arXiv subjects

Valentina Krachmalnicoff

Publications and source records attributed to Valentina Krachmalnicoff.

At least 19 recordsLinked to original sources

arXiv2026

Near-field Dressing of Thermal Emission

Radiative heat transfer at subwavelength distances is generally understood as enhanced energy exchange mediated by photon tunnelling between neighboring bodies. While near-field interactions can dramatically increase mutual heat transfer, whether they also modify the thermal radiation emitted by the bodies themselves remains an open question. Here we experimentally show that near-field electromagnetic coupling reshapes far-field thermal emission through a distance-dependent dressed emissivity. Using a dual-probe calorimetric platform, we independently monitor the radiative balance of two borosilicate microspheres over separations ranging from 120 micrometers to a few hundred nanometers, spanning the transition from the far field to the near field. Nanowatt-resolved differential radiometry reveals asymmetric heat fluxes and a non-monotonic response of the hotter sphere, demonstrating that thermal radiation is governed not only by emitter-bath interactions but also by coupling to the surrounding photonic environment. By analyzing the total power exchanged between the coupled system and the external thermal bath, we directly extract a dressed emissivity and show that near-field interactions renormalize the far-field thermal emission of the pair through a redistribution of the electromagnetic modes available to thermal fluctuations. These observations provide direct experimental evidence that thermal emitters are dressed by their electromagnetic environment, establishing a thermal analogue of the Purcell effect.

physics.optics↗

arXiv2026

Photon thermalization in an open and disordered scattering medium

Thermalization of light, where photons acquire a temperature and chemical potential analogous to a material gas, remains a striking yet experimentally elusive manifestation of quantum statistical physics. To date, it has been realized only in carefully engineered photonic environments that enforce repeated absorption-emission cycles. Here we show that such thermalization can emerge in a radically simpler setting: an open scattering medium. Using a pumped fluorescent dye solution doped with colloidal particles, we demonstrate that multiple scattering alone suffices to trap photons long enough to drive them to thermal equilibrium. The emitted radiation follows a Bose-Einstein distribution with a finite chemical potential, independently tunable via optical pumping, while its temperature is set by the host medium. A clear spectroscopic signature of thermalization is observed as a plateau at the sample temperature over a finite spectral range. Our results establish disordered scattering media as a generic platform for photon thermalization, extending this fundamental phenomenon beyond resonant cavities and opening new routes towards cavity-free photonic thermodynamics and thermal light sources operating under ambient conditions.

physics.optics↗

arXiv2026

Second-harmonic generation holography with polarization multiplexing for label-free collagen characterization and imaging

Digital holography is an interference-based imaging technique capable of recording both the amplitude and phase of an electromagnetic field. It can be obtained at the laser illumination wavelength, but also with second-harmonic generation, since the latter is produced in a coherent process. Here we describe the development of a harmonic holographic microscope for 3D single-shot mapping of second-harmonic emitters. The knowledge of the scattered field, in amplitude and phase, in a given plane, that of the camera, allows its reconstruction in any other plane using the angular spectrum representation of the optical fields, a process called 3D numerical back-propagation. In order to probe the polarization dependence of the sample nonlinear response, we implement polarization multiplexing, in which a Wollaston prism creates two off-axis reference beams with orthogonal polarizations and non-parallel propagation directions. Each reference only interferes with the corresponding polarization component in the sample SHG emission, thus providing two independent sets of interference fringes which are easily separated in the angular spectrum representation. From a single measurement, two second-harmonic fields corresponding to orthogonal polarizations can be back-propagated. In the particular case of collagen, the second-harmonic polarization state can reveal the orientation or disorder of molecules and fibers. We demonstrate the feasibility of the method by reconstructing the spatial distribution of the second-harmonic field generated by collagen fibers in a rat-tail tendon sample and show that polarization-multiplexed holography can provide single-shot 3D mapping of biophysical parameters such as the helical pitch angle of collagen molecules.

physics.optics↗

arXiv2025

Nano-resolved sensing of 3D electromagnetic fields via single emitters' extreme variation of enhanced spontaneous emission

