| FEATURES & INNOVATIONS |


A revolution


in light at the small scale


Surprising optical effects in semiconductor nanoparticles promise to realize the latent potential of nanophotonics


L


ight behaves in rather tame and predictable ways when interacting with everyday objects — it travels in straight lines, rebounds when it hits shiny surfaces, and gets bent by lenses. But


weird and wonderful things start to happen when light interacts with very small objects. Nanoparticles, for example, which are collec- tions of atoms as small as a virus, can act as mini-antennas, and small disks of silicon can set off strange ‘modes’ of light that render the disks invisible. A new area of optics has emerged in recent


years to study these strange phenomena. “Nanophotonics, a branch of optics dealing with light at nanoscale dimensions, has become a hot research topic over the last decade or so,” notes Arseniy Kuznetsov of the A*STAR Data Storage Institute. “It holds a lot of promise for various new applications, ranging from high-speed information transmission and holographic display technologies to bioimaging and genome sequencing.” Kuznetsov’s team is leading devel- opments in a subfield of nanophotonics, which could ensure its widespread practical application.


Light on tiny scales Traditionally, nanophotonics has focused on tiny metal structures such as gold and silver


42 A*STAR RESEARCH


nanoparticles. Light’s oscillating electric field causes the free electrons in metals to oscillate collectively. At certain particle sizes, this can give rise to an effect known as surface plasmon resonance. Resonance is a general phenomenon in which a system exhibits a much larger response at certain frequencies — for example, an opera singer can cause a wine glass to shatter by singing at the pitch that it resonates at. Surface plasmon resonance refers to the specific resonance effect produced by surface plasmons, which are a collection of charged oscillations — the study of which is known as nanoplasmonics. While a very new research area, nanoplasmonic effects have been exploited for centuries — stained-glass windows in medieval cathedrals owe their color to surface plasmons excited in metal nanoparticles embedded in the glass. Despite the high expectations for


nanoplasmonics in areas such as information technology, security, energy, high-density data storage and the life sciences, it has resulted in relatively few practical applications. One reason for this disappointing outcome is that metal nanostructures lose a lot of light to absorption. “A deeper understanding of these resonances has brought a general understanding of major drawbacks related to unavoidable high losses in


ISSUE 6 | JANUARY – MARCH 2017


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