The low-latency requirements of a loophole-free Bell test prohibit time-consuming post-processing steps that are often used to improve the statistical quality of a physical random number generator (RNG). Here we demonstrate a postprocessing-free RNG that produces a random bit within 2.4(2) ns of an input trigger. We use the Allan variance as a tool for characterizing non-idealities in the RNG and designing a feedback mechanism to account for and correct long-term drift. The impact of the feedback on the predictability of the output is less than 6.4 × 107 , and results in a system capable of 24 hour operation with output that is statistically indistinguishable from a balanced Bernoulli process.
The National Institute of Standards and Technology (NIST) has maintained scales for reflectance and transmittance over several decades. The scales are primarily intended for regular transmittance, mirrors, and solid surface scattering diffusers. The rapidly growing area of optical medical imaging needs a scale for volume scattering of diffuse materials that are used to mimic the optical properties of tissue. Such materials are used as phantoms to evaluate and validate instruments under development intended for clinical use. To address this need, a double-integrating sphere based instrument has been installed to measure the optical properties of tissue-mimicking phantoms. The basic system and methods have been described in previous papers. An important attribute in establishing a viable calibration service is the estimation of measurement uncertainties. The use of custom models and comparisons with other established scales enabled uncertainty measurements. Here, we describe the continuation of those efforts to advance the understanding of the uncertainties through two independent measurements: the bidirectional reflectance distribution function and the bidirectional transmittance distribution function of a commercially available solid biomedical phantom. A Monte Carlo-based model is used and the resulting optical properties are compared to the values provided by the phantom manufacturer.
We present a general quantum-mechanical formalism to describe photon-pair generation via four-wave mixing in a
Silicon-on-Insulator (SOI) microresonator. We also provide design principles for efficient photon-pair generation
in an SOI microresonator through numerical simulations. Ring-cavity designs are shown to have a much wider
dispersion-compensate frequency range than straight-cavity designs. Such on-chip quantum devices are highly
promising for future integrated quantum information processing.
Recently, extreme ultraviolet interference lithography using a single grating interferometer and a highly coherent synchrotron insertion device source has proven to be an extremely useful technique for producing patterns with feature sizes in the range of 10 nm. The high demand for these nanoscale patterns and the small number of suitable highly coherent extreme ultraviolet sources has created new interest in the cascaded grating interferometer because of its relaxed demands for spatial and temporal coherence. This work extends that of earlier researchers on such systems by providing a compact algebraic analysis of the effects on fringe contrast of source divergence, spectral bandpass, lack of parallelism of the grating rulings, grating period mismatch, defocus, and wavefront curvature. The results are applied to illustrate the feasibility of implementing the interferometer on a small bending magnet synchrotron source, but the analysis should be applicable to typical portable plasma sources as well.
Recently, Levine, Kearsley, and Hagedorn proposed a generalization of generalized Gaussian random Markov field (GGMRF) as developed by Bouman and Sauer. The principal components of the Bouman-Sauer formulation are a quadratic approximation to the log-likelihood assuming a Poisson distribution and a Beer's Law interaction and a prior distribution which penalized deviation of the values in a neighborhood as a user-defined power in the interval (1-2]. The generalization removes the restriction that the transmission function follows Beer's Law, but instead admits any functional form for the transmission-thickness relation, such as those arising in transmission electron microscopy of thick samples. Several illustrative examples are given in this paper.
Samples a few micrometers in total size offer a challenge to both x-ray and electron tomography. X-ray tomography originated imaging the human body with millimeter resolution, but the resolution has been reduced by over 7 orders of magnitude by the use of synchrotron sources and Fresnel zone plates, leading to an achieved resolution of 20 nm in favorable cases. Further progress may require phase retrieval. Electron tomography originated on very thin samples (perhaps 100 nm thick) but recently samples of over 1 micrometer have been studied with conventional instruments. The study of thicker samples requires understanding tomography in the multiple scattering regime.
The discovery of a significant spatial-dispersion-induced birefringence (intrinsic birefringence) in CaF2 at ultraviolet wavelengths has had a major impact on the design of 157 nm lithography systems, requiring complete redesign of the optics to take account of the imaging aberrations resulting from the birefringence and the accompanying index anisotropy. This intrinsic birefringence phenomena results from a symmetry-breaking effect of the finite wave vector of the photon on the symmetry of the light-matter interaction in fluorite-structure cubic crystals. As a follow-up to our original concise report of measurements and theory of the effect in CaF2 and BaF2, we present here a more detailed analysis of the theory, focusing on the symmetry and its consequences. We also provide the full directional dependence of the effect in useful closed forms. We analyze the implications for precision optical design with CaF2 optical elements, and discuss qualitatively the approaches being considered to compensate for it.
Artifacts induced by distortions which sometimes occur in two- dimensional projection images can appear in the resulting tomographic reconstructions. We describe a procedure for analyzing, correcting and removing experimental artifacts, and hence reducing reconstruction artifacts. Two-dimensional and three-dimensional images acquired with scanning transmission x-ray microscopy of a sample containing an integrated circuit interconnect show how these procedures can be successfully applied.
We performed an x-ray nanotomography experiment at the Advanced Photon Source for the purpose of making a 3D image of a sample contain an integrated circuit interconnect. Nine projections of the sample were made over an angular range of 140 degrees using 1573 eV photons and scanning transmission x-ray microscope having a focal spot size of about 150 nm. Reconstructions of experimental and simulated data, using a simultaneous iterative reconstruction technique, show that a sample that is highly opaque along certain lines of sight must be strategically oriented with respect to the rotation axis to minimize the attenuation of photons through the sample and maximize the contrast in each image.
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