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Uncertainty Calculation for Spectral-Responsivity Measurements
No full textThis paper discusses a procedure for measuring the absolute spectral responsivity of optical-fiber power meters and computation of the calibration uncertainty. The procedure reconciles measurement results associated with a monochromator-based measurement system with those obtained with laser sources coupled with optical fiber. Relative expanded uncertainties based on the methods from the Guide to the Expression of Uncertainty in Measurement and from Supplement 1 to the Guide to the Expression of Uncertainty in Measurement-Propagation of Distributions using a Monte Carlo Method are derived and compared. An example is used to illustrate the procedures and calculation of uncertainties
Pass-Fail Testing: Statistical Requirements and Interpretations
No full textPerformance standards for detector systems often include requirements for probability of detection and probability of false alarm at a specified level of statistical confidence. This paper reviews the accepted definitions of confidence level and of critical value. It describes the testing requirements for establishing either of these probabilities at a desired confidence level. These requirements are computable in terms of functions that are readily avail-able in statistical software packages and general spreadsheet applications. The statistical interpretations of the critical values are discussed. A table is included for illustration, and a plot is presented showing the minimum required numbers of pass-fail tests. The results given here are applicable to one-sided testing of any system with performance characteristics conforming to a binomial distribution
(Transcript) Oral history interview of Richard Fields, June 29, 2009 / with Sam Lowe, Jack Rush, Jack Coriell, David Lide, and Hans Oser.
No full textOral history interview of Dr. Richard Fields, formerly with the Metallurgy Division in the Materials Science and Engineering Laboratory (MSEL), National Bureau of Standards (NBS). Dr. Fields first joined NBS as a post doctoral fellow
Pyroelectric Transfer Standard for UV to IR
No full textNIST has one of the most advanced facilities in the world for the calibration of optical sensors, such as those used on satellites for predicting weather and climate, in space telescopes for probing the cosmos, on marine buoys for assessing environmental health, and in a multitude of other applications. The highest level transfer standard for the NIST detector calibration facilities is the Si optical trap-detector calibrated against the primary standard cryogenic radiometer. The limited wavelength range of the Si trap-detector is expanded to the ultraviolet (UV) and the infrared (IR) ranges using the hybrid pyroelectric detectors developed by Gentec EO USA with NIST cooperation. Here, a thin LiTaO3 pyroelectric crystal is coated with a heat absorbing organic-black paint. Earlier, pyroelectric detectors did not have high enough responsivities to use them at the output of regular monochromators. These newly developed transfer standards extended the power responsivity scale from the Si wavelength range for the UV to IR ranges, from 250 nm to 30 micrometers. They can be used at the output of monochromators (widely available even in small laboratories) where the output signal (radiant power) level is low. The prototype was also used as a first-time pyroelectric irradiance meter for the UV to near IR range with 0.25 % relative standard uncertainty. It measured the broadband (integrated) irradiance from LEDs fast and accurate. This inexpensive pyroelectric radiometer is commercially available. Detector, base with On/Off switch, power cube, power cord, and gray plastic and foam case. Material is metal.[H] __[W] __[D] __[Diam] 50 cm __[L] 54.9275 c
Piece of the eyebar that failed and initiated the collapse of the Point Pleasant Bridge (Silver Bridge) on Dec. 15, 1967
No full textA piece of the eyebar that failed and initiated the collapse of the Point Pleasant Bridge (Silver Bridge) on Dec. 15, 1967. This eyebar is part of a display in the National Institute of Standards and Technology (NIST) Museum in Gaithersburg, MD. NIST, (then called the National Bureau of Standards or NBS) was part of the investigation into the cause of the bridge collapse
Model of collapsed Point Pleasant Bridge (Silver Bridge) over the Ohio River
No full textModel of the Point Place Bridge (Silver Bridge) that collapsed into the Ohio River on Dec. 15, 1967. The bridge connected Point Pleasant, West Virginia, and Gallipolis, Ohio. This model is part of a display in the National Institute of Standards and Technology Museum in Gaithersburg, MD. The National Bureau of Standards was part of the investigation into the cause of the bridge collapse
