Light
can creep through tiny holes in a metal plate, even
if those holes are smaller in diameter than the wavelength
of light. What’s more, the light is stored for a short
period of time on the metal surface, as if the metal
were a photonic crystal. The controlled interaction
of light with such metal structures could pave the
way to unique methods for nanosensing or nanoscale
information transfer, write Claus Ropers and colleagues
in the forthcoming issue of Physical Review Letters
(“Femtosecond light transmission and subradiant damping
in plasmonic crystals”).
In
their experiments conducted at the Max Born Institute
in Berlin, Ropers and colleagues aim an ultrashort
laser pulse at a nanostructured metal surface. The
initial laser pulse measures 10 femtoseconds (fs).
1 fs is the millionth part of a billionth second (0.000000000000001
second). As the light hits the surface, it drives
electron oscillations and generates surface-bound
electromagnetic waves, known as surface plasmon polaritons.
These
surface plasmon polaritons cause an unusually high
transmission through sub-wavelength apertures, i.e.
the tiny holes, or travel along nanometric waveguides.
These phenomena evolve on an extremely short time
scale and have so far refrained from any direct time-resolved
observation. Now, researchers at the Max-Born-Institute
in Berlin, Germany and at Seoul National University
in Korea, report on a new experiment to measure the
polariton lifetime by tracking amplitude and phase
of extremely short, 10-fs laser pulses while they
are transmitted through a plasmonic crystal, a periodic
array of nanometer-sized slits in a thin metal film
(Fig. 1). They find lifetimes reaching up to 300 fs,
more than an order of magnitude larger than previously
thought.
This
surprising finding can be tracked down to the microscopic
spatial structure of the plasmon field (Fig. 2), which
displays symmetric (cosine-like) and antisymmetric
(sine-like) plasmon modes, depending on excitation
wavelength. The latter display a strongly reduced
overlap with the nanoslit scattering centers, which
inhibits the emission of electromagnetic radiation
and therefore reduces radiative damping of the plasmon
field.
These
experiments devise a way to control surface plasmon
radiation by tailoring their spatial mode profiles,
an important prerequisite for using plasmonic crystals
in nanosensing, or waveguiding applications or even
as flying qubits in quantum information processing.
For
more information please contact:
Dr. Christoph Lienau
Max-Born-Institut für Nichtlineare Optik und
Kurzzeitspektroskopie
Max-Born-Str 2A
D-12489 Berlin
Phone: +49-30-6392-1476
Mail: lienau@mbi-berlin.de
