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Start date: 2020 × Subject: Dispersions ×

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Now showing 1 - 3 of 3
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    Exciton dispersion in para-quaterphenyl: Significant molecular interactions beyond Coulomb coupling
    (New York, NY : American Inst. of Physics, 2021) Graf, Lukas; Krupskaya, Yulia; Büchner, Bernd; Knupfer, Martin
    We have experimentally determined the momentum dependence of the electronic excitation spectra of para-quaterphenyl single crystals. The parallel arrangement of para-quaterphenyl molecules results in a strong Coulomb coupling of the molecular excitons. Such crystals have been considered to be a very good realization of the Frenkel exciton model, including the formation of H-type aggregates. Our data reveal an unexpected exciton dispersion of the upper Davydov component, which cannot be rationalized in terms of inter-molecular Coulomb coupling of the excitons. A significant reduction of the nearest neighbor coupling due to additional charge-transfer processes is able to provide an explanation of the data. Furthermore, the spectral onset of the excitation spectrum, which represents a heavy exciton resulting from exciton-phonon coupling, also shows a clear dispersion, which had been unknown so far. Finally, an optically forbidden excitation about 1 eV above the excitation onset is observed. © 2021 Author(s).
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    Milliradian precision ultrafast pulse control for spectral phase metrology
    (Washington, DC : Soc., 2021) Stamm, Jacob; Benel, Jorge; Escoto, Esmerando; Steinmeyer, Günter; Dantus, Marcos
    A pulse-shaper-based method for spectral phase measurement and compression with milliradian precision is proposed and tested experimentally. Measurements of chirp and third-order dispersion are performed and compared to theoretical predictions. The single-digit milliradian accuracy is benchmarked by a group velocity dispersion measurement of fused silica.
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    First stellar photons for an integrated optics discrete beam combiner at the William Herschel Telescope
    (Washington, DC : The Optical Society, 2021) Nayak, Abani Shankar; Labadie, Lucas; Sharma, Tarun Kumar; Piacentini, Simone; Corrielli, Giacomo; Osellame, Roberto; Gendron, Éric; Buey, Jean-Tristan M.; Chemla, Fanny; Cohen, Mathieu; Bharmal, Nazim A.; Bardou, Lisa F.; Staykov, Lazar; Osborn, James; Morris, Timothy J.; Pedretti, Ettore; Dinkelaker, Aline N.; Madhav, Kalaga V.; Roth, Martin M.
    We present the first on-sky results of a four-telescope integrated optics discrete beam combiner (DBC) tested at the 4.2mWilliamHerschel Telescope. The device consists of a four-input pupil remapper followed by a DBC and a 23-output reformatter. The whole device was written monolithically in a single alumino-borosilicate substrate using ultrafast laser inscription. The device was operated at astronomical H-band (1.6 μm), and a deformable mirror along with a microlens array was used to inject stellar photons into the device. We report the measured visibility amplitudes and closure phases obtained on Vega and Altair that are retrieved using the calibrated transfer matrix of the device. While the coherence function can be reconstructed, the on-sky results show significant dispersion from the expected values. Based on the analysis of comparable simulations, we find that such dispersion is largely caused by the limited signal-to-noise ratio of our observations. This constitutes a first step toward an improved validation of theDBCas a possible beam combination scheme for long-baseline interferometry. © 2021 Optical Society of America.