The real-time information processing and manipulation of electromagnetic waves using nonlinear Qptical techniques has resulted in a myriad of new applications in diverse fields such as quantum electronics, image processing, optical computing, adaptive optics, and nonlinear spectroscopy. In this paper, we review and explore the field, provide a historical perspective, analyze several of the nonlinear interactions useful for the generation of phase-conjugate replicas, and conclude with a brief survey of potential applications and suitable nonlinear media.

The transient response of Kerr-like phase conjugators is treated and reviewed. The cases of cw and transient pump waves are considered. A general formalism is derived, with application to specific cases such as pulse reshaping, chirp reversal, and temporal reversal of optical waveforms.

The use of resonantly enhanced four-wave mixing to generate high reflectivity phase-conjugate waves is discussed. A physical understanding of the mechanisms underlying the nonlinear response for a simple two-level system is presented followed by a discussion of the complicating effects of pump absorption, pump depletion, unbalanced pumps, and thermal motion. Modifications of the theory to describe four-level behavior are presented and compared with experiments. The application of nearly degenerate four-wave mixing to narrow-band filtering complicated by the A. C. Stark effect is dis-cussed along with examples of experimental observations.

Semiconductors appear to have excellent potential as materials for phase conjugation via degenerate four-wave mixing (DFWM) because of the large variety of nonlinear optical mechanisms that may be invoked in them. When the optical wavelength is near or above the band gap, mobile particles such as free electrons and holes or free excitons may be created; in such cases, DFWM itself provides a powerful contact-free and nondestructive technique for the study of carrier transport and decay parameters, such as ambipolar diffusion coefficients and recombination times. In this article, we briefly review the various nonlinear mechanisms that may be used for DFWM, as well as the various DFWM and related "transient grating" experiments that have been performed for application to phase conjugation and to carrier dynamics studies.

The physics underlying the technique of degenerate four-wave mixing (DFWM) is presented. Its application to the measurement of energy decay and dephasing rates is considered in the regime of small absorption and coupling coefficients.

The versatility of degenerate four-wave mixing (D4WM) has made possible its application to two major areas of spatial information processing: distortion correction and mathematical operations. The first area can be divided into predetection and postdetection processing. Distortions can be compensated for before the imaging. process by exploiting the phase-conjugating capability of D4WM. Phase-conjugate mirrors (PCM's) may also find use in optical processors designed to remove distortions after the imaging process is complete and the object is no longer available. Examples of linear operations that can be implemented using the nonlinear optics of D4WM are image convolution and correlation. An example of a nonlinear mathematical operation that can be implemented using D4WM is edge detection of two-dimensional images.

Three approaches to active compensated imaging are proposed, in which one or more nonlinear phase conjugators effectively compensate for atmospheric turbulence-induced image degradations. In all cases the imaging system aperture and all auxiliary apparatus are located proximal to the active illumination aperture, in contrast to previously discussed system implementations, and the references which are employed are natural features of the image object.

The use of nonlinear optical techniques for the temporal processing of information encoded as envelopes on electromagnetic fields is discussed. Applications using these all-optical interactions in the areas of signal processing, radar, and communication systems are considered and compared with existing approaches.

This paper assesses the potential for and the key problem areas associated with the wavefront compensation of moderate- to high-power laser amplifier systems via nonlinear optical conjugation techniques. Laser fusion drivers provide the prime example of such compensation schemes.

Wavefront reversal (WFR) via stimulated Brillouin scattering (SBS) is shown to possess the capability to compensate for phase aberrations in laser media and also to temporally compress long laser pulses. Such techniques, which involve passive and lightweight conjugator elements, are believed to be simple and practical.

We review the history and nature of stimulated scattering of optical beams and of the large phase-conjugate component often observed in stimulated backscattering, whether it be of Raman, Brillouin, Rayleigh, or other origin. We review the theory of the magnitude of the phase-conjugate component in stimulated backscattering of waves in a multimode optical guide (the usual experimental configuration) or in free focus. Wide applicability of stimulated backscattering for optical phase conjugation is found.

