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  • richardmitnick 4:59 am on February 20, 2015 Permalink | Reply
    Tags: , , Optics technology   

    From Harvard: “Perfect colors, captured with one ultra-thin lens” 

    Harvard University

    Harvard University

    February 19, 2015
    Caroline Perry, (617) 496-1351

    No need for color correction—Harvard physicists’ flat optics, using nanotechnology, gets it right the first time

    Most lenses are, by definition, curved. After all, they are named for their resemblance to lentils, and a glass lens made flat is just a window with no special powers.
    But a new type of lens created at the Harvard School of Engineering and Applied Sciences (SEAS) turns conventional optics on its head.

    This completely flat, ultrathin lens can focus different wavelengths of light at the same point, achieving instant color correction in one extremely thin, miniaturized device. (Image courtesy of Patrice Genevet, Federico Capasso, and Francesco Aieta, Harvard SEAS.)

    A major leap forward from a prototype device demonstrated in 2012, it is an ultra-thin, completely flat optical component made of a glass substrate and tiny, light-concentrating silicon antennas. Light shining on it bends instantaneously, rather than gradually, while passing through. The bending effects can be designed in advance, by an algorithm, and fine-tuned to fit almost any purpose.

    With this new invention described today in Science, the Harvard research team has overcome an inherent drawback of a wafer-thin lens: light at different wavelengths (i.e., colors) responds to the surface very differently. Until now, this phenomenon has prevented planar optics from being used with broadband light. Now, instead of treating all wavelengths equally, the researchers have devised a flat lens with antennas that compensate for the wavelength differences and produce a consistent effect—for example, deflecting three beams of different colors by the same angle, or focusing those colors on a single spot.

    “What this now means is that complicated effects like color correction, which in a conventional optical system would require light to pass through several thick lenses in sequence, can be achieved in one extremely thin, miniaturized device,” said principal investigator Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at Harvard SEAS.

    Ordinary refractive lenses (left) suffer from significant chromatic aberrations as different wavelengths are focused in different spots. To compensate for this chromatic dispersion, additional lenses have to be added in an objective to compensate for chromatic aberrations as the number of wavelengths to be corrected increases. An achromatic doublet corrects for 2 wavelengths, an apochromat for 3 and finally a so called super-achromat for four wavelengths. The Harvard team’s new metasurface lenses (right) are designed to focus light in the same spot for 3 different wavelengths with no need to increase the lens thickness and footprint. (Image courtesy of Patrice Genevet, Federico Capasso, and Francesco Aieta, Harvard SEAS.)

    Bernard Kress, Principal Optical Architect at Google [X], who was not involved in the research, hailed the advance:

    “Google [X], and especially the Google Glass group, is relying heavily on state-of-the-art optical technologies to develop products that have higher functionalities, are easier to mass produce, have a smaller footprint, and are lighter, without compromising efficiency,” he said. “Last year, we challenged Professor Capasso’s group to work towards a goal which was until now unreachable by flat optics. While there are many ways to design achromatic optics, there was until now no solution to implement a dispersionless flat optical element which at the same time had uniform efficiency and the same diffraction angle for three separate wavelengths. We are very happy that Professor Capasso did accept the challenge, and also were very surprised to learn that his group actually solved that challenge within one year.”

    The team of researchers, led by Capasso and postdoctoral fellow Francesco Aieta, has developed a design that rivals the bulky equipment currently used in photography, astronomy, and microscopy. It could also enable the creation of new miniature optical communications devices and find application in compact cameras and imaging devices.

    The new lens, dubbed an “achromatic metasurface,” dramatically improves on the flat lens Capasso’s research group demonstrated in 2012. That prototype, the first of its kind, corrected for some of the aberrations of conventional lenses but suffered from the limitation of only focusing light of a single wavelength, and its focusing efficiency was small. The new model uses a dielectric material rather than a metal for the nanoantennas, a change which greatly improves its efficiency and, combined with a new design approach, enables operation over a broad range of wavelengths.

    Most significantly, the new design enables the creation of two different flat optical devices. The first, instead of sending different colors in different directions like a conventional grating, deflects three wavelengths of light by exactly the same angle. In the second device, the three wavelengths can all be focused at the same point. A flat lens can thus create a color image—focusing for example red, green, and blue, the primary colors used in most digital displays. The team’s computational simulations also suggest that a similar architecture can be used to create a lens that collimates many different wavelengths, not just three.

