Filament propagation
Encyclopedia
In nonlinear optics
, filament propagation is propagation of a beam of light
through a medium without diffraction
. This is possible because the Kerr effect
causes an index of refraction change in the medium, resulting in self-focusing of the beam.
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. If a light filament drops below the intensity needed for this dynamic balance, called modulation instability, it can merge with another filament and continue propagating without broadening as with all earlier means of sending light. The filaments, having made a plasma, turn the narrowband laser pulse into a broadband pulse having a wholly new set of applications.
Filament propagation in a semiconductor
medium can also be observed in large aperture vertical cavity surface emitting lasers.
Nonlinear optics
Nonlinear optics is the branch of optics that describes the behavior of light in nonlinear media, that is, media in which the dielectric polarization P responds nonlinearly to the electric field E of the light...
, filament propagation is propagation of a beam of light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
through a medium without diffraction
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
. This is possible because the Kerr effect
Kerr effect
The Kerr effect, also called the quadratic electro-optic effect , is a change in the refractive index of a material in response to an applied electric field. The Kerr effect is distinct from the Pockels effect in that the induced index change is directly proportional to the square of the electric...
causes an index of refraction change in the medium, resulting in self-focusing of the beam.
Filament propagation of laser pulses in the atmosphere was observed in 1994 by Gérard Mourou
Gérard Mourou
Gérard Mourou is a French pioneer in the field of electrical engineering and lasers. Along with Donna Strickland, he co-invented a technique called chirped pulse amplification, or CPA, which was later used to create ultrashort-pulse, very high-intensity laser pulses...
and his team at University of Michigan
University of Michigan
The University of Michigan is a public research university located in Ann Arbor, Michigan in the United States. It is the state's oldest university and the flagship campus of the University of Michigan...
. The balance between the self-focusing refraction and self-attenuating diffraction
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
by ionization
Ionization
Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...
and rarefaction
Rarefaction
Rarefaction is the reduction of a medium's density, or the opposite of compression.A natural example of this is as a phase in a sound wave or phonon. Half of a sound wave is made up of the compression of the medium, and the other half is the decompression or rarefaction of the medium.Another...
of a laser beam of terawatt intensities, created by chirped pulse amplification
Chirped pulse amplification
Chirped pulse amplification is a technique for amplifying an ultrashort laser pulse up to the petawatt level with the laser pulse being stretched out temporally and spectrally prior to amplification...
, in the atmosphere creates "filaments" which act as waveguides for the beam thus preventing divergence. If a light filament drops below the intensity needed for this dynamic balance, called modulation instability, it can merge with another filament and continue propagating without broadening as with all earlier means of sending light. The filaments, having made a plasma, turn the narrowband laser pulse into a broadband pulse having a wholly new set of applications.
Filament propagation in a semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
medium can also be observed in large aperture vertical cavity surface emitting lasers.