Optomechanical engineering is concerned with maintaining the shape and position of optical components in a variety of environments. Although optomechanics is cen tral to the performance of any optical system, recognition of optomechanics as a separate discipline of optical engineering is relatively recent. Conventional optomechanical methods are no longer adequate to meet the requirements of modern optical systems. This special issue of Optical Engineering is concerned with optomechanical instrument design.

This paper describes three unique metal matrix composite (MMC) material systems that have been developed for use in dimensionally stable platforms, precision mechanical systems, and lightweight reflective optics. These engineered materials, consisting of aluminum alloys reinforced with fine particles of silicon carbide, offer distinctive performance advantages over conventional metals, including greater specific stiffness, higher strength, and better resistance to compressive microcreep. Weighing about the same as aluminum, certain grades of these MMC materials are isotropic and have excellent thermal conductivity, and they can be tailored to match the coefficients of thermal expansion of other materials, including beryllium, stainless steel, and electroless nickel. Such flexibilities in establishing material properties and characteristics present new opportunities to the designer in producing weight-critical, precision hardware. Practical applications of MMC materials in advanced guidance equipment and lightweight optical assemblies are presented and discussed.

The use of layered synthetic microstructures (LSMs) in a diagnostic instrument for focusing x rays from advanced magnetic fusion energy plasmas has been proposed. This paper describes a single-channel prototype of an eventual 20-channel instrument. LSMs are deposited on eight silicon wafer substrates, which provide bendable x-ray mirrors. Each mirror is bent in a four-bar device, and each is subsequently aligned to approximate an off-axis portion of a paraboloid at whose focus is placed a silicon surface barrier detector. The x-ray flux-collecting function of a single channel, together with the low resolution characteristics of the LSM passband and the plasma source geometry, allows for an easily obtained silicon wafer surface figure accuracy. This paper also describes the bending of the LSM mirrors and the installation and alignment of the prototype.

A high precision controller used to accurately drive low inertia galvanometer scanners is presented. Drift errors introduced by the galvanometer position sensor and its electronic driving circuit are compensated using two synchronization photodiodes or phototransistors. The effect of the temperature is analyzed, and comparisons are made with the conventional method of using an analog-to-digital converter to read the signal directly from the position sensor. Absolute accuracy of 10-5 is measured for a change of 10°C. This accuracy is limited to 10-2 when the galvanometer position sensor is used directly. Nonlinearity variations are negligible.

A method has been developed to fit Zernike polynomials to surface deformations computed during finite-element structural analysis. This procedure uses a preprocessor to the finite-element code and allows the polynomial fit to be calculated during both static and dynamic computations.

An active optics system has been built and tested on a prototype 1.8 m lightweight borosilicate glass mirror. Tests of the system have been conducted in two different modes: the system has been used to compensate measured optical surface distortions, and it has been used to correct thermal distortion predicted by computer modeling based on measured mirror temperatures. Both modes were consistently able to reduce rms figure errors on the mirror surface. Test results show that distortions corresponding to astigmatism, coma, spherical aberration, trefoil, and quatrefoil can be effectively countered.

Cathode-ray tubes (CRTs) have many applications in the clinical evaluation of visual functions. They have been used to test visual acuity, contrast sensitivity, visual fields, and early development of vision in preverbal children. Because CRTs provide considerable flexibility for the definition of spatial and temporal components of the stimulus, their use provides an attractive solution to many visual stimulation problems. However, there are some limitations due to the scanning of the picture frame by the electron beam and also to the electron-photon conversion process. The spatial, photometric, spectral, and temporal characteristics of a specifically designed monochromatic television system are evaluated with reference to the physiological requirements of visual tests.

An optical nonsymmetrical imaging system composed of two anamorphic spectrum analyzers in cascade is implemented. This system can provide an undistorted final image in spite of the geometrical distortion effects in the intermediate Fourier plane. The introduction of chromatic sector filters in this plane provides a real-time technique to pseudocolor encode the spatial frequency information of a black-and-white transparency. In this way, greater discrimination is achieved in the angular orientation of object details that generate the same spatial frequencies. Experimental pseudocolored images, obtained with a symmetrical system and a nonsymmetrical system, of a black-and-white transparency are shown.

