|
Posted by Andrew Yee on February 27, 2006, 6:11 pm
Please log in for more thread options
University Communications
University of Arizona
Tucson, Arizona
Contact Information:
Grover Swartzlander, 520-626-3723
February 28, 2006
Optical Device Cancels Starlight So Astronomers Can See Distant Planets
By Lori Stiles
"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.
Swartzlander and his graduate students, Gregory Foo and David Palacios,
garnered media attention recently when "Optics Letters" published their
article 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 a 10-billion-times-dimmer planet orbiting the
star.
This could be done with an "optical vortex coronagraph." In a traditional
coronagraph, an opaque disk is used to block a star's light. But
astronomers who are searching for faint planets near bright stars can't
use the traditional coronagraph because glare from starlight diffracts
around the disk obscuring light reflected from the planet.
"Any small amount of diffracted light from the star is still going to
overwhelm the signal from the planet," Swartzlander explained. "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 UA team, which also 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 our solar system because the 60-inch
telescope isn't equipped with adaptive optics that corrects for
atmospheric turbulence.
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. A photo from the test is online at Swartzlander's website,
http://www.u.arizona.edu/~grovers
Optical vortex coronagraphs could be valuable to future space telescopes,
such as NASA's Terrestrial Planet Finder (TPF) and the European Space
Agency's Darwin mission, Swartzlander noted. The TPF mission will use
space-based telescopes to measure the size, temperature, and placement of
planets as small as the 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.
Swartzlander and his graduate students are doing numerical simulations to
determine the proper pitch for helical masks at the desired optical
wavelengths. Swartzlander has filed a patent for a mask that covers more
than one wavelength, or color of light.
The U.S. Army Research Office and State of Arizona Proposition 301 funds
support this research.
The Army Research Office funds basic optical sciences research, although
Swartzlander's work also has practical defense applications.
Optical vortex masks also could be used in microscopy to enhance the
contrast between biological tissues.
[NOTE: Images supporting this release are available at
http://uanews.org/cgi-bin/WebObjects/UANews.woa/9/wa/SciDetails?ArticleID=12320 ]
|
| Similar Threads | Posted | | Astronomers find most stable optical clock in the heavens (Forwarded) | December 1, 2005, 1:23 pm |
| Astronomers Claim to Find the Most Distant Known Galaxies (Forwarded) | July 10, 2007, 5:12 pm |
| Astronomers Seize Rare Opportunity to Measure Distant Charon(Forwarded) | January 4, 2006, 7:03 pm |
| Astronomers find the most distant star clusters hidden behind a nearby cluster (Forwarded) | January 11, 2007, 7:06 pm |
| When Worlds Collide: Have Astronomers Observed the Aftermath of a Distant Planetary Collision? (Forwarded) | January 10, 2008, 6:00 pm |
| Hobby-Eberly Telescope Helps Astronomers Learn Secrets of One of Universe's Most Distant Objects (Forwarded) | June 11, 2007, 10:43 pm |
| European Astronomers set sights on Earth-like planets and the firststarlight (Forwarded) | July 25, 2005, 3:02 pm |
| Astronomers Find Stellar Cradle Where Planets Form | November 29, 2007, 5:21 pm |
| Astronomers Discover Dusty Remains of Two Terrestrial Planets | October 3, 2008, 6:17 pm |
| Astronomers Debate Whether Oldest Known Dust Disk Will Ever Form Planets | July 18, 2005, 6:08 pm |
|
XML Sitemap