'Air Waveguides' Function Like Optical Fibers

A team from the University of Maryland has discovered how to make air behave like optical fiber, guiding light beams over short distances without losing power.

Using “air waveguides” the researchers have been able to enhance light signals. They said the signal was found to be 1.5 times stronger than a signal obtained without a waveguide.

The air waveguides were created over about 1 m using 10 Hz Ti:sapphire laser pulses at 800 nm, with pulse widths of 50 to 100 fs, and power up to 16 mJ. The pulses collapse into filaments because the laser light increases the refractive index of the air in the center of the laser beam, as if the pulse is carrying its own lens with it, the researchers said.

In the air waveguide, filaments leave holes in the air (red rods) that reflect light. Light (arrows) passing within these holes stays focused and intense. Courtesy of Howard Milchberg/University of Maryland.

In a previous study published in Physical Review X (doi: 10.1103/PhysRevX.4.011027), the researchers demonstrated that the filaments heat up the air as they pass through it, causing the air to expand and leave behind a hole of low density that has a lower refractive index than the air around it.

In this most recent study, the researchers used a laser to break down the air and create a spark. The air waveguide conducted light from that spark to a detector about a meter away. The researchers were able to generate a strong enough signal to analyze the chemical composition of the air that produced the spark.

Next, the researchers hope to show that the air waveguides can be used over longer distances (at least 50 m). If that works, they said, such waveguides could be used to conduct chemical analyses of the upper atmosphere or distant nuclear reactors.

Other potential applications include long-range communications, detecting atmospheric pollution, and development of high-resolution topographical maps and laser weapons.

The work was funded by the U.S. Air Force Office of Scientific Research, the Defense Threat Reduction Agency and the National Science Foundation. The research was published in Optica (doi: 10.1364/OPTICA.1.000005).

For more information, visit lasermatter.umd.edu.