Author Topic: Air waveguide improvement for lasers going through atmosphere  (Read 1099 times)

Offline Asteroza

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New technique for improving laser transmission in air, by jacketing a laser beam with a concentric ring femtosecond pulse laser beam. Pulse laser causes outward and inward heat expansion shocks, the inward of which creates a low density and high density zone (I assume the center is high density here?). That low density zone effectively creates a waveguide of sorts, lasting around 100ms. Demo seems to use discrete jacketing beams rather than a continuous jacketing ring beam though.

Probably applicable to high power lasers through atmosphere (SPS power downlinks, externally beamed power SSTO's). A different take from previous path clearing methods, where a pulse laser was being used to "explode" the whole laser path from beam core/center outwards.

Pulse laser, so what exactly would be needed to make the air waveguide a usable steady state phenomenon?

Offline Burninate

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Crazy.  Lasers which substantially influence the air they pass through are nearly technology indistinguishable from magic to me.  I can't even imagine most of the applications.

Offline JeanPierre_LeRouzic

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From the article:"Among the most popular schemes are light detection and ranging (LIDAR) and laser-induced breakdown spectroscopy (LIBS). In LIDAR, the signal is induced by a laser pulse, either by reflection or backscattering from distant surfaces or atmospheric constituents.
Some recent schemes for optical stand-off detection use femtosecond filamentation, which occurs when an ultrashort pulse, propagating through a transparent medium such as the atmosphere, experiences focusing from its self-induced Kerr lens. When self-focusing is stronger than diffraction, the beam mode collapses into a tight core or filament
The beam collapse is then arrested by plasma defocusing
In this paper we show that femtosecond filament air waveguides can collect and transport remotely-generated optical signals while preserving the source spectral shape

My understanding is that it is a two steps process, first a laser generates optical signals on the target (including through ionic effects) then the "pseudo optical fiber" which is the subject of this article, helps to convey back the signal with little noise/attenuation to the source. This "pseudo optical fiber" is generated by the ionization on the point of impact of the laser. The ionization generates filaments that build the "pseudo optical fiber". Even if each filament is one meter long, they can react over each other and create some lens effect.

Obviously it can't be used *in* space but it could be used from LEO to collect information about the Earth surface.

Offline cordwainer

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I imagine that when they say "out of thin air" they actually mean "thin air". Seems like this technique would be hampered by weather, pollution and water molecules. Still this might allow faster switch times within FOT's and allow you to make a "digital" waveguides that could replace fiber-optic cables for really large transfers of data. Most laser or radio waveguides rely on transferring analog waveforms to digital pulses, this could allow high throughput of digital pulses with fewer transmission losses.

Online Stormbringer

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Yeah, it might not apply to bad lasing conditions like rain and so forth but what if the "jacketing" laser pulses are extremely powerful?
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