171 research outputs found
Quantum theory of spontaneous and stimulated emission of surface plasmons
We introduce a quantization scheme that can be applied to surface waves
propagating along a plane interface. An important result is the derivation of
the energy of the surface wave for dispersive non-lossy media without invoking
any specific model for the dielectric constant. Working in Coulomb's gauge, we
use a modal representation of the fields. Each mode can be associated with a
quantum harmonic oscillator. We have applied the formalism to derive
quantum-mechanically the spontaneous emission rate of surface plasmon by a
two-level system. The result is in very good agreement with Green's tensor
approach in the non-lossy case. Green's approach allows also to account for
losses, so that the limitations of a quantum approach of surface plasmons are
clearly defined. Finally, the issue of stimulated versus spontaneous emission
has been addressed. Because of the increasing density of states near the
asymptote of the dispersion relation, it is quantitatively shown that the
stimulated emission probability is too small to obtain gain in this frequency
region.Comment: 14 pages, 5 figures, submitted to Phys. Rev. B
Balanced homodyne detection in second-harmonic generation microscopy
We demonstrate the association of two-photon nonlinear microscopy with
balanced homodyne detection for investigating second harmonic radiation
properties at nanoscale dimensions. Variation of the relative phase between
second-harmonic and fundamental beams is retrieved, as a function of the
absolute orientation of the nonlinear emitters. Sensitivity down to
approximately 3.2 photon/s in the spatio-temporal mode of the local oscillator
is obtained. This value is high enough to efficiently detect the coherent
second-harmonic emission from a single KTiOPO4 crystal of sub-wavelength size.Comment: 9 pages to appear in Applied Physics Letter
Two-photon real-time device for single-particle holographic tracking (red shot)
Three-dimension real-time tracking of single emitters is an emerging tool for
assessment of biological behavior as intraneuronal transport, for which
spatiotemporal resolution is crucial to understand the microscopic interactions
between molecular motors. We report the use of second harmonic signal from
nonlinear nanoparticles to localize them in a super-localization regime, down
to 15 nm precision, and at high refreshing rates, up to 1.1 kHz, allowing us to
track the particles in real-time. Holograms dynamically displayed on a digital
micro-mirror device are used to steer the excitation laser focus in 3D around
the particle on a specific pattern. The particle position is inferred from the
collected intensities using a maximum likelihood approach. The holograms are
also used to compensate for optical aberrations of the optical system. We
report tracking of particles moving faster than 30 m/s with an uncertainty
on the localization around 40 nm. We have been able to track freely moving
particles over tens of micrometers, and directional intracellular transport in
neurites
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