A piece of the eyebar that failed and initiated the collapse of the Point Pleasant Bridge (Silver Bridge) on Dec. 15, 1967
No full textA piece of the eyebar that failed and initiated the collapse of the Point Pleasant Bridge (Silver Bridge) on Dec. 15, 1967. This eyebar is part of a display in the National Institute of Standards and Technology (NIST) Museum in Gaithersburg, MD. NIST, (then called the National Bureau of Standards or NBS) was part of the investigation into the cause of the bridge collapse
Implementation of Two-Dimensional Polycrystalline Grains in Object Oriented Micromagnetic Framework
No full textIn response to the growing need for a more accurate micromagnetic model to understand switching phenomenon in nanoscale magnets, we developed the capability to simulate two-dimensional polycrystalline grains using the Object Oriented Micromagnetic Framework (OOMMF). This addition allows users full flexibility in determining the magnetocrystalline anisotropy and axe in each grain as well as the inter- and intragranular exchange coupling strength
Measurement of Absorption and Scattering With an Integrating Sphere Detector: Application to Microalgae
No full textA spectrometer with an integrating sphere (IS) detector was used to measure the absorbance due to scattering and absorption. Analysis of the measurement process showed that two measurements of the absorbance, one with the cuvette placed in the normal spectrometer position, and the second with the cuvette placed next to the entrance aperture of the IS detector, provide enough information to separate the contributions from scattering and molecular absorption. Measurements were carried out with mixtures of microsphere and chromophore solutions. Two cases were examined: microspheres suspended in an aqueous fluorescein solution, and microspheres suspended in an aqueous holmium oxide solution. In both cases, the proposed measurement model gave results which were in good agreement with the expected response. Measurements on microalgae suspensions yielded a molecular absorption contribution and a scattering contribution. The scattering contribution had significant spectral structure which was inversely related to the molecular absorption contribution. The absorption and scattering contributions may provide independent information on the status of chlorophyll molecules and the structure of chloroplasts in microalgae
Issues in Optical Diffraction Theory
No full textThis paper focuses on unresolved or poorly documented issues pertaining to Fresnels scalar diffraction theory and its modifications. In Sec. 2 it is pointed out that all thermal sources used in practice are finite in size and errors can result from insufficient coherence of the optical field. A quarter-wave criterion is applied to show how such errors can be avoided by placing the source at a large distance from the aperture plane, and it is found that in many cases it may be necessary to use collimated light as on the source side of a Fraunhofer experiment. If these precautions are not taken the theory of partial coherence may have to be used for the computations. In Sec. 3 it is recalled that for near-zone computations the Kirchhoff or Rayleigh-Sommerfeld integrals are applicable, but fail to correctly describe the energy flux cross the aperture plane because they are not continuously differentiable with respect to the assumed geometrical field on the source side. This is remedied by formulating an improved theory in which the field on either side of a semi-reflecting screen is expressed as the superposition of mutually incoherent components which propagate in the opposite directions of the incident and reflected light. These components are defined as linear combinations of the Rayleigh-Sommerfeld integrals, so that they are rigorous solutions of the wave equation as well as continuously differentiable in the aperture plane. Algorithms for using the new theory for computing the diffraction patterns of circular apertures and slits at arbitrary distances z from either side of the aperture (down to z = 0.0003? ) are presented, and numerical examples of the results are given. These results show that the incident geometrical field is modulated by diffraction before it reaches the aperture plane while the reflected field is spilled into the dark space. At distances from the aperture which are large compared to the wavelength ? these field expressions are reduced to the usual ones specified by Fresnels theory. In the specific case of a diffracting half plane the numerical results obtained were practically the same as those given by Sommerfelds rigorous theory. The modified theory developed in this paper is based on the explicit assumption that the scalar theory of light cannot explain plolarization effects. This premise is justified in Sec. 4, where it is shown that previous attempts to do so have produced dubious results