Imaging through turbulence with a quadrature-phase optical interferometer

We present an improved technique for imaging through turbulence at visible wavelengths using a rotation shearing pupil-plane interferometer, intended for astronomical and terrestrial imaging applications. While previous astronomical rotation shearing interferometers have made only visibility modulus measurements, this interferometer makes four simultaneous measurements on each interferometric baseline, with phase differences of π/2 between each measurement, allowing complex visibility measurements (modulus and phase) across the entire input pupil in a single exposure. This technique offers excellent wavefront resolution, allowing operation at visible wavelengths on large apertures, is potentially immune to amplitude fluctuations (scintillation), and may offer superior calibration capabilities to other imaging techniques. The interferometer has been tested in the laboratory under weakly aberrating conditions and at Palomar Observatory under ordinary astronomical observing conditions. This research is based partly on observations obtained at the Hale Telescope

The 2D Continuous Wavelet Transform: Applications in Fringe Pattern Processing for Optical Measurement Techniques

Optical metrology and interferometry are widely known disciplines that study and develop techniques to measure physical quantities such as dimensions, force, temperature, stress, etc. A key part of these disciplines is the processing of interferograms, also called fringe patterns. Owing that this kind of images contains the information of interest in a codified form, processing them is of main relevance and has been a widely studied topic for many years. Several mathematical tools have been used to analyze fringe patterns, from the classic Fourier analysis to regularization methods. Some methods based on wavelet theory have been proposed for this purpose in the last years and have evidenced virtues to consider them as a good alternative for fringe pattern analysis. In this chapter, we resume the theoretical basis of fringe pattern image formation and processing, and some of the most relevant applications of the 2D continuous wavelet transform (CWT) in fringe pattern analysis

Vortex Sheet Simulations of 3D Flows Using an Adaptive Triangular Panel/Particle Method.

In this thesis we present an accurate and efficient algorithm for computing ideal flows using vortex sheets. A vortex sheet is a mathematical model simulating slightly viscous flow in which the vorticity is concentrated on a surface and the viscous effects are small. The sheet surface is represented by a set of triangular panels and each panel contains a set of active and passive Lagrangian particles. The active particles carry vorticity and the passive particles are used for panel subdivision and particle insertion. The method computes the vorticity carried by those particles, and then the induced velocities are computed with a tree-code. As the sheet surface evolves, stretching and twisting occur, hence refinement is needed to maintain resolution. The quadrature and the refinement procedure are local in the sense that they only use information within each panel. The purpose of implementing the locality is to avoid taking derivatives of the flow map, which is difficult because the derivatives grow in amplitude as time progresses. Computations of homogeneous flow, in which vorticity is conserved, are presented. We also present results for slightly stratified flow, in which vorticity is generated baroclinically on the sheet.Ph.D.MathematicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/55669/2/hualongf_1.pd

Roadmap on optical security

Postprint (author's final draft