195 research outputs found

    Indistinguishable Photons from a Single Molecule

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    We report the results of coincidence counting experiments at the output of a Michelson interferometer using the zero-phonon-line emission of a single molecule at 1.4K1.4 K. Under continuous wave excitation, we observe the absence of coincidence counts as an indication of two-photon interference. This corresponds to the observation of Hong-Ou-Mandel correlations and proves the suitability of the zero-phonon-line emission of single molecules for applications in linear optics quantum computation.Comment: To appear in Phys. Rev. Let

    Subnanosecond spectral diffusion measurement using photon correlation

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    Spectral diffusion is a result of random spectral jumps of a narrow line as a result of a fluctuating environment. It is an important issue in spectroscopy, because the observed spectral broadening prevents access to the intrinsic line properties. However, its characteristic parameters provide local information on the environment of a light emitter embedded in a solid matrix, or moving within a fluid, leading to numerous applications in physics and biology. We present a new experimental technique for measuring spectral diffusion based on photon correlations within a spectral line. Autocorrelation on half of the line and cross-correlation between the two halves give a quantitative value of the spectral diffusion time, with a resolution only limited by the correlation set-up. We have measured spectral diffusion of the photoluminescence of a single light emitter with a time resolution of 90 ps, exceeding by four orders of magnitude the best resolution reported to date

    Fourth order indirect integration method for black hole perturbations: even modes

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    On the basis of a recently proposed strategy of finite element integration in time domain for partial differential equations with a singular source term, we present a fourth order algorithm for non-rotating black hole perturbations in the Regge-Wheeler gauge. Herein, we address even perturbations induced by a particle plunging in. The forward time value at the upper node of the (r,t)(r^*,t) grid cell is obtained by an algebraic sum of i) the preceding node values of the same cell, ii) analytic expressions, related to the jump conditions on the wave function and its derivatives, iii) the values of the wave function at adjacent cells. In this approach, the numerical integration does not deal with the source and potential terms directly, for cells crossed by the particle world line. This scheme has also been applied to circular and eccentric orbits and it will be object of a forthcoming publication.Comment: This series of papers deals with EMRI for LISA. With the respect to the v1 version, the algorithm has been improved; convergence tests and references have been added; v2 is composed by 23 pages, and 6 figures. Paper accepted by Class. Quantum Gravity for the special issue on Theory Meets Data Analysis at Comparable and Extreme Mass Ratios (Capra and NRDA) at Perimeier Institute in June 201

    Tips for implementing multigrid methods on domains containing holes

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    As part of our development of a computer code to perform 3D `constrained evolution' of Einstein's equations in 3+1 form, we discuss issues regarding the efficient solution of elliptic equations on domains containing holes (i.e., excised regions), via the multigrid method. We consider as a test case the Poisson equation with a nonlinear term added, as a means of illustrating the principles involved, and move to a "real world" 3-dimensional problem which is the solution of the conformally flat Hamiltonian constraint with Dirichlet and Robin boundary conditions. Using our vertex-centered multigrid code, we demonstrate globally second-order-accurate solutions of elliptic equations over domains containing holes, in two and three spatial dimensions. Keys to the success of this method are the choice of the restriction operator near the holes and definition of the location of the inner boundary. In some cases (e.g. two holes in two dimensions), more and more smoothing may be required as the mesh spacing decreases to zero; however for the resolutions currently of interest to many numerical relativists, it is feasible to maintain second order convergence by concentrating smoothing (spatially) where it is needed most. This paper, and our publicly available source code, are intended to serve as semi-pedagogical guides for those who may wish to implement similar schemes.Comment: 18 pages, 11 figures, LaTeX. Added clarifications and references re. scope of paper, mathematical foundations, relevance of work. Accepted for publication in Classical & Quantum Gravit

    Electronically preresonant stimulated Raman scattering microscopy in the visible

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    We report an experimental scheme for stimulated Raman scattering (SRS) microscopy with excitation in the visible spectral region. This allows electronically preresonant (epr) SRS microscopy of a broad range of chromophores with sensitivities as low as 1 μM. Our experiment is based on two synchronously near-infrared pumped optical parametric oscillators (OPO). One of the outputs is modulated at a fourth of the repetition rate with a novel broadband electro-optical modulator. Using a combination of spectral focusing and tuning of the OPO, we show the recording of epr-SRS spectra over the whole range of molecular vibrations at a speed up to 20 times faster than classical wavelength tuning. The imaging capabilities of this setup are demonstrated with material scientific and cellular samples

    Label-free chemically specific imaging in planta with stimulated Raman scattering microscopy.

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    The growing world population puts ever-increasing demands on the agricultural and agrochemical industries to increase agricultural yields. This can only be achieved by investing in fundamental plant and agrochemical research and in the development of improved analytical tools to support research in these areas. There is currently a lack of analytical tools that provide noninvasive structural and chemical analysis of plant tissues at the cellular scale. Imaging techniques such as coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS) microscopy provide label-free chemically specific image contrast based on vibrational spectroscopy. Over the past decade, these techniques have been shown to offer clear advantages for a vast range of biomedical research applications. The intrinsic vibrational contrast provides label-free quantitative functional analysis, it does not suffer from photobleaching, and it allows near real-time imaging in 3D with submicrometer spatial resolution. However, due to the susceptibility of current detection schemes to optical absorption and fluorescence from pigments (such as chlorophyll), the plant science and agrochemical research communities have not been able to benefit from these techniques and their application in plant research has remained virtually unexplored. In this paper, we explore the effect of chlorophyll fluorescence and absorption in CARS and SRS microscopy. We show that with the latter it is possible to use phase-sensitive detection to separate the vibrational signal from the (electronic) absorption processes. Finally, we demonstrate the potential of SRS for a range of in planta applications by presenting in situ chemical analysis of plant cell wall components, epicuticular waxes, and the deposition of agrochemical formulations onto the leaf surface

    Diffraction techniques and vibrational spectroscopy opportunities to characterise bones

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    From a histological point of view, bones that allow body mobility and protection of internal organs consist not only of different organic and inorganic tissues but include vascular and nervous elements as well. Moreover, due to its ability to host different ions and cations, its mineral part represents an important reservoir, playing a key role in the metabolic activity of the organism. From a structural point of view, bones can be considered as a composite material displaying a hierarchical structure at different scales. At the nanometre scale, an organic part, i.e. collagen fibrils and an inorganic part, i.e. calcium phosphate nanocrystals are intimately mixed to assure particular mechanical properties
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