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A*STAR Signapore - Plasmonics - A wave without diffraction

DCN Corp® - When laser light hits grooves in a thin film of Gold (Au) (left), it generates surface plasmon polariton waves (cyan dashed lines) that converge and interfere to create a non-diffracting beam (orange).  Credit - Patrice Genevet - © 2013 Harvard UniversityBold claim by A*STAR Singapore researchers that optical computing could benefit from the development of a novel electromagnetic wave

An unconventional wave which does not spread-out as it travels could inadvertently become a key component in speedy computer chips, which employ beams of light to carry/process data.  Jiao Lin, a physicist at the A*STAR Singapore Institute of Manufacturing Technology - assisted in developing the electromagnetic wave, which can travel some 80 micro-meter in a straight line with diffracting. [1]

Essentially the wave forms when light/laser hits the surface of a metal, and thereafter creating ripples in the sea of electrons. Interestingly under certain condition, the ripples - typically known as surface plasmons - couple with the incoming light to create electromagnetic waves that tightly attach to the metal surface as they travel.  Also, known as surface plasmon polaritons, such waves have a shorter wavelength than the light, which make them more positive as data carriers.

Though light can easily zip around a computer, which is much faster than electrons - optical components tend to be much larger than those in conventional circuits, whereby their size is dictated by the wavelength of the light they handle.  Employing surface plasmons polaritons offers the best of both worlds - states Lin, primarily because the signals can travel at the speed of light along metal wave-guides, that are as compact a conventional circuits.  Negatively, surface plasmon polaritons diffract as they travel over the metal, which erodes the quality of the signal they carry.  Attempts to prevent this diffraction were relatively successful, but caused the polaritons to veer off course.

The wave developed by Lin and co-workers is a previously unknown solution to Maxwell's equations, which describe how electromagnetic fields behave.  Once the research team had formulated a mathematical description of this wave, known as a localised cosine-Gauss beam, Lin helped to turn it into reality.  The team carved two sets of tiny grooves, each roughly 10 micrometers long, into a thin layer of Gold (Au) stuck to a glass backplate.  The grooves were slightly angled to make a chevron pattern (see above image).

Directing near-infrared (NIR) laser light at the grooves generated two surface plasmon polaritons, which soon converged and interfered constructively with each other.  Resulting in a focused beam that skimmed across the Au without diffracting, covering a much greater distance than previous efforts had achieved.  The team tracked the narrow beam as it traveled over the surface using a near-field scanning optical microscope.  Lin concludes in stating that as well as helping to create faster and more energy efficient computers - the beams could also be used in the laboratory to trap/manipulate nanoparticles.  Original article available here

Excitingly DCN Corp finds the above research highly intutive, and wishes to find-out if the same surface plasmon nanoparticle thin film performance can be achieved from the company's homogeneous dip coating displacement protocol?  If so, and you or your colleagues are interested in making the above a reality - please ensure to contact the company as soon as practicably possible.

[1] Lin, J., Dellinger, J., Genevet, P., Cluzel, B., de Fornel, F. and Capasso, F. - Cosine-Gauss plasmon beam: A localized long-range non-diffracting surface wave. Physical Review Letters 109, 093904 (2012).  Journal citation available here