5 Coherent Nonlinear Processes in Metal-Semiconductor …
105
Even though the optical properties of SPPs have been studied for many years,
there has been an upsurge of new interest in active plasmonics, dealing with metalsemiconductor hybrid structures during the last decade. Particularly, light-matter
interaction between SPPs and quantum emitters like excitons in semiconductors has
become an active topic of research [8, 14, 30]. Plasmonic fields can be tailored
with sub-optical wavelength resolution offering promising scenarios for trapping,
guiding and manipulating quantum emitters in dipole potentials, even potentially
enabling strong coupling between a single emitter and a single SPP. Such hybrid
systems connect two fundamentally different quantum worlds of electromagnetic
fields and emitters and open up new opportunities for exploring intriguing lightmatter interactions like Purcell effect, vacuum Rabi splitting and the optical Stark
effect on nanoscale. Recently, coupling strengths of as high as 350 meV have been
observed in metal-semiconductor hybrid nanostructures [8, 14, 24]. Therefore, it is
possible to observe light-matter interaction in these hybrid nanostructures even at
room temperature without any need for a closed cavity. One of the central goals for
hybrid systems is to control light via light by efficiently generating non-classical
entangled states of light and matter. Fundamentally new types of all-optical devices,
e.g. quantum gates and single-photon transistors have been already envisaged based
on coherent nonlinearity in these hybrid structures. Another related unexplored field
is the ability of strong coupling to modify the electromagnetic environment of an
emitter to modify potential energy landscapes and to control chemical reactions.
SPPs can also extend energy transfer range between two emitters, which otherwise
is only a few nm, To-date there appears to be no reports of how this resonant energy
transfer is modified in presence of coherent effects like strong coupling [8, 9, 14].
Here, we discuss the linear and nonlinear optical response of a metalsemiconductor hybrid nanostructures comprising a layer of J-aggregated dye
molecules in close proximity of a nano-slit array in a gold film schematically shown in
Fig. 5.1a. The hybrid nanostructures consist of a ∼ 50 nm thick J-aggregated cyanine
dye (2,2’dimethyl-8-phenyl-5,6,5’,6’-dibenzothiacarbocyanine chloride, Hayashibara Biochemicals Laboratories, Inc.) layer spin-coated onto a periodic nano-groove
array with 380–460 nm period in a gold film [8, 9, 14, 19, 20, 23, 25–27]. This system exhibits strong exciton-SPP coupling at room temperature hence is a potential
candidate to explore coherent nonlinear response in such hybrid structures. We start
by reviewing the linear optical response followed by few examples of experiments to
investigate coherent nonlinearity. Since the system under consideration consists of an
ensemble of molecules interacting with multiple SPP bands, the system behaves as
a collection of classical oscillators. Hence the photon number (intensity) dependent
Rabi frequency discussed earlier is not expected [8, 9, 14]. Nevertheless, as we shall
see in the following sections, the system offers unique possibility to control the Rabi
frequency as a function of pump intensity. Similar studies on how quantum emitters
and SPPs interact in hybrid structures may lead to advances in several directions and
will certainly unravel intriguing phenomena.
105
Even though the optical properties of SPPs have been studied for many years,
there has been an upsurge of new interest in active plasmonics, dealing with metalsemiconductor hybrid structures during the last decade. Particularly, light-matter
interaction between SPPs and quantum emitters like excitons in semiconductors has
become an active topic of research [8, 14, 30]. Plasmonic fields can be tailored
with sub-optical wavelength resolution offering promising scenarios for trapping,
guiding and manipulating quantum emitters in dipole potentials, even potentially
enabling strong coupling between a single emitter and a single SPP. Such hybrid
systems connect two fundamentally different quantum worlds of electromagnetic
fields and emitters and open up new opportunities for exploring intriguing lightmatter interactions like Purcell effect, vacuum Rabi splitting and the optical Stark
effect on nanoscale. Recently, coupling strengths of as high as 350 meV have been
observed in metal-semiconductor hybrid nanostructures [8, 14, 24]. Therefore, it is
possible to observe light-matter interaction in these hybrid nanostructures even at
room temperature without any need for a closed cavity. One of the central goals for
hybrid systems is to control light via light by efficiently generating non-classical
entangled states of light and matter. Fundamentally new types of all-optical devices,
e.g. quantum gates and single-photon transistors have been already envisaged based
on coherent nonlinearity in these hybrid structures. Another related unexplored field
is the ability of strong coupling to modify the electromagnetic environment of an
emitter to modify potential energy landscapes and to control chemical reactions.
SPPs can also extend energy transfer range between two emitters, which otherwise
is only a few nm, To-date there appears to be no reports of how this resonant energy
transfer is modified in presence of coherent effects like strong coupling [8, 9, 14].
Here, we discuss the linear and nonlinear optical response of a metalsemiconductor hybrid nanostructures comprising a layer of J-aggregated dye
molecules in close proximity of a nano-slit array in a gold film schematically shown in
Fig. 5.1a. The hybrid nanostructures consist of a ∼ 50 nm thick J-aggregated cyanine
dye (2,2’dimethyl-8-phenyl-5,6,5’,6’-dibenzothiacarbocyanine chloride, Hayashibara Biochemicals Laboratories, Inc.) layer spin-coated onto a periodic nano-groove
array with 380–460 nm period in a gold film [8, 9, 14, 19, 20, 23, 25–27]. This system exhibits strong exciton-SPP coupling at room temperature hence is a potential
candidate to explore coherent nonlinear response in such hybrid structures. We start
by reviewing the linear optical response followed by few examples of experiments to
investigate coherent nonlinearity. Since the system under consideration consists of an
ensemble of molecules interacting with multiple SPP bands, the system behaves as
a collection of classical oscillators. Hence the photon number (intensity) dependent
Rabi frequency discussed earlier is not expected [8, 9, 14]. Nevertheless, as we shall
see in the following sections, the system offers unique possibility to control the Rabi
frequency as a function of pump intensity. Similar studies on how quantum emitters
and SPPs interact in hybrid structures may lead to advances in several directions and
will certainly unravel intriguing phenomena.