Machine-Learning-Inspired Workflow for Camera Calibration.

The performance of modern digital cameras approaches physical limits and enables high-precision measurements in optical metrology and in computer vision. All camera-assisted geometrical measurements are fundamentally limited by the quality of camera calibration. Unfortunately, this procedure is often effectively considered a nuisance: calibration data are collected in a non-systematic way and lack quality specifications; imaging models are selected in an ad hoc fashion without proper justification; and calibration results are evaluated, interpreted, and reported inconsistently.

A retrospective descriptive analysis of non-physician-performed prehospital endotracheal intubation practices and performance in South Africa.

Introduction: Prehospital advanced airway management, including endotracheal intubation (ETI), is one of the most commonly performed advanced life support skills. In South Africa, prehospital ETI is performed by non-physician prehospital providers. This practice has recently come under scrutiny due to lower first pass (FPS) and overall success rates, a high incidence of adverse events (AEs), and limited evidence regarding the impact of ETI on mortality.

Invited review article: measurement uncertainty of linear phase-stepping algorithms.

Phase retrieval techniques are widely used in optics, imaging and electronics. Originating in signal theory, they were introduced to interferometry around 1970. Over the years, many robust phase-stepping techniques have been developed that minimize specific experimental influence quantities such as phase step errors or higher harmonic components of the signal.

Suppression of fundamental-frequency phase errors in phase-shifting interferometry.

I develop and test several new phase-shifting formulas for a Fizeau interferometer, using a spherical cavity of high NA. The associated phase-shift miscalibrations provide a useful range for testing phase-shift error compensation experimentally. After removing the "double-frequency" cyclic phase variation from the error-fringe pattern by well-known methods, the residual phase oscillations occur mainly at 1 and 3 times the fringe frequency.

Null test of an off-axis parabolic mirror. II. Configuration with planar reference wave and spherical return surface.

This paper complements our previous study on testing a 25.4 mm diameter diamond-turned 90 masculine off-axis commercial-quality parabolic mirror with a spherical test wave in a phase-shifting Fizeau interferometer (Opt. Express 17, 3196-3210 (2009).

Null test of an off-axis parabolic mirror. I. Configuration with spherical reference wave and flat return surface.

We demonstrate the precise figure measurement of a one-inch (25.4 mm) diamond-turned 90 masculine off-axis commercial-quality parabolic mirror. The test is carried out with a phase-shifting Fizeau interferometer fitted with a spherical reference surface, auxiliary components and a flat return mirror.

Rapid and reliable reference sphere calibration for Fizeau interferometry.

I describe and demonstrate a rapid and simple technique for calibrating spherical reference surfaces in Fizeau interferometry. A flat mirror at the focus of the test wavefront and a partial occlusion of the test beam enable a double-pass measurement of one half of the surface against the other, which gives an error map for half the aperture. Subsequent rotations of the beam stop and stitching together of several measurements yields the full-aperture calibration file.

A deterministic optical figure correction technique that preserves precision-polished surface quality.

A deterministic surface correction technique has been used to improve the surface figure of two fused silica optical flats over a diameter of 60 mm with no measurable degradation in their surface quality at spatial frequencies of View Article and Find Full Text PDF

Tunable phase-extraction formulae for simultaneous shape measurement of multiple surfaces with wavelength-shifting interferometry.

The interferometric surface measurement of single or stacked parallel plates presents considerable technical difficulties due to multiple-beam interference. To apply phase-shifting methods, it is necessary to use a pathlength-dependent technique such as wavelength scanning, which separates interference signals from various surfaces in frequency space. The detection window for frequency analysis has to be optimized for maximum tolerance against frequency detuning due to material dispersion and scanning nonlinearities, as well as for suppression of noise from other frequencies.

Simultaneous measurement of surface shape and variation in optical thickness of a transparent parallel plate in wavelength-scanning Fizeau interferometer.

Wavelength-scanning interferometry permits the simultaneous measurement of variations in surface shape and optical thickness of a nearly parallel plate. Interference signals from both surfaces of the test plate can be separated in frequency space; however, these frequencies are shifted from the expected frequency by the refractive-index dispersion of the test plate and any nonlinearity that is due to wavelength scanning. Conventional Fourier analysis is sensitive to this detuning of the signal frequency and suffers from multiple-beam interference noise.