Origami nanogap electrodes for reversible nanoparticle trapping.

We present a facile desktop fabrication method for origami-based nanogap indium tin oxide (ITO) electrokinetic particle traps, providing a simplified approach compared to traditional lithographic techniques and effective trapping of nanoparticles. Our approach involves bending ITO thin films on optically transparent polyethylene terephthalate (PET), creating an array of parallel nanogaps. By strategically introducing weak points through cut-sharp edges, we successfully controlled the spread of nanocracks. A single crack spanning the constriction width and splitting the conductive layers forms a nanogap that can effectively trap small nanoparticles after applying an alternating electric potential across the nanogap. We analyze the conditions for reversible trapping and optimal performance of the nanogap ITO electrodes with optical microscopy and electrokinetic impedance spectroscopy. Our findings highlight the potential of this facile fabrication method for the use of ITO at active electro-actuated traps in microfluidic systems.

Noise-robust latent vector reconstruction in ptychography using deep generative models.

Computational imaging is increasingly vital for a broad spectrum of applications, ranging from biological to material sciences. This includes applications where the object is known and sufficiently sparse, allowing it to be described with a reduced number of parameters. When no explicit parameterization is available, a deep generative model can be trained to represent an object in a low-dimensional latent space. In this paper, we harness this dimensionality reduction capability of autoencoders to search for the object solution within the latent space rather than the object space. We demonstrate what we believe to be a novel approach to ptychographic image reconstruction by integrating a deep generative model obtained from a pre-trained autoencoder within an automatic differentiation ptychography (ADP) framework. This approach enables the retrieval of objects from highly ill-posed diffraction patterns, offering an effective method for noise-robust latent vector reconstruction in ptychography. Moreover, the mapping into a low-dimensional latent space allows us to visualize the optimization landscape, which provides insight into the convexity and convergence behavior of the inverse problem. With this work, we aim to facilitate new applications for sparse computational imaging such as when low radiation doses or rapid reconstructions are essential.

Maximum-likelihood estimation in ptychography in the presence of Poisson-Gaussian noise statistics: publisher's note.

This publisher's note contains a correction to Opt. Lett.48, 6027 (2023)10.1364/OL.502344.

Maximum-likelihood estimation in ptychography in the presence of Poisson-Gaussian noise statistics.

Optical measurements often exhibit mixed Poisson-Gaussian noise statistics, which hampers the image quality, particularly under low signal-to-noise ratio (SNR) conditions. Computational imaging falls short in such situations when solely Poissonian noise statistics are assumed. In response to this challenge, we define a loss function that explicitly incorporates this mixed noise nature. By using a maximum-likelihood estimation, we devise a practical method to account for a camera readout noise in gradient-based ptychography optimization. Our results, based on both experimental and numerical data, demonstrate that this approach outperforms the conventional one, enabling enhanced image reconstruction quality under challenging noise conditions through a straightforward methodological adjustment.

Precursor-free eruption triggered by edifice rupture at Nyiragongo volcano.

Classical mechanisms of volcanic eruptions mostly involve pressure buildup and magma ascent towards the surface1. Such processes produce geophysical and geochemical signals that may be detected and interpreted as eruption precursors1-3. On 22 May 2021, Mount Nyiragongo (Democratic Republic of the Congo), an open-vent volcano with a persistent lava lake perched within its summit crater, shook up this interpretation by producing an approximately six-hour-long flank eruption without apparent precursors, followed-rather than preceded-by lateral magma motion into the crust. Here we show that this reversed sequence was most likely initiated by a rupture of the edifice, producing deadly lava flows and triggering a voluminous 25-km-long dyke intrusion. The dyke propagated southwards at very shallow depth (less than 500 m) underneath the cities of Goma (Democratic Republic of the Congo) and Gisenyi (Rwanda), as well as Lake Kivu. This volcanic crisis raises new questions about the mechanisms controlling such eruptions and the possibility of facing substantially more hazardous events, such as effusions within densely urbanized areas, phreato-magmatism or a limnic eruption from the gas-rich Lake Kivu. It also more generally highlights the challenges faced with open-vent volcanoes for monitoring, early detection and risk management when a significant volume of magma is stored close to the surface.

Optimizing illumination for precise multi-parameter estimations in coherent diffractive imaging.

Coherent diffractive imaging (CDI) is widely used to characterize structured samples from measurements of diffracting intensity patterns. We introduce a numerical framework to quantify the precision that can be achieved when estimating any given set of parameters characterizing the sample from measured data. The approach, based on the calculation of the Fisher information matrix, provides a clear benchmark to assess the performance of CDI methods. Moreover, by optimizing the Fisher information metric using deep learning optimization libraries, we demonstrate how to identify the optimal illumination scheme that minimizes the estimation error under specified experimental constraints. This work paves the way for an efficient characterization of structured samples at the sub-wavelength scale.

Resampling the transmission matrix in an aberration-corrected Bessel mode basis.