Theory and experiments are reviewed which suggest that optical-beam phase conjugation by four-wave mixing in a waveguide has the following advantages over four-wave mixing of unguided waves: (1 ) pump power requirements are reduced; (2) the pump beams can contain many transverse modes, both outside and inside the waveguide; (3) pump beam alignment is not critical; (4) the image-wave, being conjugated, can serve simultaneously as its own pump beam; (5) many frequencies can be conjugated simultaneously without intermixing of signals; and (6) frequency- and angle-response characteristics of the conjugator as an optical filter are extended. Frequency depen-dent resonances in the phase-conjugate signal may be employed in spectroscopy of small samples.

Unique properties of transverse and axial modes of phase-conjugate-mirror resonators are discussed and experimental results already published are summarized.

We discuss how novel arrangements of conventional (static/linear) optical elements can compensate for many classes of time-varying phase distortions in optical trains. Precision corner arrays, lens arrays, and K-mirror arrays are all applicable as pseudoconjugation elements in certain classes of problems. In some cases multipassing (four or more passes) of a distorting medium can offer improved performance. Although the compensation is more limited than that available from nonlinear optical phase conjugation (NOPC), problems associated with thresholds, pumps, and frequency translations are eliminated.

A summary of experiments is presented which show how retrodirective arrays have been used to approximate phase conjugation.

Thermographic inspection is an invaluable diagnostic tech-nique for detecting thermal abnormalities indicative of failure mechanisms in current-carrying equipment. No other maintenance procedure can provide such fast and accurate evaluation of the operating condition of electrical apparatus. Infrared line scanners and infrared imagers are both used successfully for thermographic inspection surveys. Each system has certain advantages and disadvantages. The Barnes Thermatrace single-line scanner and the AGA Thermovision 750 imager are compared. Periodic thermographic inspection surveys in commercial and industrial plants substantially reduce the frequency of equipment failures and unscheduled power outages. Proper planning and organization increase the efficiency of a survey and reduce the cost. Several ex-amples illustrate some of the types of failure mechanisms frequently encountered.

The use of laser annealing with a CO2 laser to improve the quality of both Corning 7059 and phosphosilicate glass (PSG) thin-film optical waveguides will be described. Dark-field photomicrographs taken before and after laser annealing imply that both surface and bulk defects are removed by laser annealing. Waveguide attenuation is typically measured to be on the order of 10 dB/cm before laser annealing, while after laser annealing values significantly lower than 0.1 dB/cm have been measured. We shall discuss the integration of a photodetector array and the optical waveguide structure, and the fact that for such a structure less scattering reaches adjacent array elements than when these two structures are not integrated. The dynamic range of the integrated optical signal process of interest would thus be expected to be greater for the integrated configuration.

Through measurements of modulation transfer functions (MTF), the imaging characteristics of three x-ray image intensifiers equipped with dissimilar input face designs coupled with photoflouorographic cameras were evaluated in the clinical environment. The MTF data enabled one to correlate and compare the clinical impressions of these imaging systems in a quantitative manner to evaluate and determine the feasibility of utilizing these imaging systems for different clinical approaches.

This paper reports the technique for determining the thickness profile (i.e., the variation of thickness as a function of radial distance) for a deformable glass mirror whose inner surface must always maintain a spherical shape. The convex mirror produced by the periodic deformation (i.e., from optically flat to maximally spherical deformation of the optical surface at a given sinusoidal frequency) has associated with it a dynamically varying focal spot. The mirror is designed to assume a convex chape which is perfectly spherical over its deformation range, thus providing a varying negative focal point which can be incorporated into an associated optical system making use of the fluctuating focal position. The mirror thickness profile is determined by solving the equation of motion for a variable thickness plate with the constraint that the deformed surface be perfectly spherical when a uniform load is applied to the back surface of the plate. The final result gives the thickness as a function of radius with load, frequency, and physical constants of the plate as parameters. This work has significance in the field of adaptive optics.

Progress in the research devoted to developing x-ray lasers is reviewed as it pertains to one-electron hydrogenic ions created and pumped to inversion in high-density laser-produced plasmas. A simple analysis defines a useful parameter space. Measured gain coefficients for C5+ are in good agreement with modeling for electron-capture pumping. Photon pumping is identi-fied for possible circumvention of radiative-trapping limitations in larger volumes. Preliminary data on aluminum appear promising for shorter wave-length extrapolation. The advantage of efficient x-ray cavities is apparent. Extension of the illustrative analysis provides directions for future quantitative measurements leading to large scale gain experiments.

