Selected Publications

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By Michael Ware (et al.)
Abstract: We discuss a practical implementation of a photon-counting detector calibration using correlated photon pairs produced by parametric down-conversion. In this calibration scheme, the detection of a first photon triggers the measurement sequence aimed at detection of a second photon by a detector under test (DUT). We also describe measurements of radiant power with a photon-counting detector, which is important for implementation of a conventional calibration technique based on detector substitution. In the experiment, we obtain a time-delay histogram of DUT detection events consisting of a correlated signal and a background. We present a method for separating the correlated signal from the background signal that appropriately handles complex properties of typical avalanche photodiode (APD) detectors. Also discussed are measurements of relevant APD properties, including count-rate-dependent afterpulsing, delayed (by up to 10 ns) electronic detections and deadtime effects. We show that understanding of these is  essential to perform an accurate calibration.
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By N. Brimhall, J. C. Painter, M. Turner, S. V. Voronov, R. S. Turley, M. Ware, and J. Peatross
Abstract: We report on the development of a polarimeter for characterizing reflective surfaces throughout the extreme ultraviolet (EUV). The instrument relies on laser high-order harmonics generated in helium, neon, or argon gas. The 800 nm laser generates a discrete comb of odd harmonics up to order 100 (wavelengths from 8-62 nm). The flux of EUV light is a couple orders of magnitude less than a synchrotron source but 30,000 times greater than a plasma source currently in operation at BYU. The polarimeter determines the reflectance from surfaces as a function of incident angle, linear light polarization orientation, and wavelength. The instrument uses a wave plate in the laser beam to control the orientation of the harmonic polarization (linear, same as laser). After reflecting from the sample, the harmonic beams are dispersed by a grating and focused onto a micro-channel plate coupled to a phosphor screen. We have demonstrated the feasibility of this project with a simple prototype instrument, which measured the reflectance of samples from 30 nm to 62 nm. The prototype demonstrated that sensitivity is sufficient for measuring reflectances as low as 0.5% for both s- and p-polarized light. The full instrument employs extensive scanning mobility as opposed to the fixed angle and fixed wavelength range of our earlier prototype. An advantage of employing harmonics as a source for EUV polarimetry is that a wide range of wavelengths can be measured simultaneously. This project represents an authentic 'work-horse' application for high-order harmonics, as opposed to merely demonstrating proof of concept.
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By M. Ware (et al.)
Abstract: We investigate the coupling efficiency of parametric downconversion light (PDC) into single and multimode optical fibers as a function of the pump beam diameter, crystal length, and walk-off. We outline two different theoretical models for the preparation and collection of either single-mode or multimode PDC light (defined by, for instance, multimode fibers or apertures). Moreover, we define the mode-matching collection efficiency, important for realizing a single-photon source based on PDC output into a well-defined single mode. We also define a multimode collection efficiency that is useful for single-photon detector calibration applications.