Controlling quantum light-matter interactions at scales smaller than the diffraction limit at the single quantum emitter level is a critical challenge to the goal of advancing quantum technologies. We introduce a novel material platform that enables precise engineering of spontaneous emission changes in molecular single emitters through 3D nanofields. This platform is based on a 3D hollow plasmonic nanomaterial arranged in a square lattice, uniformly scalable to the centimeter scale while maintaining unit cell geometry. This coupled system leads to billions of Purcell-enhanced single emitters integrated into a nanodevice. Using far-field single-molecule super-resolution microscopy, we investigate emission modifications at the single-emitter level, enabling molecular position sensing with resolution surpassing the diffraction limit. By combining the nanolocalization with time correlation single photon counting, we probe molecule per molecule enhanced quantum light-matter interactions. This 3D plasmonic geometry significantly enhances light-matter interactions, revealing a broad range of lifetimes -- from nanoseconds to picoseconds -- significantly increasing the local density of states in a manner that depends on both molecular position and dipole orientation, offering extreme position sensitivity within the 3D electromagnetic landscape. By leveraging these plasmonic nanostructures and our method for measuring single-molecule Purcell-enhanced nano-resolved maps, we enable fine-tuned control of light-matter interactions. This approach enables the on-demand control of fast single-photon sources at room temperature, providing a powerful tool for molecular sensing and quantum applications at the single-emitter level.

physics.optics↗

arXiv2025

Non-monotonic radiative heat transfer in the transition from far field to near field

We present high precision measurements of the radiative heat transfer of a glass microsphere immersed in a thermal bath in vacuum facing three different planar substrates (SiO2, SiC and Au), which exhibit very different optical behaviors in the infrared region. Using a thermoresistive probe on a cantilever, we show the nonmonotonic behavior of the radiative flux between the microsphere and its environment when the microsphere is brought closer to the substrate in the far-field to near-field transition regime. We demonstrate that this unexpected behavior is related to the singularities of dressed emission mechanisms in this three-body system sphere-substrate-bath with respect to the separation distance.

cond-mat.mes-hall↗

arXiv2021

Hybrid modes in a single thermally excited asymmetric dimer antenna

The study of hybrid modes in a single dimer of neighboring antennas is an essential step to optimize the far-field electromagnetic (EM) response of large-scale metasurfaces or any complex antenna structure made up of subwavelength building blocks. Here we present far-field infrared spatial modulation spectroscopy (IR-SMS) measurements of a single thermally excited asymmetric dimer of square metal-insulator-metal (MIM) antennas separated by a nanometric gap. Through thermal fluctuations, all the EM modes of the antennas are excited and hybrid bonding and antibonding modes can be observed simultaneously. We study the latter within a plasmon hybridization model, and analyse their effect on the far-field response.

physics.optics↗

arXiv2020

Quantitative measurement of the thermal contact resistance between a glass microsphere and a plate

Accurate measurements of the thermal resistance between micro-objects made of insulating materials are complex because of their small size, low conductivity, and the presence of various ill-defined gaps. We address this issue using a modified scanning thermal microscope operating in vacuum and in air. The sphere-plate geometry is considered. Under controlled heating power, we measure the temperature on top of a glass microsphere glued to the probe as it approaches a glass plate at room temperature with nanometer accuracy. In vacuum, a jump is observed at contact. From this jump in temperature and the modeling of the thermal resistance of a sphere, the sphere-plate contact resistance $ R_K=(1.4 \pm 0.18)\times10^7 \ \mathrm{K.W^{-1}}$ and effective radius $r=(36 \pm 4)$ nm are obtained. In air, the temperature on top of the sphere shows a decrease starting from a sphere-plate distance of 200 $\mathrm{μm}$. A jump is also observed at contact, with a reduced amplitude. The sphere-plate coupling out of contact can be described by the resistance shape factor of a sphere in front of a plate in air, placed in a circuit involving a series and a parallel resistance that are determined by fitting the approach curve. The contact resistance in air $R^*_K=(1.2 \pm 0.46)\times 10^7 \ \mathrm{K.W^{-1}}$ is then estimated from the temperature jump. The method is quantitative without requiring any tedious multiple-scale numerical simulation, and is versatile to describe the coupling between micro-objects from large distances to contact in various environments.