    “This is a major step forward in establishing a planar optical technology with a small footprint which overcomes the limitations of standard flat optics, known as diffractive optics,” said Capasso. “It also opens the door to new functionalities because of the enormous design space made possible by metasurfaces.”

    In 2012, the research demonstrated a prototype flat lens that could create a perfectly focused image or a twisting vortex beam. In a major leap forward, announced in February 2015, the researchers have demonstrated that a metasurface can focus different wavelengths of light at the same point, achieving instant color correction in one extremely thin, miniaturized device. Left to right: Francesco Aieta, Federico Capasso, and Patrice Genevet. Not pictured, Mikhail Kats. (File photo by Eliza Grinnell, Harvard SEAS.)

    “This is an elegant and groundbreaking accomplishment,” said Nader Engheta, H. Nedwill Ramsey Professor at the University of Pennsylvania, who was not involved in the research. “The planar optical structures designed and demonstrated by Professor Capasso’s group have much less volume than their conventional bulky counterparts and at the same time their chromatic aberration has been suppressed. This is an important development that will undoubtedly lead to other exciting innovations in the field of flat photonics.”

    Harvard’s Office of Technology Development has filed for a provisional patent on the new optical technology and is actively pursuing commercial opportunities.

    “Our previous work on the metallic flat lens produced a great excitement in regard to the possibility of achieving high numerical aperture and spherical aberration-free focusing with a very compact design. By demonstrating achromatic lenses we have now made a major step forward towards widespread future application of flat optics that will certainly attract the interest of the industry,” said lead author Francesco Aieta, now employed by Hewlett Packard, who conducted the research at Harvard SEAS.

    Additional coauthors of the Science paper include Mikhail A. Kats and Patrice Genevet, both former members of the Capasso laboratory. Kats, who earned his Ph.D. at Harvard SEAS in 2013, is now an assistant professor at the University of Wisconsin, Madison. Genevet, formerly a postdoctoral research associate at SEAS, is now at the Singapore Institute of Manufacturing Technology.

    This research was supported in part by a MURI grant from the Air Force Office of Scientific Research (FA9550-12-1-0389), with additional support from Draper Laboratory (SC001-0000000731), and the National Science Foundation (NSF, ECCS-1347251). Fabrication was performed at the Harvard Center for Nanoscale Systems, which is a member of the NSF-funded National Nanotechnology Infrastructure Network.

    See the full article here.

    Harvard is the oldest institution of higher education in the United States, established in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. It was named after the College’s first benefactor, the young minister John Harvard of Charlestown, who upon his death in 1638 left his library and half his estate to the institution. A statue of John Harvard stands today in front of University Hall in Harvard Yard, and is perhaps the University’s best known landmark.

    Harvard University has 12 degree-granting Schools in addition to the Radcliffe Institute for Advanced Study. The University has grown from nine students with a single master to an enrollment of more than 20,000 degree candidates including undergraduate, graduate, and professional students. There are more than 360,000 living alumni in the U.S. and over 190 other countries.

    Please help promote STEM in your local schools.

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  • richardmitnick 7:50 am on September 11, 2014 Permalink | Reply
    Tags: , , Optics technology   

    From LLNL: “New energy record set for multilayer-coated mirrors” 

    Lawrence Livermore National Laboratory

    Anne M Stark, LLNL, (925) 422-9799, stark8@llnl.gov

    Multilayer-coated mirrors, if used as focusing optics in the soft gamma-ray photon energy range, can enable and advance a range of scientific and technological applications that would benefit from the large improvements in sensitivity and resolution that true imaging provides.

    In a paper published in a recent online edition of Optics Express, LLNL postdoc Nicolai Brejnholt and colleagues from LLNL, the Technical University of Denmark and the European Synchrotron Radiation Facility demonstrate for the first time that very short-period multilayer coatings deposited on super-polished substrates operate efficiently as reflective optics above 0.6 MeV, nearly a factor of two higher than the previous record at 384 keV, set last year by this same group (Physical Review Letters 101 027404, 2013).

