posted on 2018-09-11, 00:00authored byXiaojun Liu, Xiaomeng Jia, Martin Fischer, Zhiqin Huang, David R. Smith
Light
switchable materials are essential to optoelectronic applications
in photovoltaics, memories, sensors, and communications. Natural switchable
materials suffer from weak absorption and slow response times, preventing
their use in low-power, ultrafast applications. Integrating light
switchable materials with metasurface perfect absorbers offers an
innovative route to achieving desirable features for nanophotonic
devices, such as directional emission, low-power and broadband operation,
high radiative quantum efficiency, and large spontaneous emission
rates. Here we show an enhanced two-photon photochromism based on
a metasurface perfect absorber: film-coupled colloidal silver nanocubes.
The photochromic molecules, spiropyrans, are sandwiched between the
silver nanocubes and the gold substrate. With nearly 100% absorption
and an accompanying large field enhancement in the molecular junction,
the transformation of spiropyrans to merocyanines is observed under
excitation with 792 nm laser light. Fluorescence lifetime measurements
on the merocyanine form reveal that large Purcell enhancement in the
film-coupled nanocubes leads to large enhancements of the spontaneous
emission rate and a high quantum efficiency. An averaged incident
power as low as 10 μW is enough to initiate the two-photon isomerization
of spiropyran in the film-coupled nanocubes, and a power of 100nW
is able to excite the merocyanines to emit fluorescence. The power
consumption is orders of magnitude lower than bare spiropyran thin
films on silicon and gold, which is highly desirable for the writing
and reading processes relevant to optical data storage. By sweeping
the plasmonic resonance of the film-coupled nanocubes, wavelength
specificity is demonstrated, which opens up new possibilities for
minimizing the cross talk between adjacent bits in nanophotonic devices.