning strikes towards the tower's Franklin rod, opening up the possibility of future laser lightning rods.