Infrared heterodyne spectroscopy is an extremely useful tool for Doppler-limited studies of atomic and molecular lines in diverse astrophysical regions. The current state of the art is reviewed, and the analysis of CO2 lines in the atmosphere of Mars is outlined. Doppler-limited observations have enabled the discovery of natural laser emis-sion in the mesosphere of Mars and the discovery of failure of local ther-modynamic equilibrium near the surface of Mars.

Atmospheric'spectroscopy, employing the sun as a source, has been routinely used for a number of years as a means for identification and quantitative measurements of atmospheric species. Recent improvements in Pb-salt semiconductor laser technology when combined with infrared heterodyne technology provide the capability of obtaining solar spectra with sub-Doppler spectral resolution. In this paper we discuss ultrahigh resolution (0.007 cm-1) atmospheric solar absorption spectra that have been obtained from a tunable infrared heterodyne radiometer. The radiometer was developed for ground based observations in the 8 to 12µm region, and tunability is achieved through the use of Pb-salt semiconductor laser local oscillators (L0). Spectra have been obtained in a piece-wise fashion from 9.1 to 11.1 um using laser emission modes that exhibit characteristics suitable for LO operation. Spectra showing absorption features of HNO3, 03, CO2, and H2O are presented along with comparisons of experimental and synthetic spectra calculated using a line-by-line atmospheric transmission model.

The resolution in the image reconstructed from a far-field hologram is dependent upon recording the interference fringes within the envelope of the far-field pattern. The fringes are discussed in terms of their visibility and are used to show that the resolution is ultimately dependent upon the shape of the object rather than its size. Examples of spherical, square and rectangular particles are discussed in order to demonstrate this point.

This article describes a characterization of the wavefront aberrations introduced by some typical misalignments and fabrication errors of laser resonators incorporating reflecting axicons. A set of orthonormalized functions were derived and coded into a subroutine of a general purpose interferogram reduction program called MCI. Because squares of coefficients of orthonormal functions may be added to yield the variance of the wavefront, such functions are especially useful in quantifying contributions to the wavefront variance caused by departures from the ideal construction parameters. A description of parabola-parabola reflaxicons in terms of their resonator and beam parameters is given. The resulting system of equations determines a single parameter family of parabolas satisfying the first-order requirements on the reflaxicon. Simple relations between the resonator's linear measurements and inputs to a lens design code are derived. This makes for ready analysis of the resonators using the lens design code linked with MCI. Optical path difference fans and simulated interferograms are presented.

Lidar measurements of the worldwide movement of stratospheric aerosols produced by the 18 May 1980 eruption of Mount St. Helens are described. Ground-based and airborne measurements show that the layers below 20 km produced by this eruption moved in an easterly direction while those above 20 km moved in a westerly direction. The effluent at jet stream altitudes of 10 to 12 km circled the globe in about 16 days and the effluent at 23 km (the highest altitude recorded) circled the globe in about 56 days. Mass calculations, using backscatter-to-mass conversion models, indicate that approximately 0.5 X 106 metric tons of new stratospheric material were produced by this eruption. Even though this represents a 200% increase in North-ern Hemispheric aerosol, no significant long-term atmospheric temperature change should occur.

This paper presents veiling glare of various types of current lenses-wide angle, standard, telephoto, and zoom; introduces the effect of reflection in camera bodies; and proposes criteria for the assessment of veiling glare. Veiling glare does not differ significantly with focal lengths of lenses, but differs appreciably between manufacturers: less than 1% to more than 10%. The increase in veiling glare due to the reflection in a camera body differs with manufacturers: less than 1% to several percent. According to the results of comparison of the measured veiling glare values with actual pictures taken by lens-and-camera systems under test, the following criteria correspond very well to the actual photographic performance: veiling glare of not more than 1.5%, very good; between 1.5% and 3%, usually good; between 3% and 6%, usually poor, more than 6%, poor.

