arXiv subjects

Dan Oron

Publications and source records attributed to Dan Oron.

At least 19 recordsLinked to original sources

arXiv2026

Continuous-Wave SOFISM with SPAD Array Detection

We present a continuous-wave (CW) implementation of super-resolution optical fluctuation imaging with image scanning microscopy (SOFISM) using a pixelated single-photon avalanche diode (SPAD) detector camera. In a scanning-based geometry, SOFISM requires fluorescence fluctuations on timescales compatible with the pixel dwell time while maintaining sufficient signal under confocal excitation. Photoswitchable fluorophores in an aqueous switching buffer containing the glucose oxidase-catalase oxygen-scavenging system (GLOXY) and mercaptoethylamine (MEA) were therefore used to promote blinking and reduce photobleaching. Correlation analysis of sparse-emitter measurements showed that Alexa Fluor 647 (AF647) exhibits microsecond-scale fluctuation dynamics suitable for CW SOFISM and guided the choice of imaging conditions for scanned samples. Frame rate and delay accumulation were optimized from detector-pair subset variability using a mean-to-STD criterion. The optimal binning time was 2.5 $\mu$s, underscoring the advantage of SPAD-based detection for resolving the relevant fluctuation dynamics. The method was demonstrated on HeLa cell microtubules labeled with AF647, yielding improved spatial resolution in the constructed SOFISM images compared with the corresponding ISM images. Additional super-resolved images from samples labeled with CF568 and Alexa Fluor 555 (AF555) showed the approach is readily generalizable to other fluorophores. These results establish CW SOFISM as a practical fluctuation-based super-resolution method for confocal microscopy.

physics.optics↗

arXiv2025

Correlations in the Binding Energy of Triexcitons and Biexcitons in Single CdSe/CdS Nanoplatelets Revealed by Heralded Spectroscopy

Semiconductor nanoplatelets present reduced Auger recombination, giving rise to enhanced multiexciton emission. This virtue makes them good candidates to investigate higher-order carrier dynamics, allowing to extract important excitonic properties, such as biexciton and triexciton binding energies that highly influence applications involving high excitation fluxes. Here, we explore triexciton emission, emanating from single core/shell CdSe/CdS nanoplatelets. We apply heralded post-selection of photon triplets using an advanced home-built single-photon spectrometer in order to resolve the triexciton$-$biexciton$-$exciton$-$ground state cascaded relaxation both in time and spectrum, and unambiguously determine the triexciton relaxation route and interaction nature. The results show a characteristic blue shift of the biexciton and triexciton, pointing to repulsive multiexciton interaction in the nanoplatelets under study. The relatively small measured energy shift of the triexciton (5.9 $\pm$ 0.7 meV) indicates that it recombines through the 1S bands rather than the 1P bands, in agreement with findings on other colloidal quantum dot systems. Most importantly, the strong correlation between the biexciton and triexciton binding energies, and the ability to tune them via control of the particle dimensions and composition, paves the way for developing emitters of nearly degenerate photon triplets.

cond-mat.mes-hall↗

arXiv2025

Unraveling Size Dependent Bi- and Tri-exciton Characteristics in CdSe/CdS Core/Shell Quantum Dots via Ensemble Time Gated Heralded Spectroscopy

Multiexcitons (MXs) in quantum dots (QDs) manifest many body interactions under quantum confinement. Beyond this fundamental interest, MXs are of importance in numerous optoelectronic applications including QD lasing, light emitting diodes and photocatalysis. Yet, the strong interactions between MXs leading to rapid non-radiative decay introduce challenges for their characterization. While so far, the measurement techniques rely either on indirect methods or on single particle studies, herein we introduce a new method to study MXs in QD ensembles utilizing spectrally resolved time-gated heralded spectroscopy. With this approach we extract the biexciton binding energies in a series of CdSe/CdS QD ensembles of several core/shell sizes, manifesting a transition between attractive and repulsive exciton-exciton interactions. Additionally, for triexcitons, which involve occupation of two excitons in the 1s energy levels, as well as one exciton in the 1p energy levels, we address the open issues of isolating the spectra of the two triexciton pathways from one another and from high-order MXs, and extract the MX lifetimes. The measurements on ensembles provide high photon counts and low noise levels, and alongside the time-gated heralded approach thus enable the observation of MX characteristics that are difficult to resolve in single particle studies. The approach can be further implemented in the characterization of the energies and lifetimes of MXs in other QD systems to enable rapid characterization and understanding of the MX properties. Such insight bears relevance to optoelectronic applications ranging from lasing to electroluminescent devices to quantum light sources.