    Regina Soufli, Marie-Anne Descalle, postdoc Nicolai Brejnholt (shown in photo) and LLNL colleagues and collaborators recently demonstrated that very short-period multilayer coatings deposited on super-polished substrates operate efficiently as reflective optics.

    Multilayer mirrors can be used for two broad classes of applications. First, they can be used in spectroscopy, to enhance or suppress certain photon. energies. The team is looking into how to use multilayers to examine spent nuclear fuel for non-proliferation missions.

    Second, multilayer mirrors can be used as focusing, imaging optics by applying multilayer coatings to curved substrates. “We have previously made hard X-ray optics for nuclear medicine and astrophysics applications, and we can now consider adapting the same fabrication techniques to work in the soft gamma-ray band,” said Michael Pivovaroff, LLNL co-author.

    The field of astrophysics would benefit the most from gamma-ray focusing optics, including the sub-disciplines of galactic and extragalactic astronomy, solar astronomy, cosmic-ray research and potentially observational cosmology. Gamma-ray optics also have shown promise for nuclear medicine and nuclear non-proliferation applications.

    “We have demonstrated the capability to make highly reflective multilayer thin films with ultra-short period thickness (1-2 nanometers) and stable, ultra-smooth interfaces between the layers, as needed for operation at these extremely high photon energies. We chose tungsten carbide/silicon carbide (WC/SiC) multilayers for this purpose,” said Regina Soufli, another LLNL co-author.

    “The measurements at 0.65 MeV showed we had to understand sub-nanometer variations across the 36-square-inch mirror to model the measured performance,” Brejnholt said.

    The team demonstrated that multilayer mirrors in the gamma-ray band operate efficiently and according to well-understood models. The team combined classical, wave interference models with a Monte-Carlo particle simulation code. The latter was used to account for incoherent scattering, a phenomenon that is negligible at lower photon energies but becomes significant in the soft gamma ray range. Incoherent scattering was observed and modeled on multilayer structures for the first time by the LLNL team.

    Other Livermore co-authors include Marie-Anne Descalle, principal investigator of the Laboratory Directed Research and Development (LDRD) project that funded this effort, Mónica Fernández-Perea, Jennifer Alameda, Tom McCarville and Sherry Baker.

    See the full article here.

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  • richardmitnick 5:54 pm on December 6, 2012 Permalink | Reply
    Tags: , , , Optics technology, ,   

    From Brookhaven: “Growing Cutting-edge X-ray Optics” 

    Brookhaven Lab

    Scientists use a custom-designed machine and a reprogrammed Xbox controller to create atomically precise lenses

    December 6, 2012
    Justin Eure

    Unleashing some of the most promising energy technologies of tomorrow—from electric vehicle fuel cells to photovoltaics—hinges upon understanding tiny structures spanning just billionths of a meter. One way to explore this critical nanoscale world is by sending high-intensity x-ray beams through materials, similar to the way doctors capture images of internal bone structure using large x-ray devices. The challenge with fringe physics, however, is that focusing that penetrating power on just a single nanometer takes an entirely different caliber of lens.…”

    See how it is done-

    Is that cool, or what?

    “Using a massive, custom-built deposition device, Brookhaven Lab scientist Ray Conley and his team are able to grow special lenses one atomic layer at a time. As intense x-rays pass through these multilayer Laue lenses (MLL), the light diffracts and bends toward a single point. Creating these atomically precise optics is no small feat, and Conley continues to tweak the process of growing light-bending films and carving them into precise lenses.”

    See the full article here.

    The completed MLLs will be deployed on beamlines at Brookhaven Lab’s forthcoming National Synchrotron Light Source II, one of the world’s most advanced light sources, to reveal unparalleled details of nanomaterial structures.

    Brookhaven’s current light source — the National Synchrotron Light Source (NSLS) — is one of the world’s most widely used scientific facilities. Each year, 2,200 researchers from 400 universities, government laboratories, and companies use its bright beams of x-rays, ultraviolet light, and infrared light for research in such fields as biology, medicine, chemistry, environmental sciences, physics, and materials science. The scientific productivity of the NSLS user community is very high and has widespread impact, with more than 900 publications per year, many in premier scientific journals.

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

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