Single-emitter super-resolved imaging of radiative decay rate enhancement in dielectric gap nanoantennas Córdova-Castro, R. M., B. Van Dam, A. Lauri, S. A. Maier, R. Sapienza, Y. De Wilde, I. Izeddin, and V. Krachmalnicoff Light: Science and Applications 13, no. 1 (2024)
Résumé: High refractive index dielectric nanoantennas strongly modify the decay rate via the Purcell effect through the design of radiative channels. Due to their dielectric nature, the field is mainly confined inside the nanostructure and in the gap, which is hard to probe with scanning probe techniques. Here we use single-molecule fluorescence lifetime imaging microscopy (smFLIM) to map the decay rate enhancement in dielectric GaP nanoantenna dimers with a median localization precision of 14 nm. We measure, in the gap of the nanoantenna, decay rates that are almost 30 times larger than on a glass substrate. By comparing experimental results with numerical simulations we show that this large enhancement is essentially radiative, contrary to the case of plasmonic nanoantennas, and therefore has great potential for applications such as quantum optics and biosensing.
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Real-time acousto-optic imaging using high-peak-power long-pulsed illumination Figliolia, F., Q. Liu, S. Janicot, P. Georges, G. Lucas-Leclin, J. P. Huignard, F. Ramaz, J. M. Tualle, and M. Bocoum Optics Letters 49, no. 21, 5993-5996 (2024)
Résumé: Acousto-optic imaging (AOI) of absorbing objects embedded in highly scattering media remains challenging, since the detectable signal suitable for image reconstruction is weak. To increase the detected signals to a level required by live biological applications, we designed a high-peak-power quasi-continuous laser source based on the coherent combination of two pulsed amplifiers, delivering 100-µs-long pulses with a 9 W peak power at a 100 Hz repetition rate while maintaining an average power below 100 mW; jointly used with a digital holographic detection that maximizes the amount of collected signal, we demonstrate for the first time to our knowledge the optical imaging of 2-cm-thick highly scattering media (µs′ ∼ 10 cm−1) at near-video frame rate (0.2 Hz) using the Fourier transform-AOI.
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Multi-spectral reflection matrix for ultrafast 3D label-free microscopy Balondrade, P., V. Barolle, N. Guigui, E. Auriant, N. Rougier, C. Boccara, M. Fink, and A. Aubry Nature Photonics 18, no. 10, 1097-1104 (2024)
Résumé: Label-free microscopy exploits light scattering to obtain a three-dimensional image of biological tissues. However, light propagation is affected by aberrations and multiple scattering, which drastically degrade the image quality and limit the penetration depth. Multi-conjugate adaptive optics and time-gated matrix approaches have been developed to compensate for aberrations but the associated frame rate is extremely limited for three-dimensional imaging. Here we develop a multi-spectral matrix approach to solve these fundamental problems. On the basis of a sparse illumination scheme and an interferometric measurement of the reflected wave field at multiple wavelengths, the focusing process can be optimized in post-processing for any voxel by addressing independently each frequency component of the reflection matrix. A proof-of-concept experiment shows a three-dimensional image of an opaque human cornea over a 0.1 mm3 field of view at a 290 nm resolution and a 1 Hz frame rate. This work paves the way towards a fully digital microscope allowing real-time, in vivo, quantitative and deep inspection of tissues.
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Aberration compensation in Doppler holography of the human eye fundus by subaperture signal correlation Bratasz, Z., O. Martinache, J. Sverdlin, D. Gatinel, and M. Atlan Biomedical Optics Express 15, no. 10, 5660-5673 (2024)
Résumé: The process of obtaining images of capillary vessels in the human eye’s fundus using Doppler holography encounters difficulties due to ocular aberrations. To enhance the accuracy of these images, it is advantageous to apply an adaptive aberration correction technique. This study focuses on numerical Shack-Hartmann, which employs sub-pupil correlation as the wavefront sensing method. Application of this technique to Doppler holography encounters unique challenges due to the holographic detection properties. A detailed comparative analysis of the regularization technique against direct gradient integration in the estimation of aberrations is made. Two different reference images for the measurement of image shifts across subapertures are considered. The comparison reveals that direct gradient integration exhibits greater effectiveness in correcting asymmetrical aberrations.
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