cond-mat.mes-hall↗

arXiv2025

Broadband Emission via a Photon Avalanche in a Lanthanide-Trimesic Acid Metal-Organic Framework

Infrared-triggered photon upconversion in porous materials presents intriguing prospects for combined functionalities such as molecular sponge, energy harvesting and conversion functionalities. Metal-organic frameworks (MOFs) are one of the most versatile classes of porous crystals. So far only two-photon upconverting processes have been realized in MOFs both by ligand based triplet-triplet annihilation and directly in lanthanide ions. Here we report on Yb3+/Er3+-trimesate-based MOFs that exhibit photon avalanche (PA) characteristics. The PA process conventionally occurs through cross-relaxation within the lanthanide emitter manifold. In contrast, here PA proceeds in the organic molecule part and relies on a cooperative process, involving multiple emission centers. The IR photons are first absorbed and upconverted into high energy electronic population by the action of the lanthanide ions (Yb3+ and Er3+ are the sensitizer and the activator, respectively). Subsequently, the electrons are funneled into electronically coupled triplet states of the trimesate ligand, enabling accumulation in the organic matrix. This reservoir acts as source for a highly nonlinear spectrally broadband emission, arising mainly from ligand triplet states. The nonlinearity factor is comparable with the well-established PA inorganic nanoparticles. We prove that the PA is strongly related to the degree of crystallinity of the MOF: not well-formed frameworks support only the characteristic Er3+ emission with only linear increase as a function of the excitation power. Our work paves a path towards vastly expanding the range of materials exhibiting PA, well beyond a limited set of lanthanide ions. Moreover, it provides a path for much broader control of the PA emission characteristics.

physics.optics↗

arXiv2024

Massively Multiplexed Wide-field Photon Correlation Sensing

Temporal photon correlations have been a crucial resource for quantum and quantum-enabled optical science for over half a century. However, attaining non-classical information through these correlations has typically been limited to a single point (or at best, a few points) at-a-time. We perform here a massively multiplexed wide-field photon correlation measurement using a large $500\times500$ single-photon avalanche diode array, the SwissSPAD3. We demonstrate the performance of this apparatus by acquiring wide-field photon correlation measurements of single-photon emitters, and illustrate two applications of the attained quantum information: wide-field emitter counting and quantum-enabled super-resolution imaging (by a factor of $\sqrt{2})$. The considerations and limitations of applying this technique in a practical context are discussed. Ultimately, the realization of massively multiplexed wide-field photon correlation measurements can accelerate quantum sensing protocols and quantum-enabled imaging techniques by orders of magnitude.

physics.optics↗

arXiv2024

Advances in quantum imaging

Modern imaging technologies are widely based on classical principles of light or electromagnetic wave propagation. They can be remarkably sophisticated, with recent successes ranging from single molecule microscopy to imaging far-distant galaxies. However, new imaging technologies based on quantum principles are gradually emerging. They can either surpass classical approaches or provide novel imaging capabilities that would not otherwise be possible. {Here }we provide an overview {of the most recently developed quantum imaging systems, highlighting the non-classical properties of sources such as bright squeezed light, entangled photons, and single-photon emitters that enable their functionality.} We outline potential upcoming trends and the associated challenges, all driven by a central inquiry, which is to understand whether quantum light can make visible the invisible.

quant-ph↗

arXiv2024

Phonon-driven wavefunction localization promotes room-temperature, pure single-photon emission in large organic-inorganic lead-halide quantum dots

