36 research outputs found
Deducing effective light transport parameters in optically thin systems
We present an extensive Monte Carlo study on light transport in optically
thin slabs, addressing both axial and transverse propagation. We completely
characterize the so-called ballistic-to-diffusive transition, notably in terms
of the spatial variance of the transmitted/reflected profile. We test the
validity of the prediction cast by diffusion theory, that the spatial variance
should grow independently of absorption and, to a first approximation, of the
sample thickness and refractive index contrast. Based on a large set of
simulated data, we build a freely available look-up table routine allowing
reliable and precise determination of the microscopic transport parameters
starting from robust observables which are independent of absolute intensity
measurements. We also present the Monte Carlo software package that was
developed for the purpose of this study
Diffusion of light in semitransparent media
Light diffusion is usually associated with thick, opaque media. Indeed,
multiple scattering is necessary for the onset of the diffusive regime and such
condition is generally not met in almost transparent media. Nonetheless, at
long enough times, transport in an infinite thin slab is still determined by a
multiple scattering process whose complete characterization is lacking. In this
paper we show that, after a short transient, the mean square width of the
transmitted intensity still exhibits a simple linear increase with time as
predicted by diffusion theory, even at optical thickness as low as one.
Interestingly, such linear growth is predicted not to depend neither on the
slab thickness nor on its refractive index contrast, yet the accuracy of this
simple approximation in the ballistic-to-diffusive regime hasn't been
investigated so far. By means of Monte Carlo simulations, we find clear
evidence that boundary conditions play an active role in redefining the very
asymptotic value of the diffusion coefficient by directly modifying the
statistical distributions underlying light transport in such media. In this
respect, we demonstrate the need to distinguish between a set of intrinsic and
effective transport parameters, whose relation and interplay with boundary
conditions remains to be fully understood
A Molecule‐Based Single‐Photon Source Applied in Quantum Radiometry
Single photon sources (SPSs) based on quantum emitters hold promise in
quantum radiometry as metrology standard for photon fluxes at the low light
level. Ideally this requires control over the photon flux in a wide dynamic
range, sub-Poissonian photon statistics and narrow-band emission spectrum. In
this work, a monochromatic single-photon source based on an organic dye
molecule is presented, whose photon flux is traceably measured to be adjustable
between 144 000 and 1320 000 photons per second at a wavelength of (785.6 +/-
0.1) nm, corresponding to an optical radiant flux between 36.5 fW and 334 fW.
The high purity of the single-photon stream is verified, with a second-order
autocorrelation function at zero time delay below 0.1 throughout the whole
range. Featuring an appropriate combination of emission properties, the
molecular SPS shows here application in the calibration of a silicon
Single-Photon Avalanche Detector (SPAD) against a low-noise analog silicon
photodiode traceable to the primary standard for optical radiant flux (i.e. the
cryogenic radiometer). Due to the narrow bandwidth of the source, corrections
to the SPAD detection efficiency arising from the spectral power distribution
are negligible. With this major advantage, the developed device may finally
realize a low-photon-flux standard source for quantum radiometry
Cold and Hot Spots: from Inhibition to Enhancement by Nanoscale Phase Tuning of Optical Nanoantennas
Optical nanoantennas are well-known for the
confinement of light into nanoscale hot spots, suitable for emission
enhancement and sensing applications. Here, we show how control
of the antenna dimensions allows tuning the local optical phase,
hence turning a hot spot into a cold spot. We manipulate the local
intensity exploiting the interference between driving and scattered
field. Using single molecules as local detectors, we experimentally
show the creation of subwavelength pockets with full suppression
of the driving field. Remarkably, together with the cold excitation
spots, we observe inhibition of emission by the phase-tuned nanoantenna. The fluorescence lifetime of a molecule scanned in such
volumes becomes longer, showing slow down of spontaneous decay. In conclusion, the spatial phase of a nanoantenna is a powerful
knob to tune between enhancement and inhibition in a 3-dimensional subwavelength volume.Peer ReviewedPostprint (author's final draft
Singular Spectrum Analysis of Two Photon Interference from Distinct Quantum Emitters
Two-photon interference underlies the functioning of many quantum photonics
devices. It also serves as the prominent tool for testing the
indistinguishability of distinct photons. However, as their time-spectral
profile becomes more involved, extracting relevant parameters, foremost the
central frequency difference, may start suffering difficulties. In a parametric
approach, these arise from the need for an exhaustive model combined with
limited count statistics. Here we discuss a solution to curtail these effects
on the evaluation of frequency separation relying on a semiparametric method.
The time trace of the quantum interference pattern of two photons from two
independent solid-state emitters is preprocessed by means of singular spectral
analysis before inspecting its spectral content. This approach allows to single
out the relevant oscillations from both the envelope and the noise, without
resorting to fitting. This opens the way for robust and efficient on-line
monitoring of quantum emitters
A 3D Polymeric Platform for Photonic Quantum Technologies
open10The successful development of future photonic quantum technologies will much depend on the possibility of realizing robust and scalable nanophotonic devices. These should include quantum emitters like on-demand single-photon sources and non-linear elements, provided their transition linewidth is broadened only by spontaneous emission. However, conventional strategies to on-chip integration, based on lithographic processes in semiconductors, are typically detrimental to the coherence properties of the emitter. Moreover, such approaches are difficult to scale and bear limitations in terms of geometries. Here an alternative platform is discussed, based on molecules that preserve near-Fourier-limited fluorescence even when embedded in polymeric photonic structures. 3D patterns are achieved via direct laser writing around selected molecular emitters, with a fast, inexpensive, and scalable fabrication process. By using an integrated polymeric design, detected photon counts of about 2.4 Mcps from a single cold molecule are reported. The proposed technology will allow for competitive organic quantum devices, including integrated multi-photon interferometers, arrays of indistinguishable single-photon sources, and hybrid electro-optical nanophotonic chips.openColautti, Maja; Lombardi, Pietro; Trapuzzano, Marco; Piccioli, Francesco S.; Pazzagli, Sofia; Tiribilli, Bruno; Nocentini, Sara; Cataliotti, Francesco S.; Wiersma, Diederik S.; Toninelli, CostanzaColautti, Maja; Lombardi, Pietro; Trapuzzano, Marco; Piccioli, Francesco S.; Pazzagli, Sofia; Tiribilli, Bruno; Nocentini, Sara; Cataliotti, Francesco S.; Wiersma, Diederik S.; Toninelli, Costanz
Single photon sources for quantum radiometry: a brief review about the current state-of-the-art
Single-photon sources have a variety of applications. One of these is quantum radiometry, which is reported on in this paper in the form of an overview, specifically of the current state of the art in the application of deterministic single photon sources to the calibration of single photon detectors. To optimize single-photon sources for this purpose, extensive research is currently carried out at the European National Metrology Institutes (NMIs), in collaboration with partners from universities. Single-photon sources of different types are currently under investigation, including sources based on defect centres in (nano-)diamonds, on molecules and on semiconductor quantum dots. We will present, summarise, and compare the current results obtained at European NMIs for single-photon sources in terms of photon flux, single-photon purity, and spectral power distribution as well as the results of single-photon detector calibrations carried out with this type of light sources.DFG, 390837967, EXC 2123: QuantumFrontiers - Licht und Materie an der Quantengrenz