J. C. Dainty

Iterative blind deconvolution method and its applications

A simple iterative technique has been developed for blind deconvolution of two convolved functions. The method is described, and a number of results obtained from a computational implementation are presented. Some further possible applications are indicated.

SIMULATION OF A KOLMOGOROV PHASE SCREEN

Abstract Two new methods for modelling Kolmogorov phase fluctuations over a finite aperture are described. The first method relies on the incorporation of subharmonics in order to model accurately the low frequencies of the Kolmogorov spectrum. The second method provides a less accurate, but much faster method for simulating the Kolmogorov spectrum by using a midpoint displacement algorithm used in computer graphics.

Experimental study of enhanced backscattering from one- and two-dimensional random rough surfaces

An experimental study of backscatter enhancement from rough surfaces is presented. The Stokes parameters of the average scattered light from two-dimensional rough surfaces show the presence of an unpolarized component, which lends support to the multiply scattering ray model. Experimental data from one-dimensional rough surfaces are compared with numerical calculation.

A low cost adaptive optics system using a membrane mirror

A low cost adaptive optics system constructed almost entirely of commercially available components is presented. The system uses a 37 actuator membrane mirror and operates at frame rates up to 800Hz using a single processor. Numerical modelling of the membrane mirror is used to optimize parameters of the system. The dynamic performance of the system is investigated in detail using a diffractive wavefront generator based on a ferroelectric spatial light modulator. This is used to produce wavefronts with time-varying aberrations. The ability of the system to correct for Kolmogorov turbulence with different strengths and effective wind speeds is measured experimentally using the wavefront generator.

Knox-Thompson and triple-correlation imaging through atmospheric turbulence

A comparative study is made of the Knox–Thompson and triple-correlation techniques as applied to image restoration. Both photon-noise-degraded imaging and atmospheric-turbulence-degraded imaging are considered. The signal-to-noise ratios of the methods are studied analytically and with the aid of computer simulations. The ability to retain diffraction-limited information on imaging through turbulence is considered in terms of phase-closure relationships. On the basis of this work it is found that the two image-restoration techniques are effectively equivalent.

Sub-100- mu m depth-resolved holographic imaging through scattering media in the near infrared.

We discuss the compromise between depth and transverse spatial resolution for photorefractive holographic imaging through turbid media. Results from an optimized geometry for a 45°-cut rhodium-doped barium titanate photorefractive crystal are presented, demonstrating two-dimensional imaging through turbid media with both sub-100-μm depth and transverse spatial resolution.

Some Statistical Properties of Random Speckle Patterns in Coherent and Partially Coherent Illumination

The power spectrum of the intensity fluctuations in a random speckle pattern is derived in a simplified manner for coherent illumination. The effect of the power spectrum on the measured signal-to-noise ratio is discussed, and some preliminary measurements of the power spectrum are presented. The power spectrum of the intensity fluctuations for partially coherent illumination is derived for the special case of an aberration-free system, using quadratic filter theory.

Estimation of spatial power spectra in speckle interferometry

Calculations of the signal-to-noise ratio (SNR) of estimates of the power spectra of spatially varying random processes, such as stellar speckle patterns, usually include realizations that contain less than two detected photons. It is shown in this paper that if these cases are excluded from the analysis procedure either implicitly or explicitly, then under the usual definition of SNR, the overall SNR of an estimate can increase by up to a factor of N¯−1/2, where N¯≪1 is the average number of detected photons per realization.

DEPTH-RESOLVED HOLOGRAPHIC IMAGING THROUGH SCATTERING MEDIA BY PHOTOREFRACTION

A depth-resolved near-infrared imaging system has been demonstrated for recording three-dimensional images of objects embedded in diffuse media. Time-gated holographic imaging employing rhodium-doped barium titanate as the recording medium is used to acquire whole depth-resolved two-dimensional images in 1 s. Millimeter depth resolution has been achieved with a transverse resolution of ~ 30 microm.

Stellar Speckle Interferometry

Stellar speckle interferometry is a technique for obtaining diffraction-limited resolution of stellar objects despite the presence of the turbulent atmosphere which limits the resolution of conventional long-exposure pictures to approximately one arc second. It was invented by Labeyrie [7.1] and the first results using the 5 m Hale telescope at Mount Palomar were presented in 1972 [7.2]. Speckle interferometry can be regarded as a method of finding the modulus of the degree of coherence in the far field of an incoherent source and is essentially the same as a method suggested independently by Asakura et al. [7.3] for the determination of the spatial coherence of light emitted by laboratory sources. There is also a very close relationship between stellar speckle interferometry and some of the information processing and engineering applications of speckle patterns described in Chapters 5 and 6.