{"id":2180,"date":"2023-07-05T11:33:03","date_gmt":"2023-07-05T11:33:03","guid":{"rendered":"https:\/\/thisbiginfluence.com\/?p=2180"},"modified":"2023-07-05T11:33:03","modified_gmt":"2023-07-05T11:33:03","slug":"harvard-scientists-control-points-of-darkness-for-remote-sensing-and-covert-detection-applications","status":"publish","type":"post","link":"https:\/\/thisbiginfluence.com\/?p=2180","title":{"rendered":"Harvard Scientists Control \u201cPoints of Darkness\u201d for Remote Sensing and Covert Detection Applications"},"content":{"rendered":"


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By<\/span> Kat J. McAlpine, Harvard John A. Paulson Faculty of Engineering and Utilized Sciences<\/span>
\nJuly 5, 2023<\/span><\/p>\n

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\"Metasurface<\/a><\/p>\n

Harvard researchers have developed methods to regulate \u201cfactors of darkness\u201d in gentle utilizing metasurfaces, opening up new potentialities in fields like distant sensing, precision measurement, and covert detection. The group created exact darkish spots that may seize atoms or act as measurement factors for imaging, and developed resilient \u201cpolarization singularities,\u201d secure darkish spots in polarized optical fields. This can be a scanning electron microscope picture of the metasurface that generated the purpose singularities. Credit score: Harvard College<\/p>\n

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Two research report new strategies for utilizing metasurfaces to create and management darkish areas referred to as \u201coptical singularities.\u201d<\/strong><\/p>\n

Optical units and supplies enable scientists and engineers to harness gentle for analysis and real-world purposes, like sensing and microscopy. Federico Capasso\u2019s group on the Harvard John A. Paulson Faculty of Engineering Utilized Sciences (SEAS) has devoted years to inventing extra highly effective and complicated optical strategies and instruments. Now, his group has developed new methods to exert management over factors of darkness, slightly than gentle, utilizing metasurfaces.<\/p>\n

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\u201cDarkish areas in electromagnetic fields, or optical singularities, have historically posed a problem because of their complicated constructions and the issue in shaping and sculpting them. These singularities, nonetheless, carry the potential for groundbreaking purposes in fields resembling distant sensing and precision measurement,\u201d stated Capasso, the Robert L. Wallace Professor of Utilized Physics and Vinton Hayes Senior Analysis Fellow in Electrical Engineering at SEAS and senior corresponding creator on two new papers describing the work.<\/p>\n

\"Experimental<\/a><\/p>\n

Experimental depth profiles, with the purpose singularities labeled. Credit score: Harvard College<\/p>\n

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<\/span>In 2011, Capasso\u2019s lab launched metasurfaces, or sub-wavelength-spaced arrays of nanostructures. In 2016, they used metasurfaces to construct high-performance metalenses \u2013 flat optical lenses comprising nanopillars that they fabricated utilizing semiconductor lithography methods \u2013 which unlocked a brand new technique to focus gentle utilizing extraordinarily light-weight units.<\/p>\n

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The most recent research from the Capasso group \u2013 revealed in Nature Communications<\/span><\/em> and Science Advances<\/span><\/em> \u2013 report how metasurface technology can harness not just light, but also darkness.<\/p>\n

\u201cBoth of these studies introduce new classes of optical singularities \u2013 regions of designed darkness \u2013 using powerful but intuitive algorithms to inform the fabrication of metasurfaces,\u201d said Soon Wei Daniel Lim, co-first author of the paper in Nature Communications <\/em>with Joon-Suh Park.<\/p>\n

In that study, Lim and collaborators designed and fabricated an optical device containing metasurfaces of titanium dioxide nanopillars that can control light to create an array of optical singularities.<\/p>\n

To control exactly where these points of darkness appear, Lim used a computer algorithm to help him reverse engineer the design of the metasurface.<\/span><\/p>\n

