A simple technique to generate holographic optical elements with diffraction-limited performance at a wavelength different from the construction wavelength has been developed. The method consists of specifying the desired grating performance at the operating wavelength, selecting one construction beam, and utilizing a ray trace program to compute the aberrated construction beam required to create the hologram. A lens capable of focusing this aberrated beam to a point may then be designed using ACCOS-5. A point source used with this lens thus serves to generate the second required construction beam. A sample design which may be used to construct with 0.4579-μm light a grating to operate at 2.8 µm is presented.

The formation of a blazed holographic grating, using the interference of an ordinary plane wave with a surface wave is considered. The usual holographic recording arrangement has been modified such that a positive photoresist recording layer is coated on one face of a prism; one of the recording beams is totally reflected from the prism such that the surface wave thus formed enters the photoresist from the back side. The other recording beam also enters from the back side, but is an ordinary plane wave. The resulting interference fringes are inclined with respect to the normal. With this arrangement the profile can be contoured more precisely than usual and many variations in the shape of the profile are possible. Modifications of the method described here allow the formation of gratings on curved surfaces and in some cases correction for aberrations. Once a profile has been formed in this fashion in photoresist it is possible to replicate it exactly in a durable metal layer using electroforming techniques. Such gratings are applicable for use in specrometers where high beam intensities must be taken into account.

Diffraction gratings on the surfaces of optical substrates have been demonstrated to perform functions such as beam sampling and infrared polarization. These surface gratings are defined by holographic exposure and ion beam sputter etched into a gold layer on the substrate. The patterns can be designed with spatially varying periods to provide optical power in the diffracted beam and they can cover large areas on flat or non-flat surfaces. High grating accuracy and edge definition result in improved performance when compared to conventional fabrication techniques.

Photolithography with metallo-organic resists is a relatively new addition to photo-engraving technology, and involves the chemical incorporation of inorganic constituents into photopolymerizable organic compounds, so that the photoresist functions not merely as a masking material, as in conventional photolithography, but also as the mass transference vehicle itself. The deposition of thin structured films of metal oxides with this method has been accomplished, the metal-doped resist in each case being the metal acrylate in acrylic acid, except in those cases where the metal acrylate was insoluble. Polymerization was effected with uv irradiation. The criteria for depositing other classes of inorganic compounds are outlined.

When fabricating holographic gratings the exposing interference pattern must be stationary. Normally this is achieved by working in a very stable interferometric environment where special care has been taken regarding low dependence of temperature, stable mechanical and optical components. Despite considerable precautions in these respects, reproducible results are difficult to achieve, especially considering the fabrication of multiple exposure gratings i.e. Fourier synthesis gratings. In our laboratory we have developed a technique for fabrication of holographic gratings by using a reference grating and a servosystem to keep the interference pattern stationary. The reference grating monitors both frequency and phase errors. This method allows us to achieve a high outcome in fabrication without utilizing replicas. It is also possible to reproducibly make Fourier synthesized gratings with selectable phase between the different harmonics.

Photographic recording of interference fringe fields has long been recognized as a method of producing diffraction gratings, with the potential of avoiding residual mechanical effects that occasionally inhibit the performance of ruled gratings. Practical realization required the development of suitable light sources (in the form of ion lasers), and a photographic medium capable of accepting smooth, fine pitch modulation (in the form of photoresist). However, to expand from this base and produce high grade diffraction gratings requires much more than standard holographic techniques. Some of the techniques are described. Since reduction of stray light is one of the prime reasons for adopting a direct interferometric approach to making gratings, it follows that a corresponding figure of merit ought to be adopted, capable of being determined by a simple procedure. One such approach is suggested and results given. It indicates no difference between the performance of a master and high grade replicas derived from a chain of several generations, but does indicate a difference between holographic and mechanically ruled gratings.

During the past several years the Lockheed Palo Alto Research Laboratory has developed a capability to produce holographic optical elements using a variety of production techniques. Gratings produced have included reflective gratings using both overcoated photoresist and ion etched substrates up to 15 cm. in diameter. Conventional bleached photographic transmission gratings have also been produced for some applications. Methods in use at Lockheed are capable of producing extremely rugged gratings which can withstand both physical abuse and high incident flux levels. Photoresist coating techniques have been developed which are sufficiently precise that optical quality obtained with reflective gratings is limited primarily by the quality of the construction optics. Both high and low efficiency gratings have been produced for a variety of applications. This paper presents an overview of Lockheed holographic grating technology.

Based on long experience in the field of holography and recording materials, research on holographic gratings has been pursued at the Institute of Optical. Research for a number of years. Grating production tech-niques have been developed including an interferometric setup with microcomputer control of exposure and fringe stabilization as well as methods for grating performance evaluation. A specialty is the synthesis of blazed grating profiles from successive exposures of their Fourier components. Theoretical studies based on electromagnetic theory and experimental investigations are carried on aiming at the optimization of these Fourier blazed gratings. Finally, as an example for the design flexibility of holographic gratings, a multiple grating flame photometer for the simultaneous determination of five elements is presented.

