Spectral analysis of three-dimensional photonic jets

International audienceThe spatial and spectral properties of three-dimensional photonic jets are studied in a framework employing rigorous Lorentz-Mie theory. The contributions to the field from each spectral component are studied quantitatively and highlight the distinctive features of photonic jets. In particular, the presence of secondary lobes in the propagative frequency distribution are singled out as a fundamental distinctive property between photonic jets and classical Gaussian beams. It is shown that these differences can lead to divergences of photonic jets at least twice as small as those in corresponding ‘Gaussian' beams

Ultracompact and unidirectional metallic antennas

International audienceWe investigate the angular redistribution of light radiated by a single emitter located in the vicinity of dipolar silver nanoparticles. We point out the fundamental role of the phase differences introduced by the optical path difference between the emitter and the particle and demonstrate that the polarizability of the metallic nanoparticle alone cannot predict the emission directionality. In particular, we show that collective or reflective properties of single nanoparticles can be controlled by tuning the distance of a single emitter at a λ/30 scale. These results enable us to design unidirectional and ultracompact nanoantennas composed of just two coupled nanoparticles separated by a distance achievable with biological linkers

In vivo imaging of pyrrole-imidazole polyamides with positron emission tomography

The biodistribution profiles in mice of two pyrrole-imidazole polyamides were determined by PET. Pyrrole-imidazole polyamides are a class of small molecules that can be programmed to bind a broad repertoire of DNA sequences, disrupt transcription factor-DNA interfaces, and modulate gene expression pathways in cell culture experiments. The 18F-radiolabeled polyamides were prepared by oxime ligation between 4-[18F]-fluorobenzaldehyde and a hydroxylamine moiety at the polyamide C terminus. Small animal PET imaging of radiolabeled polyamides administered to mice revealed distinct differences in the biodistribution of a 5-ring β-linked polyamide versus an 8-ring hairpin, which exhibited better overall bioavailability. In vivo imaging of pyrrole-imidazole polyamides by PET is a minimum first step toward the translation of polyamide-based gene regulation from cell culture to small animal studies

Direct imaging of photonic nanojets

International audienceWe report the direct experimental observation of photonic nanojets created by single latex microspheres illuminated by a plane wave at a wavelength of 520 nm. Measurements are performed with a fast scanning confocal microscope in detection mode, where the detection pinhole defines a diffraction-limited observation volume that is scanned in three dimensions over the microsphere vicinity. From the collected stack of images, we reconstruct the full 3 dimensional photonic nanojet beam. Observations are conducted forpolystyrene spheres of 1, 3 and 5 mum diameter deposited on a glass substrate, the upper medium being air or water. Experimental results are compared to calculations performed using the Mie theory. We measure nanojet sizes as small as 270 nm FWHM for a 3 mum sphere at a wavelength lambda of 520 nm. The beam keeps a subwavelength FWHM over a propagation distance of more than 3 lambda, displaying all the specificities of a photonic nanojet