In lead halide perovskites (APbX3), the effect of the A-site cation on optical and electronic properties has initially been thought to be marginal. Yet, evidence of beneficial effects on solar cell performance and light emission is accumulating. Here, we report that the A-cation in soft APbBr3 colloidal quantum dots (QDs) controls the phonon-induced localization of the exciton wavefunction. Insights from ab initio molecular dynamics and single-particle fluorescence spectroscopy demonstrate that anharmonic lattice vibrations and the resulting polymorphism act as an additional confinement potential. Avoiding the trade-off between single-photon purity and optical stability faced by downsizing conventional QDs into the strong confinement regime, dynamical phonon-induced confinement in large organic-inorganic perovskite QDs enables bright (10^6 photons/s), stable (> 1h), and pure (> 95%) single-photon emission in a widely tuneable spectral range (495-745 nm). Strong electron-phonon interaction in soft perovskite QDs provides an unconventional route toward the development of scalable room-temperature quantum light sources.

cond-mat.mtrl-sci↗

arXiv2024

Super-resolved CARS by coherent image scanning

We present super-resolved coherent anti-Stokes Raman scattering (CARS) microscopy by implementing phase-resolved image scanning microscopy (ISM), achieving up to two-fold resolution increase as compared with a conventional CARS microscope. Phase-sensitivity is required for the standard pixel-reassignment procedure since the scattered field is coherent, thus the point-spread function (PSF) is well-defined only for the field amplitude. We resolve the complex field by a simple add-on to the CARS setup enabling inline interferometry. Phase-sensitivity offers additional contrast which informs the spatial distribution of both resonant and nonresonant scatterers. As compared with alternative super-resolution schemes in coherent nonlinear microscopy, the proposed method is simple, requires only low-intensity excitation, and is compatible with any conventional forward-detected CARS imaging setup.

physics.optics↗

arXiv2023

Quantum light microscopy

Much of our progress in understanding microscale biology has been powered by advances in microscopy. For instance, super-resolution microscopes allow the observation of biological structures at near-atomic-scale resolution, while multi-photon microscopes allow imaging deep into tissue. However, biological structures and dynamics still often remain out of reach of existing microscopes, with further advances in signal-to-noise, resolution and speed needed to access them. In many cases, the performance of microscopes is now limited by quantum effects -- such as noise due to the quantisation of light into photons or, for multi-photon microscopes, the low cross-section of multi-photon scattering. These limitations can be overcome by exploiting features of quantum mechanics such as entanglement. Quantum effects can also provide new ways to enhance the performance of microscopes, such as new super-resolution techniques and new techniques to image at difficult to reach wavelengths. This review provides an overview of these various ways in which quantum techniques can improve microscopy, including recent experimental progress. It seeks to provide a realistic picture of what is possible, and what the constraints and opportunities are.

quant-ph↗

arXiv2023

Two Biexciton Types Coexisting in Coupled Quantum Dot Molecules

Coupled colloidal quantum dot molecules are an emerging class of nanomaterials, introducing new degrees of freedom for designing quantum dot-based technologies. The properties of multiply excited states in these materials are crucial to their performance as quantum light emitters but cannot be fully resolved by existing spectroscopic techniques. Here we study the characteristics of biexcitonic species, which represent a rich landscape of different configurations, such as segregated and localized biexciton states. To this end, we introduce an extension of Heralded Spectroscopy to resolve different biexciton species in the prototypical CdSe/CdS coupled quantum dot dimer system. We uncover the coexistence and interplay of two distinct biexciton species: A fast-decaying, strongly-interacting biexciton species, analogous to biexcitons in single quantum dots, and a long-lived, weakly-interacting species corresponding to two nearly-independent excitons separated to the two sides of the coupled quantum dot pair. The two biexciton types are consistent with numerical simulations, assigning the strongly-interacting species to two excitons localized at one side of the quantum dot molecule and the weakly-interacting species to excitons segregated to the two quantum dot molecule sides. This deeper understanding of multiply excited states in coupled quantum dot molecules can support the rational design of tunable single- or multiple-photon quantum emitters.

cond-mat.mes-hall↗

arXiv2023

Resolving the emission transition dipole moments of single doubly-excited seeded nanorods via heralded defocused imaging