The study of the optical transmission matrix (TM) of a sample reveals important statistics of light transport through it. The accuracy of the statistics depends strongly on the orthogonality and completeness of the basis in which the TM is measured. While conventional experimental methods suffer from sampling effects and optical aberrations, we use a basis of Bessel modes of the first kind to faithfully recover the singular values, eigenvalues and eigenmodes of light propagation through a finite thickness of air.

Optimal Control of Coherent Light Scattering for Binary Decision Problems.

Because of quantum noise fluctuations, the rate of error achievable in decision problems involving several possible configurations of a scattering system is subject to a fundamental limit known as the Helstrom bound. Here, we present a general framework to calculate and minimize this bound using coherent probe fields with tailored spatial distributions. As an example, we experimentally study a target located in between two disordered scattering media. We first show that the optimal field distribution can be directly identified using a general approach based on scattering matrix measurements. We then demonstrate that this optimal light field successfully probes the presence of the target with a number of photons that is reduced by more than 2 orders of magnitude as compared to unoptimized fields.

Femtosecond laser-ablation of gel and water.

We study the expansion dynamics of super-heated material during ultra-fast laser ablation of water and gel, using transient-reflectivity microscopy. We find that the expansion dynamics of water and gel, as observed during the first few nanoseconds, are extremely similar over a large range of ablation energies. We measure the crater topography of the gel after irradiation with a single laser shot, using optical interferometric microscopy, and estimate the mass that is ejected during the ablation. We calculate the laser energy deposited during irradiation by simulating the precise spatial distribution of the electron plasma density and temperature. We link the amount of removed mass obtained experimentally with the simulations of the deposited laser energy.

Optical method for micrometer-scale tracerless visualization of ultrafast laser induced gas flow at a water/air interface.

We study femtosecond-laser-induced flows of air at a water/air interface, at micrometer length scales. To visualize the flow velocity field, we simultaneously induce two flow fronts using two adjacent laser pump spots. Where the flows meet, a stationary shockwave is produced, the length of which is a measure of the local flow velocity at a given radial position. By changing the distance between the spots using a spatial light modulator, we map out the flow velocity around the pump spots. We find gas front velocities near the speed of sound in air vs for two laser excitation energies. We find an energy scaling that is inconsistent with the Sedov-Taylor model. Due to the flexibility offered by spatial beam shaping, our method can be applied to study subsonic laser-induced gas flow fronts in more complicated geometries.

Influence of the Local Scattering Environment on the Localization Precision of Single Particles.

We study the fundamental limit on the localization precision for a subwavelength scatterer embedded in a strongly scattering environment, using the external degrees of freedom provided by wavefront shaping. For a weakly scattering target, the localization precision improves with the value of the local density of states at the target position. For a strongly scattering target, the localization precision depends on the dressed polarizability that includes the backaction of the environment. This numerical study provides new insights for the control of the information content of scattered light by wavefront shaping, with potential applications in sensing, imaging, and nanoscale engineering.

Imaging through highly scattering environments using ballistic and quasi-ballistic light in a common-path Sagnac interferometer.

The survival of time-reversal symmetry in the presence of strong multiple scattering lies at the heart of some of the most robust interference effects of light in complex media. Here, the use of time-reversed light paths for imaging in highly scattering environments is investigated. A common-path Sagnac interferometer is constructed that is able to detect objects behind a layer of strongly scattering material at up to 14 mean free paths of total attenuation length. A spatial offset between the two light paths is used to suppress non-specific scattering contributions, limiting the signal to the volume of overlap. Scaling of the specific signal intensity indicates a transition from ballistic to quasi-ballistic contributions as the scattering thickness is increased. The characteristic frequency dependence for the coherent modulation signal provides a path length dependent signature, while the spatial overlap requirement allows for short-range 3D imaging. The technique of common-path, bistatic interferometry offers a conceptually novel approach that could open new applications in diverse areas such as medical imaging, machine vision, sensors, and lidar.

Cost-effectiveness of an educational healthcare circuit for bariatric surgery in France.

OBJECTIVES: An educational healthcare circuit (EHC) is proposed with the objective of preventing weight recovery of patients after bariatric surgery through education and lifestyle change. The objective of this study was to measure the viability of the EHC (shared medical appointments [SMAs] combined with bariatric surgery) through cost-effectiveness analysis. The EHC presented in this study is innovative because it offers a multidisciplinary approach based on medical, psychological and dietetic expertise to combat obesity. The strategy is to give the patient a diagnosis and then a personalised follow-up. STUDY DESIGN: A mathematical model based on a decision tree (1 year) and a Markov model (10 years) to measure the efficiency and cost of an EHC in comparison with the customary care offered in France were built. METHODS: The effects of the EHC were observed for the prevalence of type 2 diabetes and the risk of cardiovascular disease. The chosen financial perspective is from the point of view of the French social security system. RESULTS: The EHC records an incremental cost-effective ratio (ICER) of € 48,315.43 per quality-adjusted life year (QALY) over a 1-year horizon and € 28,283.77 per QALY over 10 years (with discount rate of 8%: € 25,362.85 per QALY). CONCLUSION: The results suggest that an EHC is more expensive yet more effective than usual care. That is, in the short term, the costs are high, but at 10 years, the treatment is cost-effective, representing a feasible alternative for those patients who qualify for bariatric surgery in France.

