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

As a result of development of optics during many centuries the concept was formed that a medium can strongly influence on the light propagation, but the light itself cannot have backward influence on the medium. That concept was refuted only with appearing of coherent and high power radiation of lasers, see, e.g., Nobel Lecture by N. Bloembergen in 1981. A new field in physics–nonlinear optics—formed as a result. The main part of laser investigations concerns with nonlinear optical phenomena, nowadays. First of all these phenomena are of extraordinary interest and beauty and provide for new methods of physical investigations. Secondly, the knowledge of laws governing the interaction of a powerful light with a medium is necessary for the correct utilization of laser beams. Finally, a great number of devices of up-to-date laser optics is totally based on utilization of nonlinear optical effects; generation of higher harmonics of light, stimulated scattering of light, optical phase conjugation, self...

Orientational Optical Nonlinearity of Liquid Crystals

An application of the Ts–VI triangle method with enhanced edges determination for evapotranspiration estimation from MODIS data in arid and semi-arid regions: Implementation and validation

This paper concerns binary digital computing systems in which the information-carrying medium consists entirely or primarily of photons. The paper begins with a review of analog, discrete, and binary methods of representing information in a computer, followed by a survey of many techniques for implementing binary combinatorial and sequential logic functions with individual optical devices and arrays of devices. Next is a discussion of communication, interconnection, and input-output problems of digital electronic and optical computers at the gate, chip, and processor level. A particular architecture for implementing general sequential optical logic systems including digital optical processors is described. This architecture avoids some of the interconnection problems of electronic integrated circuits and VLSI systems, and offers the potential of non von Neumann parallel digital processors. Finally, the current limitations and future needs of optical logic devices and digital optical computing systems are outlined.

Digital optical computing

A set of micro-meteorological data collected over a horizontal, uniform terrain (the plain of La Crau, France) in June 1987 is analysed. Conditions were predominantly sunny and arid, while due to the “Mistral” the wind speed could exceed 10 m/s. Verification of several methods to evaluate surface fluxes of heat, momentum and water vapour from the standard deviation of temperature, wind and specific humidity is presented. Also, a similar approach using the structure parameter of temperature is considered. These methods are all based on Monin-Obukhov (M-O) similarity theory. It is found that the standard deviation of temperature, vertical and horizontal wind speed as well as the structure parameter for temperature behave according to M-O similarity. It is shown that the sensible heat flux and friction velocity can be determined from a fast response thermometer and a cup anemometer. Also, it appears that the analytic solution of the set of governing equations as derived by the first author yields good results. M-O theory does not appear to work for the standard deviation of specific humidity. This may be due to the relative importance of large eddies.

A verification of some methods to determine the fluxes of momentum, sensible heat and water vapour using standard deviation and structure parameter of scalar meteorological quantities.

This paper deals with the propagation of coherent light through lens systems; it relates diffraction theory to ray optics. A diffraction integral is derived which relates the electromagnetic fields on the input plane of a lens system to those on its output plane. The kernel of the diffraction integral is written in terms of the elements of the ray matrix that describes the complete lens system; that kernel indicates a connection between ray optics and diffraction theory. It also provides a simple method for writing the diffraction integral for a lens system. The results are limited to the paraxial-ray approximation, but apply to symmetric and asymmetric lens systems. In the case of asymmetric systems, i.e., those containing rotated elliptical or cylindrical lenses, the ray-matrix formalism is extended so as to use a single fourth-order matrix. The diffraction integrals derived are applied to optical spatial filtering, optical-beam waveguides, optical resonators, and holography.

Lens-System Diffraction Integral Written in Terms of Matrix Optics

A semiempirical theory is developed which relates the refractive-index-structure parameter Cn2 in the lowest few tens of meters to the vertical gradients of wind speed and temperature and to a stability parameter. This provides an indirect method of determining Cn2, or its temperature counterpart CT2, and the method is successfully applied to recent data which include directly measured CT2 values. The height dependence of the structure parameter is also determined, and the predicted z−4/3 profile under unstable conditions agrees with recent data in the free atmosphere at heights up to 500 m.

Behavior of the Refractive-Index-Structure Parameter near the Ground*

In this paper, we propose a new method of optically implementing digital logic gates capable of performing all logic operations and give the technique for construction of an array of n-bit parallel adders as a typical application circuit. These gates are implemented using a Hughes liquid crystal light valve operated in the parallel off-state configuration. It is found that all possible functions of two binary variables are realizable with these gates, some as bright-true-logic and some as dark-true-logic. Experimental results will be given using the portions of a single liquid crystal light valve demonstrating the feasibility of AND, NOR, XOR, etc. gate arrays. As an example of implementation of combinatorial circuits, a design for an array of binary adders will also be given.

Optical logic gates using liquid crystal light valve: implementation and application example

This paper is concerned with the application of optics to digital computing. A Hughes liquid crystal light valve is used as an active optical element where a weak light beam can control a strong light beam with either a positive or negative gain characteristic. With this device as the central element the ability to produce bistable states from which different types of flip-flop can be implemented is demonstrated. In this paper, some general comments are first presented on digital computing as applied to optics. This is followed by a discussion of optical implementation of various types of flip-flop. These flip-flops are then used in the design of optical equivalents to a few simple sequential circuits such as shift registers and accumulators. As a typical sequential machine, a schematic layout for an optical binary temporal integrator is presented. Finally, a suggested experimental configuration for an optical master-slave flip-flop array is given.

Stuart A. Collins

Papers

Lens-System Diffraction Integral Written in Terms of Matrix Optics

Behavior of the Refractive-Index-Structure Parameter near the Ground*

Optical logic gates using liquid crystal light valve: implementation and application example

Optical flip-flops and sequential logic circuits using a liquid crystal light valve

Optical Effects of Surface Finish by Ultraprecision Single Point Diamond Machining