Air waves could behave as optical cables

Imagine instantaneously running an optical cable or fibre to any point on Earth, or even into space. A US scientist wants to do exactly that!
Howard Milchberg, professor of physics and electrical and computer engineering at the University of Maryland and his lab have used an "air waveguide" to enhance light signals collected from distant sources.
These air waveguides could have many applications, including long-range laser communications, detecting pollution in the atmosphere, making high-resolution topographic maps and laser weapons.
Because light loses intensity with distance, the range over which such tasks can be done is limited. Even lasers, which produce highly directed beams, lose focus due to their natural spreading, or worse, due to interactions with gases in the air.

Fibre-optic cables can trap light beams and guide them like a pipe, preventing loss of intensity or focus.
But solid optical fibres can only handle so much power, and they need physical support that may not be available where the cables need to go, such as the upper atmosphere.

Now, Milchberg's team has found a way to make air behave like an optical fibre, guiding light beams over long distances without loss of power.
Milchberg's air waveguides consist of a "wall" of low-density air surrounding a core of higher density air. The wall has a lower refractive index than the core - just like an optical fibre.

Milchberg, physics graduate students Eric Rosenthal and Nihal Jhajj, and associate research scientist Jared Wahlstrand, broke down the air with a laser to create a spark.
An air waveguide conducted light from the spark to a detector about a metre away. The researchers collected a strong enough signal to analyse the chemical composition of the air that produced the spark.
The signal was 1.5 times stronger than a signal obtained without the waveguide. That may not seem like much, but over distances that are 100 times longer, where an unguided signal would be severely weakened, the signal enhancement could be much greater.

Milchberg creates his air waveguides using very short, very powerful laser pulses. A sufficiently powerful laser pulse in the air collapses into a narrow beam, called a filament.
This happens because the laser light increases the refractive index of the air in the centre of the beam, as if the pulse is carrying its own lens with it.
Milchberg showed previously that these filaments heat up the air as they pass through, causing the air to expand and leaving behind a "hole" of low-density air in their wake.
The research was published in the journal Optica.