A noncontacting electro-optical probe is presented that is capable of monitoring the surface height of a sample in ranges of interest for mechanical tooling machines. The surface microtopography is reconstructed after scanning. The working principle is based on monotonic longitudinal chromatic aberration of a lens. Characteristics of a designed lens are reported, along with interferometric testing data on a fabricated prototype. Calibration curves of the complete device are given. After interfacing to a personal computer, automatic probing and scanning are implemented. Results on selected samples are presented.

Microzone plates have been fabricated with the aid of a 100- keV electron beam lithography system. The system has been designed for generating structures with lateral dimensions of less than 100 nm. The particular demands on high resolution, high efficiency imaging Fresnel zone plates and the resultant problems concerning lithography and pattern transfer are discussed. We show a step-by-step improvement of fabricated microzone plates with an outermost zone width of 50 nm. A thin titanium intermediate layer is used as a stable mask to generate ion-milled gold absorber rings with very steep walls. The zone plates have been tested by imaging one another in an x-ray microscope and ave been compared to the image obtained with the holographically fabricated MZP3 microzone plate from Gottingen.

Electronic speckle pattern interferometry has been used to measure the vibrations and deformations of objects located far from the optical head. Vibration recordings were made for a total path-length difference of up to 200 m with the object outdoors in bright sunshine. This limit was determined by practical considerations. For deformation recordings, turbulence and mechanical instabilities create a problem, and a more realistic limit is a path-length difference of about 50 m under stable, indoor conditions.

Mercurous halide crystals (Hg2Cl2, Hg2Br2, and Hg2l2) possess unique acousto-optic properties, including very low acoustic velocities and high figures of merit. These properties make mercurous halide Bragg cells desirable for various optical signal processing applications that are not possible with other acousto-optic materials. This paper discusses and compares the crystal properties and optimum operating conditions and identifies the implications for certain signal processing applications. A discussion of device design for both isotropic and anisotropic configurations is also presented.

The Radon transform is applied to optical inspection of a piece part on a dark background. It is demonstrated that the Radon transform of a "test" object in an arbitrary location and orientation can be restored to the same form as the transform of a similar "reference" object. This can be used to measure the amount of translation and rotation of the object or to introduce rotation and translation invariance properties to calculations performed on transform data. Various image features can be calculated utilizing threshold levels and designated centers to maximize detection capabilities for specific applications. In addition it is shown that it is possible to reconstruct a small region of the image without reconstructing the entire image. This can save time when only a small area is of interest. These techniques for processing Radon transform data are presented in a general manner so that they can be easily applied to fields other than inspection.

The aim of this research is to use holographic interferometry to evaluate the frost susceptibility of concrete. Concrete specimens are subjected to subzero temperatures inside a freezing cabinet. A holographic system is implanted astride both the interior and exterior of the cabinet. Problems related to the implementation of such a measurement system are discussed, and ways to overcome them are described. A fringe control capability eliminates the influence of rigid-body movements and controls the fringe density. The developed system enables one to monitor in real time the evolution of the deformation of concrete specimens exposed to freezing cycles. Besides demonstrating the existence of stresses arising from the thermal incompatibility between the components of the concrete, the method provides an accurate measurement of the temperature at which this thermal incompatibility leads to the impairment of the hardened concrete paste. Results computed from the application of a mathematical model are compared with those obtained by holographic interferometry. Close agreement between the numerically computed and the experimentally observed behavior is obtained.

A method is described to characterize multimode fiber-optic devices in terms of differential mode attenuation (DMA), differential mode delay (DMD), and mode coupling. It is important to describe these complex properties with only a few data. This is accomplished by the mode transition matrix method, in which each fiber optic component is characterized by one or more 3X3 matrices. Certain trade-offs between simplicity and precision are unavoidable, but it has already been demonstrated that the matrix method yields results that are precise enough to calculate system responses properly. Here, mode or pulse transition matrices are defined for the DMD characterization of fibers. Measurements have been carried out.

After a year in which United States presidential candidates, supreme court nominees, and television evangelists offered confession after confession, I have begun to feel that by not confessing something, have not fulfilled my duties as Editor of Optical Engineering. As a result, even if it does rule out any future political aspirations I might have, I have decided that I must confess a shameful deed: I allowed myself to be "bought." That's right! In return for certain favors, I authorized the publication of a paper that otherwise might never have scattered any optical radiation to the eyes of the reader.

Content-Addressable Memories, Second Edition-Reviewed by Mohamad H. Hassoun; Optical Thin Films: Users' Handbook-Reviewed by Karl H. Guenther;