Publisher Summary This chapter discusses the effects of atmospheric turbulence in optical astronomy, summarizes the present state of the theory, reviews the experimental checks that have been made, and discusses the implications in the domain of astronomical observations. Diffraction limited resolution has been obtained with large telescopes up to magnitude 13 by means of speckle interferometry. A Michelson interferometer is already working in the visible on a 20 m baseline up to magnitude 4, and many projects are nearing completion. However, such technological progress can be useful only if accurate quantitative measurements prove to be feasible through atmospheric turbulence. In addition, much work remains to be done before achieving a full understanding of atmospheric effects. The relationship between isoplanicity or speckle boiling and the structure of the atmosphere is still not clear.

V The Effects of Atmospheric Turbulence in Optical Astronomy

Optical techniques have great potential for non-destructive and on-line measurements of surface roughness during manufacturing. This paper reviews the state-of-the-art in a number of optical techniques including specular reflectance, total integrated scatter, diffuseness, angular scattering distributions, speckle, ellipsometry, and interferometry. The distinction is drawn between the more quantitative but slower profiling techniques and less quantitative, parametric techniques, which are faster and hence more useful for high-speed monitoring of surfaces. Overall, no currently available technique combines accuracy and speed and is therefore suitable as an on-line metrological tool for roughness measurement of engineering surfaces. Speckle techniques hold perhaps the greatest potential as accurate, high-speed metrological tools

Optical techniques for on-line measurement of surface topography

Methods for detecting sustained intensity changes in images corrupted by speckle are analyzed. The problem is complicated by the nature of the speckle, which is characterized by a high degree of correlation and (approximately multiplicative) signal dependence. These characteristics make the automated extraction of edges in speckle very difficult for applications requiring the location and identifications of objects (e.g., synthetic aperture radar). In particular, the Laplacian-of-a-Gaussian (LoG) edge detector for this problem is analyzed. While the LoG is found to be effective for detecting meaningful edges, use of the LoG also gives rise to numerous extraneous edges having no physical correlate. To alleviate these effects, a ratio-of-averages edge detector is used in conjunction with the LoG. The combined scheme is found to be much more effective than either of the individual edge detectors. Actual SEASAT synthetic aperture radar (SAR) images are used to demonstrate the effectiveness of each technique. >

On detecting edges in speckle imagery

Optical imaging through complex media has many important applications. Although research progresses have been made to recover optical image through various turbid media, the widespread application of the technology is hampered by the recovery speed, requirement on specific illumination, poor image quality and limited field of view. Here we demonstrate that above-mentioned drawbacks can be essentially overcome. The realization of high speed color imaging through turbid media is successfully carried out by taking into account the media memory effect, the point spread function, the exit pupil of the optical system, and the optimized signal to noise ratio. By retrieving selected speckles with enlarged field of view, high quality image is recovered with a responding speed only determined by the frame rates of the image capturing devices. The immediate application of the technique is expected to register static and dynamic imaging under human skin to recover information with a wearable device.

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High speed color imaging through scattering media with a large field of view.

We propose an optical security method for object authentication using photon-counting encryption implemented with phase encoded QR codes. By combining the full phase double-random-phase encryption with photon-counting imaging method and applying an iterative Huffman coding technique, we are able to encrypt and compress an image containing primary information about the object. This data can then be stored inside of an optically phase encoded QR code for robust read out, decryption, and authentication. The optically encoded QR code is verified by examining the speckle signature of the optical masks using statistical analysis. Optical experimental results are presented to demonstrate the performance of the system. In addition, experiments with a commercial Smartphone to read the optically encoded QR code are presented. To the best of our knowledge, this is the first report on integrating photon-counting security with optically phase encoded QR codes.

Photon-Counting Security Tagging and Verification Using Optically Encoded QR Codes

Publisher Summary This chapter discusses the statistics of speckle patterns. The statistical properties of a speckle pattern depend, in general, on both the coherence of the incident light and the statistics of the scattering surface or medium. In a large number of practical situations normal speckle patterns are produced; the statistics of these speckle patterns are well-established both theoretically and experimentally, and in particular, they do not depend on the detailed scattering properties of the scattering medium. When examining the effects of polychromatic illumination on speckle statistics, it was found that the value of the r.m.s. height variation of a scattering surface strongly influenced the statistical properties of the scattered intensity. In addition, the chapter shows that the general relationship between the scattered intensity and the scattering surface may be very complicated, even for surfaces with a Gaussian distribution of surface heights.

J.C. Dainty

Papers

I The Statistics of Speckle Patterns