Semiconductor nanocrystal emission polarization is a crucial probe of nanocrystal physics and an essential factor for nanocrystal-based technologies. While the transition dipole moment of the lowest excited state to ground state transition is well characterized, the dipole moment of higher multiexcitonic transitions is inaccessible via most spectroscopy techniques. Here, we realize direct characterization of the doubly-excited state relaxation transition dipole by heralded defocused imaging. Defocused imaging maps the dipole emission pattern onto a fast single-photon avalanche diode detector array, allowing the post-selection of photon pairs emitted from the biexciton-exciton emission cascade and resolving the differences in transition dipole moments. Type-I1/2 seeded nanorods exhibit higher anisotropy of the biexciton-to-exciton transition compared to the exciton-to-ground state transition. In contrast, type-II seeded nanorods display a reduction of biexciton emission anisotropy. These findings are rationalized in terms of an interplay between transient dynamics of the refractive index and the excitonic fine structure.

cond-mat.mes-hall↗

arXiv2021

Super-resolved Second Harmonic Generation Imaging by Coherent Image Scanning Microscopy

We extend image scanning microscopy to second harmonic generation (SHG) by extracting the complex field amplitude of the second-harmonic beam. While the theory behind coherent image scanning microscopy (ISM) is known, an experimental demonstration wasn't yet established. The main reason is that the naive intensity-reassignment procedure cannot be used for coherent scattering as the point spread function is now defined for the field amplitude rather than for the intensity. We use an inline interferometer to demonstrate super-resolved phase-sensitive SHG microscopy by applying the ISM reassignment machinery on the resolved field. This scheme can be easily extended to third harmonic generation and stimulated Raman microscopy schemes.

physics.optics↗

arXiv2021

Heralded spectroscopy reveals exciton-exciton correlations in single colloidal quantum dots

Multiply-excited states in semiconductor quantum dots feature intriguing physics and play a crucial role in nanocrystal-based technologies. While photoluminescence provides a natural probe to investigate these states, room temperature single-particle spectroscopy of their emission has so far proved elusive due to the temporal and spectral overlap with emission from the singly-excited and charged states. Here we introduce biexciton heralded spectroscopy, enabled by a single-photon avalanche diode array based spectrometer. This allows us to directly observe biexciton-exciton emission cascades and measure the biexciton binding energy of single quantum dots at room temperature, even though it is well below the scale of thermal broadening and spectral diffusion. Furthermore, we uncover correlations hitherto masked in ensembles, of the biexciton binding energy with both charge-carrier confinement and fluctuations of the local electrostatic potential. Heralded spectroscopy has the potential of greatly extending our understanding of charge-carrier dynamics in multielectron systems and of parallelization of quantum optics protocols.

cond-mat.mes-hall↗

arXiv2021

Resolving the controversy in biexciton binding energy of cesium lead halide perovskite nanocrystals through heralded single-particle spectroscopy

Understanding exciton-exciton interaction in multiply-excited nanocrystals is crucial to their utilization as functional materials. Yet, for lead halide perovskite nanocrystals, which are promising candidates for nanocrystal-based technologies, numerous contradicting values have been reported for the strength and sign of their exciton-exciton interaction. In this work we unambiguously determine the biexciton binding energy in single cesium lead halide perovskite nanocrystals at room temperature. This is enabled by the recently introduced SPAD array spectrometer, capable of temporally isolating biexciton-exciton emission cascades while retaining spectral resolution. We demonstrate that CsPbBr$_3$ nanocrystals feature an attractive exciton-exciton interaction, with a mean biexciton binding energy of 10 meV. For CsPbI$_3$ nanocrystals we observe a mean biexciton binding energy that is close to zero, and individual nanocrystals show either weakly attractive or weakly repulsive exciton-exciton interaction. We further show that within ensembles of both materials, single-nanocrystal biexciton binding energies are correlated with the degree of charge-carrier confinement.

cond-mat.mes-hall↗

arXiv2020

Growth-Etch Metal-Organic Chemical Vapor Deposition Approach of WS2 Atomic-Layers

