Through Thick and Thin

Making Optical Waveguides Out of Thin Air

The filaments are created when pulses from a 10 Hz Ti:sapphire laser collapse the air into a narrow filament, increasing the refractive index of air in the center of the beam. The filaments heat the air as they travel, causing it to expand, and leave behind an air density depression (or hole) with a lower refractive index than the surrounding air.