Far-field radiation pattern in Coherent Anti-stokes Raman Scattering (CARS) Microscopy

Far field radiation pattern under tight focusing condition is investigated in Coherent Anti-stokes Raman Scattering (CARS) microscopy both in the forward (F-CARS) and backward (E-CARS) directions. While we assume no refraction index mismatch between the sample and the environing medium, our rigorous numerical electromagnetic computation takes into account the exact polarizations of the excitation laser beams and of the induced nonlinear dipoles. F-CARS and E-CARS radiation patterns, as well as their divergence, are studied as a function of the size of the sample object and compared to the excitation beams

Experimental violation of Tsirelson's bound by Maxwell fields

International audienceIn analogy with quantum optics it is possible to impose nonseparability between different degrees of freedom of an optical beam. The resulting correlations between these degrees of freedom can be investigated with correlations functions traditionally employed in quantum mechanics, such as the well-known Clauser-Horne-Shimony-Holt (CHSH) correlation function. In this paper we present results achieving a maximal violation of Tsirelson's bound on CHSH correlations between spatial and polarization degrees of freedom of classical (Maxwell) fields. We describe the theoretical method, based on the realization of a nonunitary gate, and then proceed to its experimental implementation carried out with classical optical techniques. Our approach relies on the realization at the level of classical Maxwell fields of a so-called POVM (positive operator valued measure) which is traditionally discussed in the realm of quantum physics

Axial localization of luminophores by partial coherence interferometry

We propose a solution for increasing the axial resolution of confocal microscopes. In the experimental set-up described in this paper an interference phenomenon between two counterpropagating beams is used to determine the axial position of a luminophore. The optical path difference between the two waves, which is related to the position of the luminophore, is recovered thanks to a second interferometer by using partial coherence interferometry demodulation technique. The proposed solution can find applications in biology for localizing with nanometric resolution a small number of tagged species

Increasing the lateral resolution of scanning microscopes by a factor of two using 2-Image microscopy

Increasing the resolution of optical microscopes is a challenging task for studying the cell machinery at the molecular level. 4Pi or TIRF microscopies permit one to reduce the axial dimension of the detection volume. To reduce its lateral dimension, we have proposed a solution in which the scanning head of a 4Pi microscope or of a confocal microscope is coupled to an interferometer. With this technique two beams coming from the source produce two images that are superimposed coherently. For this reason, one can call this technique 2-Image microscopy. It has been shown that with 2-Image microscopy, the complete use of the spatial frequencies collected by the objective allows to reach a 1.22 lambda/4NA lateral resolution. This improvement is independent of the excitation mode and is effective with incoherent light such as fluorescent or chemiluminescent (i.e. without optical excitation) samples. In this paper, we present an interferometric set-up and a modulation technique that make benefit fully from the advantages of 2-Image microscopy

4Pi-microscopie : Applications à la localisation axiale de luminophores et à l'amélioration de la résolution latérale

Ultra-sensitive, super-resolving and non invasive tools are required for studying the cell machinery at the molecular level. Thanks to the use of ultra-sensitive cameras and to the development of the 4PI-microscope, fluorescence microscopy technique is the best tool for this kind of study. Nevertheless, the axial localization of single molecules and the lateral resolution of the confocal microscopes must be improved. In our optical set-up, a 4Pi-microscope coupled to a Michelson interferometer allows to determine the axial position of a luminophore by Partial Coherence Interferometry (PCI). We have also proposed a configuration of 4Pi-microscopes for improving their lateral resolution.L'étude des mécanismes inter et intra-cellulaires nécessite d'utiliser des outils d'observation non invasifs pour la cellule, sensibles aux faibles signaux et très résolvants tant spatialement que temporellement. Actuellement, les techniques de microscopie à fluorescence réalisent le meilleur compromis entre ces trois caractéristiques, notamment grâce à l'apparition de caméras ultrasensibles et du 4Pi-microscope. Néanmoins, la localisation axiale de molécules individuelles et la résolution latérale des microscopes confocaux doivent être encore améliorées. Le couplage d'un 4Pi-microscope et d'un interféromètre de Michelson, nous a permis de localiser axialement des luminophores par interférométrie à faible longueur de cohérence. Nous avons également proposé une modification des 4Pi-microscopes afin d'améliorer leur résolution latérale

Increasing the lateral resolution of 4Pi fluorescence microscopes

7 pagesThe axial resolution of fluorescence microscopes can be considerably improved by superposing two illumination beams and by adding coherently the two wavefronts emitted by the luminescent sample. This solution has been implemented in 4Pi microscopes. Theoretical and experimental results have shown that a considerable improvement of the axial resolution can be obtained with these microscopes. However, the lateral resolution remains limited by diffraction. We propose a configuration of a 4Pi microscope in which the lateral displacement of the source modify the Collection Efficiency Function (CEF). Numerical calculations based on an approximated scalar theory and on exact vector-wave-optics results of the field distribution of the electromagnetic field in image space, show that the lateral extent of the CEF can be reduced by a factor greater than two with respect to the diffraction limit. We show that, with this solution, the resolution in the transverse plane of 4Pi type B and 4Pi type C microscopes can be improved significantly