Imaging the three-dimensional scattering pattern of plasmonic nanodisk chains by digital heterodyne holography

Quantitative Temperature Measurements in Gold Nanorods Using Digital Holography

Temperature characterization and quantification at the nanoscale remain core challenges in applications based on photoinduced heating of nanoparticles. Here, we propose a new approach to obtain quantitative temperature measurements on individual nanoparticles by combining modulated photothermal stimulation and heterodyne digital holography. From full-field reconstructed holograms, the temperature is determined with a precision of 0.3 K via a simple approach without requiring any calibration or fitting parameters. As an application, the dependence of temperature on the aspect ratio of gold nanoparticles is investigated. A good agreement with numerical simulation is observed.

Quantifying single plasmonic nanostructure far-fields with interferometric and polarimetric k-space microscopy

Optically resonant nanoantennae are key building blocks for metasurfaces, nanosensors, and nanophotonic light sources due to their ability to control the amplitude, phase, directivity, and polarization of scattered light. Here, we report an experimental technique for the full recovery of all degrees of freedom encoded in the far-field radiated by a single nanostructure using a high-NA Fourier microscope equipped with digital off-axis holography. This method enables full decomposition of antenna-physics in its multipole contributions and gives full access to the orbital and spin angular momentum properties of light scattered by single nano-objects. Our results demonstrate these capabilities through a quantitative assessment of the purity of the "selection rules" for orbital angular momentum transfer by plasmonic spiral nanostructures.

Wrapping-free numerical refocusing of scalar electromagnetic fields

Numerical refocusing in any plane is one powerful feature granted by measuring both the amplitude and the phase of a coherent light beam. Here, we introduce a method based on the first Rytov approximation of scalar electromagnetic fields that (i) allows numerical propagation without requiring phase unwrapping after propagation and (ii) limits the effect of artificial phase singularities that appear upon numerical defocusing when the measurement noise is mixing with the signal. We demonstrate the feasibility of this method with both scalar electromagnetic field simulations and real acquisitions of microscopic biological samples imaged at high numerical aperture.

Self-interference 3D super-resolution microscopy for deep tissue investigations

Fluorescence localization microscopy has achieved near-molecular resolution capable of revealing ultra-structures, with a broad range of applications, especially in cellular biology. However, it remains challenging to attain such resolution in three dimensions and inside biological tissues beyond the first cell layer. Here we introduce SELFI, a framework for 3D single-molecule localization within multicellular specimens and tissues. The approach relies on self-interference generated within the microscope's point spread function (PSF) to simultaneously encode equiphase and intensity fluorescence signals, which together provide the 3D position of an emitter. We combined SELFI with conventional localization microscopy to visualize F-actin 3D filament networks and reveal the spatial distribution of the transcription factor OCT4 in human induced pluripotent stem cells at depths up to 50 µm inside uncleared tissue spheroids. SELFI paves the way to nanoscale investigations of native cellular processes in intact tissues.

Acousto-optic wide band optical low-frequency shifter

A wide bandwidth tunable optical low-frequency shifter is presented in this work. It is based on two acousto-optic devices operating in tandem. The relevant parameters of the specific configurations of acousto-optic interactions in paratellurite material are detailed. Results from numerical computations leading to the practical design parameters are given. The low-frequency shifter has been experimentally tested at a visible wavelength λ₀=514  nm and a high efficiency (>60%) has been measured. The tuning capability of the optical shifter covers a bandwidth Δf=26  MHz.

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.