In my editorial in the November 1987 issue of Optical Engineering, II invited reader response to Joe Geary's recommendation that we accept "idea-type" papers for publication in the journal. An "idea-type" paper is, presumably, one that simply puts forth ideas without including any results or substantiated conclusions. I received a response from Bud VanderLugt, who is opposed to this idea, and I will attempt to paraphrase his remarks in the following paragraphs.

Fourier Optics: An Introduction, Second edition-reviewed by Michael Hendry; Opto-Electronic Imaging-Reviewed by Ronald P. Slegtenhorst; The Complete Book of Holograms-How They Work and How to Make Them-Reviewed by H. John Caulfield

Many readers of Optical Engineering may find the word photomechanics confusing. It is a term coined by Dr. A. J. Durelli almost 30 years ago (indeed he has a book with this title: introduction to Photomechanics, by A. j. Durelli and W. F. Riley, Prentice-Hall Inc., 1965) to describe a discipline wherein the practitioners use optical methods such as photoelasticity to perform stress analysis of structures under Ilioad. Since then, the meaning of photomechanics has Ibroaderned to include the study of all mechanics problems (e.g., deformation of solids and flow of fluids) using optical techniques.

A new method of automatic fringe analysis for particle image velocimetry (PIV) data reduction is presented. The technique is based on calculating the positions of coincident peaks in the cross-correlation of pairs of separated parallel lines of data in the fringe pattern. Preliminary results show that an efficient automatic data reduction system can be realized using this approach.

The accurate determination of the velocity vector from a particle image velocimetry (PIV) transparency depends on the number of image pairs that have been recorded in the region under examination. If one particle pair is present, there is an ambiguity of rad in direction. Two particle pairs give four ambiguous velocity vectors. This paper describes a new approach in PIV that resolves the ambiguity problem and potentially increases the dynamic range of the technique.

We describe a point diffraction interferometer (PDI) for use in connection with stressed fluids. Since the wavefront distortions are conspicuous, the transmitted field breaks down into a speckle distribution. A speckle chaser has been devised so that a bright speckle is always kept on top of the PDI pinhole. Adequate power for the selfgenerated reference beam is thus available, and fringe visibility remains quite satisfactory even for large optical distortions.

The theoretical basis of holospeckle interferometry is laid out. Several schemes for this new technique are presented, along with demonstrations of its varinus annlinatinns

Objective speckle from a stick-on foil is a new approach to applying the objective white light speckle method to in-plane displacement measurements. By a relatively easy technique a thin aluminum foil is mounted onto the specimen surface and a random grating is scratched onto it, yielding high reflectance and fine optical details. After double exposure by a direct recording system without using a lens, the resulting holographic film possesses a broad spatial spectrum and displacement information. Full-field contour maps of equal displacement can be obtained that are of good contrast and high sensitivity and that have a large adjustable measurement range. The method can be applied to practical engineering problems for both plane and developable curved surfaces.

An embedded random speckle technique is used to measure the displacement in the near-crack-tip fields in four-point-bending beams made of transparent materials. Stress intensity factors or strains in the different planes are generated from the displacement measurements. The results are compared with the existing theoretical and numerical solutions.

Basic principles and advances of the laser speckle strain gauge are described. The gauge optoelectronically detects speckle displacements caused by deformation of a diffuse surface and separates strain by means of a differential optical system. The method is noncontacting and automatic. Several problems for practical application of the gauge are presented, together with proposals for solving them.

The paper presents some developments in the application techniques of double-exposure moire interferometry, with the aims of simplifying the technique and overcoming some of its current drawbacks. The main proposed development is the substitution of the classic interferometric setup, which records a high density grating on the specimen, by a high density, highly efficient double (crossed) holographic grating, clamped onto the object just in front of it. The following main advantages are recognized: Since the holographic grating is clamped onto the object and follows its rigid motion, the corresponding effect on the fringes Fs minimized. The coherence length requirements for the laser are minimized to a fraction of the distance from the grating to the object. An argon laser without etalon can be used, an obvious advantage given the low sensitivity of the photosensitive coatings. The specimen needs to be (doubly) exposed only once to obtain the two orthogonal sets of displacement fringes, thanks to the use of a crossed grating. Thus, errors due to the low repeatability of the test are avoided. Some applications, including the use of unusual photosensitive coatings and processing procedures, are presented.

