Spontaneous Raman microscopy is well-known for its remarkable chemical contrast yet suffers from slow acquisition speeds. Recently, the compressive Raman microspectroscopy framework has shown that a significant speed advantage is brought by leveraging shot-noise-limited detection using a single-photon avalanche diode (SPAD). However, current imaging speeds of compressive Raman architectures are fundamentally limited by SPAD sensitivity and dead time. Here, we demonstrate an efficient and scalable compressive Raman parallelization scheme based on SPAD arrays. We show that parallelization using line excitation, instead of spatial multiplexing, allows to reach effective pixel dwell times (τ pdt ) of 0.8 µs. Such fast speed represents over one order-of-magnitude speed-up over previous demonstrations. This effective parallelization not only allows for demonstrating unprecedented chemical imaging speeds using the otherwise weak spontaneous Raman effect but also paves the way for true video-rate inexpensive molecular microspectroscopy.

Many processes in microfluidics and biology are driven or affected by viscosity. While several methods are able to measure this parameter globally, very few can provide high resolution viscosity images. Optimizing the locality of viscosity measurements demands smaller probes but also shorter lateral diffusion lengths and measurement times. Here, we propose to use sub-micrometer magnetic rods to perform high resolution viscosity imaging. An external magnetic field forces the oscillation of superparamagnetic iron oxide rods. Under linearly polarized illumination, the rotation of these highly anisotropic optical scatterers induces a blinking which is analyzed by heterodyne holography. The spectral analysis of the rotation dynamics yields a regime transition frequency from which the local viscosity is deduced. Holography provides a 3D optical field reconstruction and 3D superlocalization of the rods, which allows super-resolved viscosity measurements. Relying on the fast Brownian rotation instead of the slower translation component of nanorods therefore allows faster measurements and, crucially, smaller effective voxels for viscosity determination. We thus demonstrate that viscosity imaging is possible with a 0.5 (micron)^3 3D-resolution.

Quantitative phase imaging enables precise and label-free characterizations of individual nano-objects within a large volume, without a priori knowledge of the sample or imaging system. While emerging common path implementations are simple enough to promise a broad dissemination, their phase sensitivity still falls short of precisely estimating the mass or polarizability of vesicles, viruses, or nanoparticles in single-shot acquisitions. In this paper, we revisit the Zernike filtering concept, originally crafted for intensity-only detectors, with the aim of adapting it to wavefront imaging. We demonstrate, through numerical simulation and experiments based on high-resolution wavefront sensing, that a simple Fourier-plane add-on can significantly enhance phase sensitivity for subdiffraction objects & horbar;achieving over an order of magnitude increase (x12)& horbar;while allowing the quantitative retrieval of both intensity and phase. This advancement allows for more precise nano-object detection and metrology.

Tandis qu’une image classique reproduit l’aspect visuel d’une scène, l’imagerie hyperspectrale peut en révéler d’autres facettes cachées. Il s’agit d’un moyen de sonder, sans contact, des objets physiquement inaccessibles dans une dimension supplémentaire. Néanmoins, cette augmentation de dimensionnalité s’accompagne d’obstacles : la lenteur et le volume des données générées par ces méthodes constituaient jusqu’alors une limitation cruciale pour les applications nécessitant un haut débit. Des avancées récentes ont cependant permis de réaliser des observations spatio-spectrales en temps réel, telles que des cartographies dynamiques de la composition chimique d’échantillons vivants.

Compressive Raman imaging has emerged as a promising technique to speed up chemical imaging by compressing the data during acquisition. Yet, current scanning imaging speed is fundamentally limited by the sensors pixel dwell times of at best 1 µs. Here, we introduce a compressive Raman spectrometer layout equipped with a novel parallelized spatial acquisition using a single-photon avalanche detector array. We show imaging with pixel dwell times of <10µs using the otherwise weak spontaneous Raman effect, thereby reaching real-time imaging.

We demonstrate an efficient and scalable compressive Raman parallelization scheme based on single-photon avalanche diode (SPAD) arrays to reach pixel dwell times of 23 $\mu$s, representing over 10$\times$ speed-up using the otherwise weak spontaneous Raman effect.

We report on the use of a thin diffuser placed in the close vicinity of a camera sensor as a simple and effective way to superlocalize plasmonic nanoparticles in 3D. This method is based on holographic reconstruction via quantitative phase and intensity measurements of a light field after its interaction with nanoparticles. We experimentally demonstrate that this thin diffuser can be used as a simple add-on to a standard bright-field microscope to allow the localization of 100 nm gold nanoparticles at video rate with nanometer precision (1.3 nm laterally and 6.3 nm longitudinally). We exemplify the approach by revealing the dynamic Brownian trajectory of a gold nanoparticle trapped in various pockets within an agarose gel. The proposed method provides a simple but highly performant way to track nanoparticles in 3D.

By measuring the blinking induced by nanorods either in active (magnetically forced) or passive (Brownian) rotation with heterodyne holography, we performed high resolution viscosity imaging, an essential tool to study many microfluidic and biological processes.

Under polarized illumination, non-spherical objects display anisotropic scattering, and their rotation induces a blinking. We present a method based on heterodyne holography to measure images of the Brownian rotation frequencies of gold nanorods over a broad frequency range (0-10 MHz). Since Brownian rotation often occurs on shorter space and time scales than translation, it can provide local viscosity measurements, and high resolution imaging is possible. Here, we demonstrate that viscosity contrast imaging is revealed by heterodyne imaging at one or several investigation frequencies. After calibration, a frequency scan can give access to quantitative viscosity imaging.

1 Sorbonne Université, CNRS, INSERM, Institut de la Vision, 17 Rue Moreau, F-75012 Paris, France. 2 Holographic Microscopy Group, Neurophotonics Laboratory, UMR 8250 CNRS, University Paris Descartes, 45 rue des Saints-Pères, 75006 Paris, France. 3 Center for Interdisciplinary Research in Biology, Collège de France, UMR 7241 CNRS, U1050 INSERM, Equipe Labellisée FRM, Paris, France. E-mail: gilles.tessier@sorbonne-universite.fr