47 research outputs found
Quantum spectroscopy of plasmonic nanostructures
We use frequency entangled photons, generated via spontaneous parametric down
conversion, to measure the broadband spectral response of an array of gold
nanoparticles exhibiting Fano-type plasmon resonance. Refractive index sensing
of a liquid is performed by measuring the shift of the array resonance. This
method is robust in excessively noisy conditions compared with conventional
broadband transmission spectroscopy. Detection of a refractive index change is
demonstrated with a noise level 70 times higher than the signal, which is shown
to be inaccessible with the conventional transmission spectroscopy. Use of low
photon fluxes makes this method suitable for measurements of photosensitive
bio-samples and chemical substances.Comment: 11 pages, 5 figure
Measurement of infrared optical constants with visible photons
We demonstrate a new scheme of infrared spectroscopy with visible light
sources and detectors. The technique relies on the nonlinear interference of
correlated photons, produced via spontaneous parametric down conversion in a
nonlinear crystal. Visible and infrared photons are split into two paths and
the infrared photons interact with the sample under study. The photons are
reflected back to the crystal, resembling a conventional Michelson
interferometer. Interference of the visible photons is observed and it is
dependent on the phases of all three interacting photons: pump, visible and
infrared. The transmission coefficient and the refractive index of the sample
in the infrared range can be inferred from the interference pattern of visible
photons. The method does not require the use of potentially expensive and
inefficient infrared detectors and sources, it can be applied to a broad
variety of samples, and it does not require a priori knowledge of sample
properties in the visible range