Time resolved fluorescence polarization measurements for entire emission spectra with a resistive-anode, single-photon-counting detector: the Fluorescence Omnilyzer. Lisa A. Kelly, John G. Trunk, and John C. Sutherland Rev. Sci. Instr. 68(6), 2279-2286 (1997). Abstract: We report a fluorescence analyzer that records simultaneously the temporal profiles for both orthogonal linear polarizations for all wavelengths in a fluorescence emission spectrum. The Analyzer combines a resistive-anode single-photon-counting photomultiplier, imaging spectrograph, Wollaston polarizer, multiparameter analyzer with histogramming memory and standard timing electronics.

The spectrograph disperses the fluorescence spectrum across the photocathode of the photomultiplier, and the Wollaston polarizer separates the spectra of the two polarizations in opposite directions from the center of the photocathode perpendicular to the direction of spectral dispersion. The locations at which each photon reaches the photocathode is determined by the ratios of the charges read from the four corners of the resistive-anode. One of the two address coordinates that determine where in histogramming memory each photon is recorded is obtained by measuring the time-of-arrival of the photon at the detector relative to the pulse of light that excites the fluorescence. The second address coordinate is obtained by combining the most-significant bit of the location of the event along the direction on the resistive anode corresponding to the polarization of the photon with the multi-bit digital value indicating photon wavelength. Storing the data directly into histogramming memory permits display of the data-set as it is recorded. Both the spectral and temporal calibrations of the fluorescence analyzer are independent of the polarization of the fluorescence. The ~100 ps temporal resolution of the resistive-anode detector is well matched to the ~1 ns FWHM pulses of light produced by the synchrotron storage ring that we use as the excitation source, but laser excitation could also be used with this detector.

Denise Monteleone operates the Omnilyzer at NSLS beamline U9B.

Color map of the wavelength-time-polarization resolved emmission spectrum of the single tryptophane in the outer surface protein A of the spirochete Borrelia burgdorferi, the etiological agent of Lyme disease. The perpendicularly polarized component of the fluorescence is less intense than the parallel polarized component, indicating that the tryptophane cannot rotate freely during the ~1.1 ns lifetime of the excited singlet state. Intensity measurements of the two polarization components as a function of time permits determination of the rotational correlation time of the tryptophane. To view the full, annotated spectrum click on icon.

Pulsed light from the synchrotron passes through a Glan-Thompson polarizer, Pgt, and is focused on the sample, S. Fluorescence is collected by an off-axis ellipsoidal mirror, Me, and, after reflection from a plane mirror, Mp, passes through a Wollaston polarizer, Pw, before reaching a focus on the entrance slit of the imaging spectrograph. To view a full size optical diagram and electronic schematic of the Omnilyzer click on icon.

R&D Magazine selected the Omnilyzer as one of the 100 most important technical developments of 1997. Read about this recognition in the BNL Press Release, and in the Brookhaven Bulletin Vol.51 No.39 of October 3, 1997.

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