Lasers Probe Secrets of Superfluids

Seeking to better understand the unusual properties of superfluids, researchers at Princeton University in New Jersey have devised an all-optical model that simulates the properties of these frictionless materials. Superfluid research has applications in sensor technology, atomic trapping and optical communications.

The dispersive shock waves of superfluids have been difficult to study and, therefore, analysis has been limited. The researchers, led by Jason W. Fleischer, assistant professor of electrical engineering, noted that light waves passing through nonlinear crystals and superfluids have comparable qualities: The collective motion of superfluid particles looks like the coherent waves in laser light. In the January issue of Nature Physics, they reported that this well-known, but little appreciated, similarity allowed easier and improved observations of superfluid-like and related dispersive phenomena.

In a substitution experiment, the investigators used light from a Coherent Inc. 532-nm laser split by a Mach-Zehnder interferometer. A lens placed in one arm focused the beam into an 8 × 8 × 8-mm strontium barium niobate photorefractive crystal, while the other beam served as a reference background. They applied a constant voltage of –500 V, creating a self-defocusing nonlinearity. Light exiting the crystal was imaged into a CCD camera from Uniq Vision Inc. The setup enabled the researchers to study the dynamics of dispersive shock waves, including the interaction of colliding waves.