W. T. Welford

Bio: W. T. Welford is an academic researcher. The author has contributed to research in topics: Gaussian optics & Geometrical optics. The author has an hindex of 4, co-authored 4 publications receiving 580 citations.

Aberrations of optical systems

Abstract: Optical systems and ideal optical images. Geometrical optics. Gaussian optics. Finite raytracing. Finite raytracing through non-symmetrical systems. Optical invariants. Monochromatic aberrations. Calculation of the Seidel aberrations. Finite aberration formulae. Chromatic aberration. Primary aberrations of unsymmetrical systems and of holographic optical elements. Thin lens aberrations. Optical tolerances.

The Optics of Nonimaging Concentrators: Light and Solar Energy

Abstract: The optical principles for designing nonimaging concentrator are described in detail. Topics include concentrators and their uses; some basic ideas in geometrical optics; some designs of image-forming concentrators; nonimaging concentrators: the compound parabolic concentrator; developments and modifications of the basic compound parabolic concentrator; development of the compound parabolic concentrator for nonplane absorbers; shape tolerances for concentrators; applications to solar energy concentration; and applications of nonimaging concentrators to purposes other than solar energy collection. The appendices include derivation and explanation of the Etendue invariant, including the dynamical analogy: derivation of the skew invariant; the impossibility of designing a perfect imaging system or nonimaging concentrator with axial symmetry; the Luneburg lens; the geometry of the basic compound parabolic concentrator; the THETA/sub 1//THETA/sub 2/ concentrator; the concentrator design for skew rays; the truncated compound parabolic concentrator; and the differential equation for the 2D concentrator profile with nonplane absorber. (WHK)

Optical Calculations and Optical Instruments, an Introduction

Abstract: The physical principles underlying the design of optical instruments are very few in number and yet the process of design has developed to a high level of sophistication and precision. The reason for this may be seen by comparing optical design with other disciplines of apphed physics, e.g. electronic circuit design or the design of pressure vessels. In all cases there is a first order or Unear theory which may be used to obtain a more or less crude approximation to the final design; in circuit design the next stage would usually be the experimental adjustment or trimming of the actual circuit elements, partly to allow for the approximations in the design and partly to allow for manufacturing tolerances on the components; a pressure vessel would usually have such large factors of safety that no further refinement would be needed; but in the optical case the results from the linear theory, the so-called paraxial or Gaussian optics, must then be further refined by taking account of aberrations and finally by exact raytracing before the design is constructed. The Gaussian theory is represented by the linear terms in a power series in several variables which represents the behaviour of the optical system and the aberrations are higher terms in this series; the raytracing process yields the sum of the series for chosen values of the variables. In some physical disciplines there is no equivalent of exact raytracing and in others such a process would be pointless because of manufacturing tolerances on components, but it is possible to make optical systems with great precision and so an elaborate process of optical design can be justified.

Monochromatic aberrations of the human eye in a large population.

Abstract: From both a fundamental and a clinical point of view, it is necessary to know the distribution of the eye's aberrations in the normal population and to be able to describe them as efficiently as possible. We used a modified Hartmann-Shack wave-front sensor to measure the monochromatic wave aberration of both eyes for 109 normal human subjects across a 5.7-mm pupil. We analyzed the distribution of the eye's aberrations in the population and found that most Zernike modes are relatively uncorrelated with each other across the population. A principal components analysis was applied to our wave-aberration measurements with the resulting principal components providing only a slightly more compact description of the population data than Zernike modes. This indicates that Zernike modes are efficient basis functions for describing the eye's wave aberration. Even though there appears to be a random variation in the eye's aberrations from subject to subject, many aberrations in the left eye were found to be significantly correlated with their counterparts in the right eye.

Basic Wavefront Aberration Theory for Optical Metrology

Abstract: VIII. IX. X. XI. XII. Sign Conventions Aberration-Free Image Spherical Wavefront, Defocus, and Lateral Shift Angular, Transverse, and Longitudinal Aberration Seidel Aberrations A. Spherical Aberration B. Coma C. Astigmatism D. Field Curvature E. Distortion Zernike Polynomials Relationship between Zernike Polynomials and Third-Order Aberrations Peak-to-Valley and RMS Wavefront Aberration Strehl Ratio Chromatic Aberrations Aberrations Introduced by Plane Parallel Plates Aberrations of Simple Thin Lenses 2 4 9 12 15 18 22 24 26 28 28

Ground-based and Airborne Telescopes III

Abstract: Cooperating Organizations American Astronomical Society (United States) • Netherlands Institute for Radio Astronomy (ASTRON) (Netherlands) • Ball Aerospace & Technologies Corporation (United States) Canadian Astronomical Society (CASCA) (Canada) • European Astronomical Society (Switzerland) • ESO—European Southern Observatory (Germany) • International Astronomical Union • Korea Astronomy and Space Science Institute (KASI) (Republic of Korea) • National Radio Astronomy Observatory • POPSud (France) • TNO (Netherlands)

Three-Dimensional Localization of Single Molecules for Super-Resolution Imaging and Single-Particle Tracking

Abstract: Single-molecule super-resolution fluorescence microscopy and single-particle tracking are two imaging modalities that illuminate the properties of cells and materials on spatial scales down to tens of nanometers or with dynamical information about nanoscale particle motion in the millisecond range, respectively. These methods generally use wide-field microscopes and two-dimensional camera detectors to localize molecules to much higher precision than the diffraction limit. Given the limited total photons available from each single-molecule label, both modalities require careful mathematical analysis and image processing. Much more information can be obtained about the system under study by extending to three-dimensional (3D) single-molecule localization: without this capability, visualization of structures or motions extending in the axial direction can easily be missed or confused, compromising scientific understanding. A variety of methods for obtaining both 3D super-resolution images and 3D tracking inf...

A subpicotesla diamond magnetometer

Abstract: Diamond defect centers are promising solid state magnetometers. Single centers allow for high spatial resolution field imaging but are limited in their magnetic field sensitivity to around 10 nT/Hz^(1/2) at room-temperature. Using defect center ensembles sensitivity can be scaled as N^(1/2) when N is the number of defects. In the present work we use an ensemble of 1e11 defect centers for sensing. By carefully eliminating all noise sources like laser intensity fluctuations, microwave amplitude and phase noise we achieve a photon shot noise limited field sensitivity of 0.9 pT/Hz^(1/2) at room-temperature with an effective sensor volume of 8.5e-4 mm^3. The smallest field we measured with our device is 100 fT. While this denotes the best diamond magnetometer sensitivity so far, further improvements using decoupling sequences and material optimization could lead to fT/Hz^(1/2) sensitivity.