In the process of determining the complete state of stress at a general point in a three-dimensional photoelastic model (in a nondestructive or a semidestructive manner), the concept of an optically equivalent model plays an important role. An optically equivalent model is defined by three parameters, which are termed characteristic parameters. This paper first surveys the direct and indirect methods used to determine the characteristic parameters and then presents a new indirect method for determining these parameters. An algorithm has been developed to determine the characteristic parameters unambiguously by the new method. The new method is verified experimentally and results are compared with theoretical characteristic parameters determined using Jones calculus.

A microcomputer-based moire strain gauge with high sensitivity is developed that is capable of measuring strain automatically.

Pulse-shaping experiments in a 100 Am thick CdS etalon have been performed with a pulsed frequency-doubled Nd-YAG laser. The incident laser pulse produces changes in the refractive index, and the CdS etalon is tuned over a few resonances. From these experiments a refractive index change in CdS of An = 0.0035 can be estimated. We also report pulse-shortening experiments with the CdS etalon. Finally, we have investigated the self-refraction of Gaussian laser beams in the CdS sample. We observe self-defocusings, which indicate that the dominant mechanism for the nonlinear refraction is not of thermal origin.

Direct detection free-space optical communication using laser diode transmitters has been proposed for use on NASA's Advanced Communication Test Satellite (ACTS). The investigation reported here examines a prototype laser diode array for this purpose, having a variable spacing between the emitter stripes (VSA). The device was designed to output a moderately powerful beam into a narrower single-lobed radi-ation pattern than that of the (currently) more powerful regular-spacing phase-locked arrays (RSAs). Key parameters were measured to determine whether the VSA would be a good candidate for use in the ACTS system. Measurements showed a superior electrical frequency response, superior impulse response, and a slightly narrower far-field radiation pattern compared with the RSA. However, the limited output power of the VSA realistically precludes its use in a free-space optical communication system even when a polarization beam-combining system is used.

A new method, exclusively applicable to retroreflective objects, is proposed for making rainbow holograms. The object is illuminated with a coherent wave scattered from a diffuse slit. The retroreflected object beam retraces the path of the incident beam, thus producing a slitlike function in the plane of convergence.

In electro-optical detector systems, the noise characteristics of transresistance amplifiers are sensitive to the incremental conductivity of the photovoltaic detector. In this paper we show that the 1/f noise corner frequency contributed to the noise by the amplifier is a function of the bias applied to the detector. The 1/f noise corner frequency of the diode in cooled focal plane arrays is also a function of the reverse bias, but there is an optimum reverse bias that is not 0 V. This fact becomes important when it is necessary to use complementary metal oxide semiconductor amplifiers that have lame 1/f noise corner frequencies.

Effective widths are given to estimate source size and divergence of radiation from undulators. We show the strong variation of these with detuning from the peak and the corresponding values of the photon emittance and optimum beta. At large detuning, the diffraction size increases with increasing angular width, confirming that for a coherent wave, diffraction and depth-of-field broadening are the same thing.

An actuator was built that positions three fiber optic bundles in front of an optical sensor at different times. The design is such that while the sensor views one bundle, it does not see the light from the other two bundles. The device may be described as a linear-displacement, tandem-mounted, solenoid-actuated optical switch. It is the optical equivalent of a single-pole triple-throw electrical switch. Its operation is based upon a three-position linear displacement. The displacement is the result of allowing the termination block of the fiber optic bundles and one pull-type solenoid to be mounted on near-frictionless slider tables. Another solenoid mounted behind the first one displaces these two items so that three positions are possible. Springs return the system to its initial position, predetermined by stop blocks. The solenoids are energized by 120 V ac and controlled by a simple relay circuit that is prompted by a computer.