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

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

Signatures of exciton coupling in paired nanoemitters

An exciton formed by the delocalized electronic excitation of paired nanoemitters is interpreted in terms of the electromagnetic emission of the pair and their mutual coupling with a photodetector. A formulation directly tailored for fluorescence detection is identified, giving results which are strongly dependent on geometry and selection rules. Signature symmetric and antisymmetric combinations are analyzed and their distinctive features identified

A functional variant in the Stearoyl-CoA desaturase gene promoter enhances fatty acid desaturation in pork

There is growing public concern about reducing saturated fat intake. Stearoyl-CoA desaturase (SCD) is the lipogenic enzyme responsible for the biosynthesis of oleic acid (18:1) by desaturating stearic acid (18:0). Here we describe a total of 18 mutations in the promoter and 3′ non-coding region of the pig SCD gene and provide evidence that allele T at AY487830:g.2228T>C in the promoter region enhances fat desaturation (the ratio 18:1/18:0 in muscle increases from 3.78 to 4.43 in opposite homozygotes) without affecting fat content (18:0+18:1, intramuscular fat content, and backfat thickness). No mutations that could affect the functionality of the protein were found in the coding region. First, we proved in a purebred Duroc line that the C-T-A haplotype of the 3 single nucleotide polymorphisms (SNPs) (g.2108C>T; g.2228T>C; g.2281A>G) of the promoter region was additively associated to enhanced 18:1/18:0 both in muscle and subcutaneous fat, but not in liver. We show that this association was consistent over a 10-year period of overlapping generations and, in line with these results, that the C-T-A haplotype displayed greater SCD mRNA expression in muscle. The effect of this haplotype was validated both internally, by comparing opposite homozygote siblings, and externally, by using experimental Duroc-based crossbreds. Second, the g.2281A>G and the g.2108C>T SNPs were excluded as causative mutations using new and previously published data, restricting the causality to g.2228T>C SNP, the last source of genetic variation within the haplotype. This mutation is positioned in the core sequence of several putative transcription factor binding sites, so that there are several plausible mechanisms by which allele T enhances 18:1/18:0 and, consequently, the proportion of monounsaturated to saturated fat.This research was supported by grants from the Spanish Ministry of Science and Innovation (AGL2009-09779 and AGL2012-33529). RRF is recipient of a PhD scholarship from the Spanish Ministry of Science and Innovation (BES-2010-034607). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of manuscript

Near field dielectric microlenses

International audienceThe electromagnetic backscattered response of a metallic nanoparticle located close to a dielectric microsphere illuminated by a plane wave or a focused beam is theoretically investigated. It is demonstrated that the main contribution of the microsphere consists in increasing the excitation field. Furthermore, investigation of dipolar emission close to the microsphere shows a redirection of the radiated field in the backward direction

Straightforward control of light in a metallic trimer

International audienceA trimer of gold particles 50 nm in diameter is illuminated in oblique incidence by a plane wave. It is shown that one can fully focus light in only one nanogap and that the localization of the hot spot between the two nanogaps is controlled via the angle of incidence of the illuminating plane wave. The physical mechanism of this surprising phenomenon is unveiled. It relies on the excitation of opposite and in phase modes. Furthermore, balancing of the fundamental modes of the system permits to extinguish the dipolar moment of a metallic particle

Mode-balancing far-field control of light localization in nanoantennas

International audienceLight localization is controlled at a scale of lambda/10 in the harmonic regime from the far-field domain in a plasmonic nanoantenna.The nanoantenna under study consists of three aligned spheres 50 nm in diameter separated by a distance of 5 nm. By simply tuning the orientation of an incident plane wave, symmetric and antisymmetric mode balancing induces a strong enhancement of the near-field intensity in one nanogap while nullifying the light intensity in the other nanogap. Furthermore, it is demonstrated that the dipolar moment of a plasmonic particle can be fully extinguished when strongly coupled with a dimer of identical nanoparticles

Photonic jets and Bessel beams

International audiencePhotonic jets can be produced by the illumination of a micrometer dielectric particle by an optical plane wave, and are characterized by a narrow elongated focal volume. Bessel beams have been widely studied in recent decades and are commonly referred to as being "diffractionless" over long distances. The Bessel beam aspects of photonic jets are investigated in this manuscript. In particular, we show that photonic jets take their properties from Bessel propagative beams, but more complex phenomena are involved