Optical Device Cancels Starlight So Astronomers Can See Distant Planets

"Some people say that I study darkness, not optics," jokes Grover Swartzlander.

But it's a kind of darkness that will allow astronomers to see the light.

Swartzlander, an associate professor in The University of Arizona College of Optical Sciences, is developing devices that block out dazzling starlight, allowing astronomers to study planets in nearby solar systems.

The devices also may prove valuable to optical microscopy and be used to protect camera and imaging systems from glare.

The core of this technology is an "optical vortex mask" -- a thin, tiny, transparent glass chip that is etched with a series of steps in a pattern similar to a spiral staircase.

When light hits the mask dead on, it slows down more in the thicker layers than in thinner ones. Eventually, the light is split and phase shifted so some waves are 180 degrees out of phase with others. The light spins through the mask like wind in a hurricane. When it reaches the "eye" of this optical twister, light waves that are 180 degrees out of phase cancel one another, leaving a totally dark central core.

Swartzlander says this is like light following the threads of a bolt. The pitch of the optical "bolt" -- the distance between two adjacent threads -- is critical. "We're creating something special where the pitch should correspond to a change in the phase of one wavelength of light," he explained. "What we want is a mask that essentially cuts this plane, or sheet, of incoming light and curls it up into a continuous helical beam."

"What we've found recently is knock-your-socks-off amazing from a theoretical point of view," he added.

"Mathematically, it's beautiful."

Optical vortices are not a new idea, Swartzlander noted. But it wasn't until the mid 1990s that scientists were able to study the physics behind it. That's when advances in computer-generated holograms and high-precision lithography made such research possible.