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\u201cI told the computer: Here\u2019s what I want to achieve in terms of dark spots, tell me what shape and diameter the nanopillars should be on this metasurface to make this happen,\u201d he said.<\/p>\n

As light travels through the metasurface and lens, it generates a prescribed array of dark spots.<\/p>\n

\u201cThese dark spots are exciting because they could be used as optical traps to capture atoms,\u201d Lim said. \u201cIt\u2019s possible this could be used to simplify the optical architecture used in atomic physics labs, replacing today\u2019s conventional equipment \u2013 instruments that take up 30 feet of space on a lab table \u2013 with compact, lightweight optical devices.\u201d<\/p>\n

Dark spots aren\u2019t just handy for trapping atoms. They can also be useful as highly precise reference positions for imaging.<\/p>\n

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\u201cPoints of darkness are much smaller than points of light,\u201d Lim said. \u201cAs part of an imaging system, that makes them effective points of measurement to accurately discriminate between two different positions within a sample.\u201d<\/p>\n

In their Science Advances <\/em>paper, the Capasso group described a new class of optical singularities: extremely stable points of darkness in a polarized optical field, known as polarization singularities.<\/p>\n

\u201cWe\u2019ve designed points of darkness that can withstand a wide range of perturbations \u2014 they are topologically protected,\u201d said Christina Spaegele, first author of the paper. \u201cThis robustness opens the way to optical devices with high reliability and durability in various applications.\u201d<\/p>\n

Previous research achieved some polarization singularities, but the conditions for maintaining that perfect spot of darkness were extremely fragile, making them easily destroyed by stray light or other environmental conditions.<\/p>\n

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\u201cBy shining light through a specially-designed metasurface and focusing lens, we can produce an unwavering polarization singularity surrounded entirely by points of light \u2013 essentially creating a dark spot inside a sphere of brightness,\u201d Spaegele said.<\/p>\n

The technique is so robust that even introducing a defect to the metasurface doesn\u2019t destroy the dark spot, but simply shifts its position.<\/p>\n

\u201cThis degree of control could be especially useful for imaging samples in \u2018hostile\u2019 environments, where vibrations, pressure, temperature, and stray light would typically interfere with imaging behavior,\u201d Spaegele said.<\/p>\n

The team says these new developments in optical singularities have implications for remote sensing and covert detection.<\/p>\n

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\u201cPoints of darkness could be used to mask out bright sources while imaging a scene, allowing us to see faint objects that are otherwise overshadowed,\u201d Capasso said. \u201cObjects or detectors placed at these dark positions will also not give away their position by scattering light, allowing them to be \u2018hidden\u2019 without affecting the surrounding light.\u201d<\/p>\n

References:<\/p>\n

\u201cPoint singularity array with metasurfaces\u201d by Soon Wei Daniel Lim, Joon-Suh Park, Dmitry Kazakov, Christina M. Sp\u00e4gele, Ahmed H. Dorrah, Maryna L. Meretska and Federico Capasso, 5 June 2023, Nature Communications<\/em>.
DOI: 10.1038\/s41467-023-39072-6<\/a><\/p>\n

\u201cTopologically protected optical polarization singularities in four-dimensional space\u201d by Christina M. Spaegele, Michele Tamagnone, Soon Wei Daniel Lim, Marcus Ossiander, Maryna L. Meretska and Federico Capasso, 16 June 2023, Science<\/em>.
DOI: 10.1126\/sciadv.adh0369<\/a><\/p>\n

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Harvard\u2019s Office of Technology Development has protected the intellectual property arising from these studies and is exploring commercialization opportunities.<\/p>\n

Additional authors who contributed to these papers include Dmitry Kazakov, Ahmed H. Dorrah, Maryna L. Meterska, Michele Tamagnone, and Marcus Ossiander.<\/p>\n

This research was supported by the Air Force Office of Scientific Research and the European Research Council.<\/p>\n

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