Adaptive Control of Necklace States in a Photonic Crystal Waveguide.

Resonant cavities with high quality factor and small mode volume provide crucial enhancement of light-matter interactions in nanophotonic devices that transport and process classical and quantum information. The production of functional circuits containing many such cavities remains a major challenge, as inevitable imperfections in the fabrication detune the cavities, which strongly affects functionality such as transmission. In photonic crystal waveguides, intrinsic disorder gives rise to high-Q localized resonances through Anderson localization; however their location and resonance frequencies are completely random, which hampers functionality. We present an adaptive holographic method to gain reversible control on these randomly localized modes by locally modifying the refractive index. We show that our method can dynamically form or break highly transmitting necklace states, which is an essential step toward photonic-crystal-based quantum networks and signal processing circuits, as well as slow light applications and fundamental physics.

Imaging of objects through a thin scattering layer using a spectrally and spatially separated reference.

Incoherently illuminated or luminescent objects give rise to a low-contrast speckle-like pattern when observed through a thin diffusive medium, as such a medium effectively convolves their shape with a speckle-like point spread function (PSF). This point spread function can be extracted in the presence of a reference object of known shape. Here it is shown that reference objects that are both spatially and spectrally separated from the object of interest can be used to obtain an approximation of the point spread function. The crucial observation, corroborated by analytical calculations, is that the spectrally shifted point spread function is strongly correlated to a spatially scaled one. With the approximate point spread function thus obtained, the speckle-like pattern is deconvolved to produce a clear and sharp image of the object on a speckle-like background of low intensity.

Finite-size Scaling of the Density of States in Photonic Band Gap Crystals.

The famous vanishing of the density of states (DOS) in a band gap, be it photonic or electronic, pertains to the infinite-crystal limit. In contrast, all experiments and device applications refer to finite crystals, which raises the question: Upon increasing the linear size L of a crystal, how fast does the DOS approach the infinite-crystal limit? We present a theory for finite crystals that includes Bloch-mode broadening due to the presence of crystal boundaries. Our results demonstrate that the DOS for frequencies inside a band gap has a 1/L scale dependence for crystals in one, two and three dimensions.

Observation After Cytoreductive Nephrectomy in Patients With Synchronous Not Completely Resected Metastases of Renal Cell Carcinoma.

OBJECTIVE: To determine the time-to-targeted therapy (TTT) in patients with not completely resected low-volume oligometastatic disease who were observed following debulking cytoreductive nephrectomy (CN) for metastatic renal cell carcinoma (mRCC). METHODS: Patients with synchronous mRCC with not completely resected low-volume metastases and in whom observation after CN was a multidisciplinary tumor board recommendation were identified from an approved institutional database. Patient data, International Metastatic Renal Cell Cancer Database Consortium (IMDC) risk, Fuhrman grade, site, and number of sites, time-to-progression (TTP), TTT, and overall survival (OS) were retrospectively analyzed. RESULTS: From 251 synchronous mRCC patients treated since 2006, 40 (15.9 %) were identified who underwent CN with observation as a result of low-volume multiple metastasis considered not completely resectable (19 single site and 21 with ≥2 sites). IMDC risk was favorable in 7, intermediate in 24, and poor in 9 patients. Median TTP was 6 (range 2-30) months and TTT was 16 (range 2-43) months. In 11 patients targeted therapy was further deferred by observation beyond Response Evaluation Criteria in Solid Tumors progression and in 10 patients by additional local therapy of the most rapidly progressing lesion. Median OS was 30 (range 2-71) months. CONCLUSION: In patients with synchronous mRCC and not completely resected low-volume metastasis, the TTT following CN was substantial. Local therapy to control the most rapidly progressing lesion or observation beyond progression was an additional means to defer systemic therapy.

Measurement of the linear thermo-optical coefficient of Ga0.51In0.49P using photonic crystal nanocavities.

Ga0.51In0.49P is a promising candidate for thermally tunable nanophotonic devices due to its low thermal conductivity. In this work we study its thermo-optical response. We obtain the linear thermo-optical coefficient dn/dT=2.0±0.3·10-4 K-1 by investigating the transmission properties of a single mode-gap photonic crystal nanocavity.

Tuning out disorder-induced localization in nanophotonic cavity arrays.

Weakly coupled high-Q nanophotonic cavities are building blocks of slow-light waveguides and other nanophotonic devices. Their functionality critically depends on tuning as resonance frequencies should stay within the bandwidth of the device. Unavoidable disorder leads to random frequency shifts which cause localization of the light in single cavities. We present a new method to finely tune individual resonances of light in a system of coupled nanocavities. We use holographic laser-induced heating and address thermal crosstalk between nanocavities using a response matrix approach. As a main result we observe a simultaneous anticrossing of 3 nanophotonic resonances, which were initially split by disorder.