cond-mat.mtrl-sci↗

arXiv2019

Thermal emission from a single glass fiber

In this article, we study the thermal light emission from individual fibers of an industrial glass material, which are elementary building blocks of glass wool boards used for thermal insulation. Thermal emission spectra of single fibers of various diameters partially suspended on air are measured in the far-field by means of infrared spatial modulation spectroscopy.These experimental spectra are compared with the theoretical absorption efficiency spectra of cylindrical shaped fibers calculated analytically in the framework of Mie theory taking as an input the measured permittivity of the industrial glass material. An excellent qualitative agreement is found between the measured thermal radiation spectra and the theoretical absorption efficiency spectra.

physics.app-ph↗

arXiv2019

Cramér-Rao analysis of lifetime estimations in time-resolved fluorescence microscopy

Measuring the lifetime of fluorescent emitters by time-correlated single photon counting (TCSPC) is a routine procedure in many research areas spanning from nanophotonics to biology. The precision of such measurement depends on the number of detected photons but also on the various sources of noise arising from the measurement process. Using Fisher information theory, we calculate the lower bound on the precision of lifetime estimations for mono-exponential and bi-exponential distributions. We analyse the dependence of the lifetime estimation precision on experimentally relevant parameters, including the contribution of a non-uniform background noise and the instrument response funtion (IRF) of the setup. We also provide an open-source code to determine the lower bound on the estimation precision for any experimental conditions. Two practical examples illustrate how this tool can be used to reach optimal precision in time-resolved fluorescence microscopy.

physics.ins-det↗

arXiv2019

Probing near-field light-matter interactions with single-molecule lifetime imaging

Nanophotonics offers a promising range of applications spanning from the development of efficient solar cells to quantum communications and biosensing. However, the ability to efficiently couple fluorescent emitters with nanostructured materials requires to probe light-matter interactions at subwavelength resolution, which remains experimentally challenging. Here, we introduce an approach to perform super-resolved fluorescence lifetime measurements on samples that are densely labelled with photo-activatable fluorescent molecules. The simultaneous measurement of the position and the decay rate of the molecules provides a direct access to the local density of states (LDOS) at the nanoscale. We experimentally demonstrate the performance of the technique by studying the LDOS variations induced in the near field of a silver nanowire, and we show via a Cramér-Rao analysis that the proposed experimental setup enables a single-molecule localisation precision of 6 nm.

physics.optics↗

arXiv2018

Imaging light scattered by a subwavelength nanofiber, from near field to far field

We present a direct experimental investigation of the optical field distribution around a suspended tapered optical nanofiber by means of a fluorescent scanning probe. Using a 100 nm diameter fluorescent bead as a probe of the field intensity, we study interferences made by a nanofiber (400 nm diameter) scattering a plane wave (568 nm wavelength). Our scanning fluorescence near-field microscope maps the optical field over 36 $μ$m$^2$, with $λ/ 5$ resolution, from contact with the surface of the nanofiber to a few micrometers away. Comparison between experiments and Mie scattering theory allows us to precisely determine the emitter-nanofiber distance and experimental drifts.

physics.optics↗

arXiv2017

Polarisation control of linear dipole radiation using spin-momentum locking of light

We experimentally demonstrate that a linear dipole is not restricted to emit linearly polarised light, provided it is embedded in the appropriate nanophotonic environment. We observe emission of various elliptical polarisations by a linear dipole including circularly polarised light, without the need for birefringent components. We further show that the emitted state of polarisation can theoretically span the entire Poincare sphere. The experimental demonstration is based on elongated gold nanoparticles (nanorods) deposited on an optical nanofibre and excited by a free-space laser beam. The light directly collected in the guided mode of the nanofibre is analysed in regard to the azimuthal position and orientation of the nanorods, observed by means of scanning electron microscopy. This work constitutes a demonstration of the mapping between purely geometrical degrees of freedom of a light source and all polarisation states and could open the way to new methods for polarisation control of light sources at the nanoscale.

quant-ph↗

arXiv2016

Enhancement and Inhibition of Spontaneous Photon Emission by Resonant Silicon Nanoantennas