Metal organic chemical vapor deposition (MOCVD) is one of the main methodologies used for thin film fabrication in the semiconductor industry today and is considered one of the most promising routes to achieve large-scale and high-quality 2D transition metal dichalcogenides (TMDCs). However, if not taken special measures, MOCVD suffers from some serious drawbacks, such as small domain size and carbon contamination, resulting in poor optical and crystal quality, which may inhibit its implementation for the large-scale fabrication of atomic-thin semiconductors. Here we present a Growth-Etch MOCVD (GE-MOCVD) methodology, in which a small amount of water vapor is introduced during the growth, while the precursors are delivered in pulses. The evolution of the growth as a function of the amount of water vapor, the number and type of cycles and the gas composition is described. We show a significant domain size increase is achieved relative to our conventional process. The improved crystal quality of WS2 (and WSe2) domains was demonstrated by means of Raman spectroscopy, photoluminescence (PL) spectroscopy and HRTEM studies. Moreover, time-resolved PL studies show very long exciton lifetimes, comparable to those observed in mechanically exfoliated flakes. Thus, the GE-MOCVD approach presented here may facilitate their integration into a wide range of applications.

physics.app-ph↗

arXiv2020

Low Frequency Collinear Pre-Resonant Impulsive Stimulated Raman Spectroscopy

In this work we extend low frequency impulsive stimulated Raman microspectroscopy to the pre-electronic resonance regime. We use a broadband two color collinear pump probe scheme which can be readily extended to imaging. We discuss the difficulties unique to this type of measurements in the form of competing resonant two-photon processes and the means to overcome them. We successfully reduce the noise which arises due to those competing processes by eliminating the detected spectral components which do not contribute to the vibrational signature of the sample though introduce most of the noise. Finally, we demonstrate low-frequency spectroscopy of crystalline samples under near-resonant pumping showing both enhancement and spectral modification due to coupling with the electronic degree of freedom.

physics.optics↗

arXiv2020

SOFISM: Super-resolution optical fluctuation image scanning microscopy

Super-resolution optical microscopy is a rapidly evolving scientific field dedicated to imaging sub-wavelength sized objects, leaving its mark in multiple branches of biology and technology. While several super-resolution optical microscopy methods have become a common tool in life science imaging, new methods, supported by cutting-edge technology, continue to emerge. One rather recent addition to the super-resolution toolbox, image scanning microscopy (ISM), achieves an up to twofold lateral resolution enhancement in a robust and straightforward manner. To further enhance ISM's resolution in all three dimensions, we present and experimentally demonstrate here super-resolution optical fluctuation image scanning microscopy (SOFISM). Measuring the fluorescence fluctuation contrast in an ISM architecture, we obtain images with a x2.5 lateral resolution beyond the diffraction limit along with an enhanced axial resolution for a fixed cell sample labeled with commercially available quantum dots. The inherent temporal averaging of the ISM technique enables image acquisition of the fluctuation correlation contrast within millisecond scale pixel dwell times. SOFISM can therefore offer a robust path to achieve high resolution images within a slightly modified confocal microscope, using standard fluorescent labels and within reasonable acquisition times.

physics.optics↗

arXiv2019

Quantum correlation measurement with single photon avalanche diode arrays

Temporal photon correlation measurement, instrumental to probing the quantum properties of light, typically requires multiple single photon detectors. Progress in single photon avalanche diode (SPAD) array technology highlights their potential as high performance detector arrays for quantum imaging and photon number resolving (PNR) experiments. Here, we demonstrate this potential by incorporating a novel on-chip SPAD array with 55% peak photon detection probability, low dark count rate and crosstalk probability of 0.14% per detection, in a confocal microscope. This enables reliable measurements of second and third order photon correlations from a single quantum dot emitter. Our analysis overcomes the inter-detector optical crosstalk background even though it is over an order of magnitude larger than our faint signal. To showcase the vast application space of such an approach, we implement a recently introduced super-resolution imaging method, quantum image scanning microscopy (Q-ISM).

physics.optics↗