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A kitchen gadget used to sift flour and other ingredients is theinspiration behind the name of an emerging technology that couldresolve some of the more intriguing components of the sun'schromosphere - the irregular layer above the photosphere thatcontributes to the formation of solar flares and coronal massejections. Adrian Daw and Douglas Rabin, scientists at NASA's Goddard SpaceFlight Center in Greenbelt, Md., are collaborating with researchersat the U.S. Air Force Academy (USAFA) in Colorado and other AirForce-affiliated organizations to build a small solar observatoryequipped with the so-called "photon sieve," an eight-inch(20-centimeter) diffractive optic. A version of this technology was successfully demonstrated in aground test, paving the way for its flight on a tiny Cubesatsatellite in 2014 - the Air Force-sponsored FalconSat-7 mission.That mission will demonstrate the practicality of deploying thisemerging technology in space and possibly paving the way for alarger heliophysics mission in the future. "We've studied the sun's corona for years and it's complicated. Butthe chromosphere, which can be seen as a thin pink layer during atotal solar eclipse, is even harder to understand," Daw said."Things are happening there at spatial scales we can't currentlyresolve with existing space- or ground-based telescopes." Although a large observatory comparable in size to the Hubble SpaceTelescope could resolve currently unseen magnetic flux tubes andfilamentary plasma within coronal loops, the cost to build aconventional large-aperture solar telescope is prohibitive, Dawsaid. "The photon sieve could help us overcome this obstacle and help usprovide a game-changing technology for high-resolution imaging inspace," he said. A Variant of Fresnel Zone Plates The technology that could help bring these details to light is avariant of the Fresnel zone plate, which focuses light throughdiffraction rather than refraction or reflection. These devicesconsist of a set of alternating transparent and opaque concentriccircular rings. Light hitting the plate diffracts around the opaque zones, whichare precisely spaced so that the diffracted light interferes at thedesired focus to create an image taken by a camera. The sieve operates largely the same. However, the rings are dottedwith millions of holes, like a kitchen sieve or sifter, whose sizesand positions are configured so that the light diffracts to adesired focus. As a result of its design, the sieve can be patterned on a flatsurface and can be easily scaled up in size - particularly ifconstructed of a polyimide film similar to the ubiquitous Kapton,which spacecraft and instrument developers commonly use because itcan withstand extreme temperatures and vibration. But perhaps the most significant advantage is that the lightweight,easily rolled and deployed film need not be pulled to a perfectoptical flatness like more traditional mirrors. In fact, surfacerequirements for traditional mirrors are 100 times more stringent -making the photon sieve ideal as a quick-turnaround space-basedoptic. This appeals to the Air Force. In the event of a catastrophic lossof its current intelligence, surveillance, and reconnaissancesatellites, the military would need a simple replacement systemeasily deployed from a small, inexpensive satellite, like aCubesat. Since its invention more than a decade ago by Lutz Kipp, aprofessor at Kiel University in Germany, researchers at the USAFA'sLaser and Optics Research Center have experimented with differentmaterials for making the sieve. USAFA's Geoff Andersen, MichaelDearborn, and Geoff McHarg initially experimented withchrome-coated quartz or glass, later focusing their efforts onlightweight polyimide films or membranes. In laboratory testing, these sieves showed great promise for narrowand broadband imaging in visible wavelength bands, particularly inthe H-alpha wavelength band ideal for detecting structure withinthe solar chromosphere. What they lacked, however, was expertise in solar physics and someof the analytical tools needed to evaluate the sieve's deploymentmechanisms. "They were looking for the best way to demonstratetheir technology," Daw said. "It's easier to test imaging technologies with a really brightsource, like the sun. They contacted us to see if we wanted tocollaborate. Of course we did. The collaboration is proving to beof great mutual benefit to both organizations." Goddard's Contribution to FalconSat-7 Since joining the effort, which also involves the Air ForceResearch Laboratory and the Air Force Institute of Technology, bothlocated at the Wright-Patterson Air Force Base in Ohio, Goddard hasanalyzed requirements for deploying the sieve and keeping themembrane relatively flat once the Cubesat reaches its 280-mile(450-kilometer) orbit. Daw's team also designed and constructed a ground-based imagingsystem to test a glass version of the sieve. "Using this system, wetook the first-ever solar images using such a device," Daw said."In fact, these are the first images of any astronomical objectusing a photon sieve." The next step is carrying out ground-basedtests of the membrane sieve, he added. "These two accomplishments - a ground-based demonstration of thephoton-sieve technology and the analysis of the deployment system -are major advances for deployable membrane optics," Daw said. As aresult of these successes, he and his team are now investigatingways to extend the sieve's wavelength range to the extremeultraviolet, which is most interesting to solar physicists. "Thistechnology has lots of applications for heliophysics," Daw said. The e-commerce company in China offers quality products such as Car Mobile DVR , China IR Waterproof Camera, and more. For more , please visit GPS Mobile DVR today!
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