Substituting noble metals for high-index dielectrics has recently been proposed as an alternative strategy in nanophotonics to design broadband optical resonators and circumvent the ohmic losses of plasmonic materials. In this report, we demonstrate that subwavelength silicon nanoantennas can manipulate the photon emission dynamics of fluorescent molecules. In practice, it is showed that dielectric nanoantennas can both increase and decrease the local density of optical states (LDOS) at room temperature, a process that is inaccessible with noble metals at the nanoscale. Using scanning probe microscopy, we analyze quantitatively, in three dimensions, the near-field interaction between a 100 nm fluorescent nanosphere and silicon nanoantennas with diameters ranging between 170 nm and 250 nm. Associated to numerical simulations, these measurements indicate increased or decreased total spontaneous decay rates by up to 15 % and a gain in the collection efficiency of emitted photons by up to 85 %. Our study demonstrates the potential of silicon-based nanoantennas for the low-loss manipulation of solid-state emitters at the nanoscale and at room temperature.

physics.optics↗

arXiv2016

Correlated spontaneous emission of fluorescent emitters mediated by single plasmons

Manipulating the spontaneous emission of a fluorescent emitter can be achieved by placing the emitter in a nanostructured environment. A privileged spot is occupied by plasmonic structures that provide a strong confinement of the electromagnetic field, which results in an enhancement of the emitter-environment interaction. While plasmonic nanostructures have been widely exploited to control the emission properties of single photon emitters, performing the coupling between quantum emitters with plasmons poses a huge challenge. In this Letter we report on a first crucial step towards this goal by the observation of correlated emission between a single CdSe/CdS/ZnS quantum dot exhibiting single photon statistics and a fluorescent nanobead located micrometers apart. This is accomplished by coupling both emitters to a silver nanowire. Single-plasmons are created on the latter from the quantum dot, and transfer energy to excite in turn the fluorescent nanobead.

physics.optics↗

arXiv2016

Near-field to far-field characterization of speckle patterns generated by disordered nanomaterials

We study the intensity spatial correlation function of optical speckle patterns above a disordered dielectric medium in the multiple scattering regime. The intensity distributions are recorded by scanning near-field optical microscopy (SNOM) with sub-wavelength spatial resolution at variable distances from the surface in a range which spans continuously from the near-field (distance $ \ll λ$) to the far-field regime (distance $\gg λ$). The non-universal behavior at sub-wavelength distances reveals the connection between the near-field speckle pattern and the internal structure of the medium.

physics.optics↗

arXiv2014

Anisotropy in s-wave Bose-Einstein condensate collisions and its relationship to superradiance

We report the experimental realization of a single-species atomic four-wave mixing process with BEC collisions for which the angular distribution of scattered atom pairs is not isotropic, despite the collisions being in the $s$-wave regime. Theoretical analysis indicates that this anomalous behavior can be explained by the anisotropic nature of the gain in the medium. There are two competing anisotropic processes: classical trajectory deflections due to the mean-field potential, and Bose enhanced scattering which bears similarity to super-radiance. We analyse the relative importance of these processes in the dynamical buildup of the anisotropic density distribution of scattered atoms, and compare to optically pumped super-radiance.

cond-mat.quant-gas↗

arXiv2013

Towards a full characterization of a plasmonic nanostructure with a fluorescent near-field probe

We report on the experimental and theoretical study of the spatial fluctuations of the local density of states (EM-LDOS) and of the fluorescence intensity in the near-field of a gold nanoantenna. EM-LDOS, fluorescence intensity and topography maps are acquired simultaneously by scanning a fluorescent nanosource grafted on the tip of an atomic force microscope at the surface of the sample. The results are in good quantitative agreement with numerical simulations. This work paves the way for a full near-field characterization of an optical nanoantenna.

physics.optics↗

arXiv2010

Sub-Poissonian number differences in four-wave mixing of matter waves

We demonstrate sub-Poissonian number differences in four-wave mixing of Bose-Einstein condensates of metastable helium. The collision between two Bose-Einstein condensates produces a scattering halo populated by pairs of atoms of opposing velocities, which we divide into several symmetric zones. We show that the atom number difference for opposing zones has sub-Poissonian noise fluctuations whereas that of nonopposing zones is well described by shot noise. The atom pairs produced in a dual number state are well adapted to sub shot-noise interferometry and studies of Einstein-Podolsky-Rosen-type nonlocality tests.

cond-mat.quant-gas↗