Femtosecond laser pulses can move a microscopic bubble inside solids, report scientists from Osaka University in Japan in the July 15 issue of Optics Express.

They focused a Ti:sapphire laser producing 130-fs, 800-nm pulses at a depth of 200 µm inside a 3-mm-thick plate of calcium fluoride, creating a void. Subsequent pulses moved the bubble as much as 2 µm opposite the direction of laser propagation. By shifting the focus of the laser beam, the researchers moved the bubble by as much as 4 µm perpendicular to laser propagation.

They attribute the phenomenon to easily ionized defects at the interface of the void.