The chip, etched with a series of steps in a pattern resembling a spiral staircase, is the brainchild of Grover Swartzlander of the University of Arizona's College of Optical Sciences.

"Some people say that I study darkness, not optics," Swartzlander said, adding that his devices also could be useful to optical microscopy, and could protect cameras and imaging systems from glare.

The chips work by redirecting light waves. When light hits them dead on, they slow it down more in the thicker layers than in the thinner ones. Eventually, the chips split the light and phase-shift it so some light waves move 180 degrees out of phase with others. The light spins through the chip like wind in a hurricane, until light waves that are 180 degrees out of phase cancel out one another, leaving a totally dark central core.

Swartzlander said it is somewhat like light following the threads of a bolt, but the pitch of the 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. Mathematically, it's beautiful."

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

Swartzlander and his graduate students Gregory Foo and David Palacios published an article in Optics Letters recently on how optical vortex masks might be used on powerful telescopes. The masks could be used to block starlight and allow astronomers to directly detect light from planets that are 10-billion-times dimmer than the star they orbit.

This could be done with a device called an optical vortex coronagraph. Traditional coronagraphs use an opaque disk to block a star's light, but astronomers searching for faint planets near bright stars can't use them, because glare from starlight diffracts around the disk, thereby obscuring any light reflected from a planet.

"Any small amount of diffracted light from the star is still going to overwhelm the signal from the planet," Swartzlander said, "but if the spiral of the vortex mask coincides exactly with the center of the star, the mask creates a black hole where there is no scattered light, and you'd see any planet off to the side."

The research team, which included Eric Christensen from UA's Lunar and Planetary Lab, demonstrated a prototype optical vortex coronagraph on Steward Observatory's 60-inch Mount Lemmon telescope two years ago. They couldn't search for planets outside the solar system, because the telescope was not equipped with adaptive optics to correct for atmospheric distortions.

Instead, the team took pictures of Saturn and its rings to demonstrate how easily such a mask could be used with a telescope's existing camera system.

Swartzlander said optical vortex coronagraphs could be valuable to future space telescopes, such as NASA's Terrestrial Planet Finder and the European Space Agency's Darwin mission. The TPF mission - which currently is stalled because of budget restrictions - will use an array of space-based telescopes to measure the size, temperature and placement of planets as small as Earth in the habitable areas of distant solar systems.

"We're applying for grants to make a better mask to really ramp this thing up to get better quality optics, Swartzlander said. "We can demonstrate this now in the lab for laser beams, but we need a really good-quality mask to get closer to what's needed for a telescope."

The big challenge is developing a way to etch the mask to get "a big fat zero of light" at its core, he said.

The team is conducting numerical simulations to determine the proper pitch for helical masks at the desired optical wavelengths, and Swartzlander said he has filed a patent for a mask that covers more than one wavelength of light.

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