We examine the seasonal, day-to-day, and diurnal fluctuations of Cn2 using data from the mesosphere, stratosphere, troposphere (MST) radar at Poker Flat, Alaska. The radar has been operated in a nearly continuous mode since early 1979, with profiles recorded every 2 to 4 minutes. The results for Cn2 are presented at about 2 km height intervals from 4 to 20 km. It is found that the mean values of Cn2 in the troposphere are about 10 dB larger in summer than in winter at all levels. In the stratosphere the seasonal means are nearly the same. The diurnal range is about 3 dB in the troposphere during all seasons, and varies in the stratosphere from about 3 dB during winter to 10 dB during summer. The relationship of mean Cn2 with meteorological variables is discussed.

A new type of holographic optical element is demonstrated which combines some of the flexibility of computer generated holograms with the large space-bandwidth product and high diffraction efficiency of interferometrically recorded volume phase holograms. The optical element is recorded by subdividing a volume hologram film surface into numerous small areas (facets), each of which is individually exposed under computer control. Each facet is used to produce a portion of the desired final wavefront. This new method allows the rapid production of high efficiency, customized, space-variant optical elements. A holographic cylindrical lens which has greater than 90% light efficiency and forms a line focus on a curved surface is demonstrated.

An expendable, autonomous vehicle by definition and implication will require small, low-cost sensors for observation of the outside world, and interface to smart, decision-making avionics. This paper describes results of several interrelated charge-coupled device (COD) camera projects directed toward achieving such an integrated sensor package. A shuttered high-resolution CCD detector combined with a CCD analog frame store memory is described. This system results in a full television (TV) resolution, frame-rate-reduced, deinterlaced image. These image data are suitable for transform or differential pulse-code data compression as well as various other 3 x 3 element operators directed at extracting image intelligence for on-board decision making.

The concept of an outdoor interferometer is developed using, as a basis, a scatter-fringe interferometer. The purpose of this interferometer is not for testing any optics, but purely as a visual phenomenon. As such it could be installed in a large park or a science museum when constructed on a large scale.

Although the theory of partial coherence was formulated in a reasonably general form about a quarter of a century ago, it was not until a few years ago that this theory began to be applied to problems of radiation from partially coherent sources. In this review article, the properties of the radiant intensity generated by a planar source of any state of coherence will be discussed. It will be first recalled that the radiant intensity can be expressed as a two-dimensional spatial Fourier transform of a correlation function of the field in the source plane, averaged over the source area. The characteristics of the radiation from several model sources will then be analyzed. With the help of these results, certain equivalence theorems relating to the radiant intensity from planar sources of entirely different degrees of spatial coherence will be reviewed and the underlying physical principles will be elucidated. A number of illustrative examples will also be given. Finally some very recent work, which has led to the construction of planar sources with controllable degrees of spatial coherence, will be described. Experiments carried out with these sour-ces will be discussed; they verify the main relationships between the coherence properties of the source and the directionality of the light it generates.

Signals froM a solid-state electro-optical line sensor, which samples a two-dimensional image brightness function in time and space, can be digitally processed to extract the ground velocity vector of relatively slow, autopilot-controlled aircraft such as mini-RPVs (remotely piloted vehicles). This sensor can be rotated into the direction of motion by a stepping motor which is controlled by a computational unit using simple easily realizable algorithms to keep the sensor in alignment with the velocity vector as well as to compute its magnitude. Together with other instruments already installed on board the aircraft, this combination of sensor and computational unit may form an instrumentation setup which can be used in passive, autonomous navigation systems. Computer simulated experimental runs proved that a sufficient degree of directional sensitivity and overall accuracy can be attained with the proposed method.

I address myself to one of the greatest joys that befalls an editor and also to one of the greatest sadnesses. One of my great joys is the privilege of sharing my concerns as editor with my colleagues who edit other journals (John Howard of Applied Optics, Joe Goodman of the Journal of the Optical Society of America, etc.). Unfortunately, one of the concerns we have to share is a source of my greatest sadness as editor. For lack of a suitably comprehensive term, I use the term "journal gamesmanship." Journal gamesmanship is the fine and well-developed art of seeking inappropriate credit for oneself via publication in a technical or scientific journal. This can mean anything from overt plagiarism to deliberately inaccurate citations. If you are shocked that such things occur, III am pleased with your innocence. Even if you are not shocked, I hope to make you, aware of the many forms in which this unfortunate and ugly game can be and is played.