Adrian Korpel

Image processing for extended depth of field

Improvement in the depth of field is demonstrated by properly processing a succession of image samples. Due to the limited depth of field each image sample has in-focus as well as out-of-focus segments. By setting criteria for selecting the in-focus segments, an improved composite image is formed. Three algorithms for implementing this construction are discussed.

Simplified diffraction theory of the video disk

A simplified model is presented to describe the process of optically reading out a video disk. Although limited in versatility and accuracy, the model has the distinct advantage of not requiring computer solutions and of providing a direct physical insight into the diffraction mechanism of video disk readout. The model is semiquantitative in that predictions are in reasonable numerical agreement with more detailed methods of analysis and with experiments.

Improved space-marching algorithm for strong acousto-optic interaction of arbitrary fields

We present a modification of the beam-propagation algorithm that avoids computer-intensive processing of the sound carrier and instead deals with the slowly varying complex sound profile only. Our three test cases of Gaussian beams with different waists, strongly interacting with a two-dimensional sound column, show excellent agreement with the analytical treatment and with physical experiments performed in our laboratory.

Monte Carlo simulation of the Feynman diagram approach to strong acousto-optic interaction

In previous papers it has been shown that acousto-optic interaction of arbitrary light and sound fields is solvable by means of Feynman diagrams and path integrals. In this paper we use a quantum-mechanical interpretation of these path integrals, based on probability-amplitude densities, for Monte Carlo simulations on a computer. This simulation is applied to a rectangular sound field (moving grating). Results agree with the well-known solutions for Raman–Nath, Bragg, and near-Bragg diffraction.

Beam profiling by vibrating knife edge: Implications for near‐field optical scanning microscopy

We show theoretically and experimentally that beam profiling with a vibrating knife exhibits spatial resolution equal to the knife‐edge excursion. We discuss the implications of this for near‐field optical scanning microscopy, propose an extension of the method to two dimensions, and calculate impulse response, step response, and spatial frequency response.

Matrix formalism for the analysis of acoustooptic beam steering.

A two-order strong interaction matrix formalism is presented for analyzing acoustooptic beam-steering devices operated in the Bragg regime. Matrix solutions are compared with numerical solutions of the coupled differential equations, using ten orders. At the low frequency edge of the Bragg region (Qoverall ≃ 2π) the worst-case discrepancy is ∼1 dB (20%). The accuracy, however, improves rapidly with frequency and transducer length so that, in most cases of practical interest, the matrix method is an acceptable and simple analytic alternative to the numerical solution of the system of coupled differential equations.

Acoustooptic analysis of high frequency wideband sound field schlieren imaging.

Schlieren imaging of acoustic waves has been used routinely for at least half a century. The nature of the image has conventionally been analyzed by various ray tracing techniques or wavefront corrugation calculations. These are restricted to low sound frequencies or thin sound fields. We present a novel method, based on acoustooptic plane wave interaction theory, that not only is applicable to high frequencies but reveals some unexpected features of schlieren imaging.

Two-dimensional operation of a scanning optical microscope by vibrating knife-edge tomography

We analyze and demonstrate a scanning optical imaging system that uses a vibrating knife edge to collect sets of tomographic projection data of two-dimensional objects. Special concerns arising from nonuniform illumination and offset projection data are covered. A tomographic filtered backprojection algorithm is implemented to reconstruct an image from collected projections. Implications for near-field scanning optical microscopy and x-ray microscopy are discussed.

Comparison of phased-array Bragg cells operating in the second order

Three phased-array techniques for acoustooptic generation of light in the more frequency sensitive second order are discussed and compared numerically. A design formalism is developed that may be used on any cascaded configuration of phased arrays. To evaluate the three techniques discussed a broadly applicable strong interaction multiorder numerical method is also introduced.

Gabor: frequency, time, and memory

Dennis Gabor is well-known as the inventor of holography. Less well-known, perhaps, are his contributions to other areas. Yet they are important and, like holography, characteristic of his foresight. In the field of communications, Gabor investigated the classic dichotomy of time and frequency. Guided by analogies to quantum mechanics, he postulated a set of elementary signals and made brilliant use of time-frequency diagrams to analyze communication systems. Applying his theories to acoustics, he researched the mechanism of hearing, defining acoustical quanta in the process and inventing early prototype frequency compressors and expanders. In a completely different field, Gabor, inspired by some early work of Longuet-Higgins on models for holographic temporal recall in the brain, suggested novel approaches which contributed significantly to the understanding of associative memories. In this paper we describe Gabors pioneering work in these areas and trace the subsequent development by himself and others.