Photon Echo and Single Molecule Fluorescence Measurements of Organic Dyes in Thin Polymer Films
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2003
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Swarthmore College. Dept. of Physics & Astronomy
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Thesis (B.A.)
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en_US
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Full copyright to this work is retained by the student author. It may only be used for non-commercial, research, and educational purposes. All other uses are restricted.
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Abstract
The extraordinarily short optical dephasing time of organic dye molecules in polymer hosts is known to be under 20 fs between 100 and 200 K. Short dephasing times suggest enormously broadened homogeneous linewidths on the order of 10 nm. Direct observation of single dye molecule fluorescence spectra shows a similarly broadened line, giving comparable dephasing times for room temperature measurements. While this single molecule linewidth agrees with that of the bulk sample, it is inaccurate to attribute this broadening to homogeneous mechanisms. Repeated single molecule fluorescence measurements permit determination of the homogeneous nature of this linewidth, as distinct from the inhomogeneous nature of dispersion in bulk samples. Spectral diffusion in single molecule spectra is evidenced by multiple peaks, visible despite broad spectra lines at room temperature. In the particular experiment discussed in this thesis, fluorescence from single organic dye molecules in thin polymethyl methacrylate films was studied with scanning confocal microscopy. Photon antibunching exhibited by the photon-pair correlation function g(2) (τ) at τ = 0 confirms that single molecule emission spectra were obtained.