A technique has been developed for producing transmission diffraction gratings suitable for use in the soft x-ray region. Thin self-supporting films of a transparent material are overlaid with several thousand opaque metallic strips per mm. Gratings with 2100, 2400, and 5600 1/mm have been produced and tested. Representative spectra over the wavelength range from 17.2 to 40.0 nm are given for a grating consisting of a 120-nm-thick Al support layer overlaid with 2400, 34-nm-thick, Ag strips/mm. The absolute transmittance is rblp at 30 nm, and the efficiency in the first order is ~16%. The observed resolution of rb2A is acceptable for many of the potential applications. These gratings have several advantages over the two presently available alternatives in the soft x-ray region (i.e., reflection gratings used at grazing incidence and free-standing metallic wire transmission gratings). Fabrication is relatively quick, simple, and cheap. The support layer can also serve as a filter and help conduct excessive heat away. Higher line densities and hence higher resolutions are possible, and when used at normal incidence the spectra are aberration free. Suitable materials, component thicknesses, and line densities can be chosen to produce a grating of optimum characteristics for a particular application.

Nonlinear holographic gratings are of interest in laser systems for sampling beams from the primary mirror of a large beam expander. The sampled beam is then used for wavefront control purposes. This paper discusses the optical design and geometrical properties of the grating and its construction optics. The design and performance of a 30-cm aperture bread-board covering a 4-inrad field of view with an 8X, f/1.5 beam expander are then discussed. The wavefront aberration differences between the sampled and laser beams are corrected to within a maximum error of 0.3 µm.

Ion beam sputter etching has proven to be a superior technique for producing grating sampling mirrors for large optical systems. The patterns to be etched are defined by a photoresist masking film on the mirror surface. Grating patterns have been produced on laser mirrors by replication of diamond-scribed master patterns, while holographic construction has been used to produce linear and nonlinear gratings. The microscopic details of ion etched grating profiles show that the process is capable of high resolution pattern delineation and large area device fabrication.

Blazed ion-etched holographic gratings with a high absolute diffraction efficiency, good diffracted wavefront, high resolution, and low stray light have been produced. The performances were proved to be the same as, or superior to, commercially available blazed gratings produced by a ruling technique.

This paper outlines how ray trace techniques can be used to predetermine new configurations of monochromator and spectrograph gratings. Examples of Rowland Circle aberrations vs. aberration corrected configurations are given in which it has been seen that astigmatism can sometimes be reduced by over a factor of 10. When non-Rowland Circle configurations are used, astigmatism can often be reduced to zero. This is demonstrated in a new type of grating that acts as a scanning flat field spectrograph operating at better than F3 from 600-1200nm.

Diffraction gratings have been evolving steadily over the last ten years. Modern ruling engines have permitted classically ruled gratings to be more efficient with flatter diffracted wavefront than ever before. Examples include sophisticated laser gratings with up to 97.5% efficiency and flatness of better than λ/3 in 17th order 6328X. Holographically recorded diffraction gratings continue to evolve with the development of blazed plane gratings and with groove densities of up to 6000g/mm. Concave holographic gratings now range from toroidal aberration corrected gratings,for use in the soft x-ray, to flat field spectrographs and scanning spectrographs operating out into the infra-red.

The differential method developed in the seventies reduces the problem of diffraction of light by a periodic structure to the numerical integration of a set of coupled differential equations. It works both for perfectly conducting gratings and for finite conductivity gratings, including dielectric ones. It can handle very easily dielectric overcoatings deposited on top of gratings and gives very low computation times. The principle of the method is explained and a review of its extensions and possibilities is given.

A simple low-cost non destructive method has been developed for reconstructing grating profiles. It is based on an inverse scattering, electromagnetic rigorous theory. A computer program has been written for metallic gratings. It makes use of an efficiency curve in a constant deviation mounting and in TE polarization, and reconstitutes the grating profile. Thus the implementation of the reconstruction requires only optical measurements which can be easily performed and do not damage the grating surface. The program has been tested both on numerically simulated data and on actual physical measures, and gives good results.

A method for determining the groove depth of a sinusoidal holographic grating is presented, which makes use of a laser to measure the efficiency in two simple geometries; at normal incidence, and in Littrow configuration. The efficiencies measured are compared to theoretical values to determine the groove depth. Measured efficiencies are plotted versus groove depth and appear to fit very well to corresponding theoretical curves. Some gratings were also studied by a scanning electron microscope. The groove depths measured from the SEM photographs are compared to those derived from efficiency measurements.

In Integrated Optics, the coupling of one mode propagating into a multimode slab waveguide to a single mode slab waveguide can be achieved by the use of a grating with varying period. A method to compute the coupling efficiency of the grating is proposed here. The fir t step is based on the differential formalism of diffraction and gives phenomenological coefficients characterizing the grating. Then an adiabatic approximation is used to take into account the variations of the grating period and the coupling coefficient is found by the numerical integration of a set of two coupled differential equations along the length of the device.

A new exact coupled-wave analysis is applied to the diffraction of electromagnetic waves by longitudinally-periodic media (reflection gratings). The analysis is formulated in a simple state equation matrix form easily implemented on a digital computer. The relative intensities of the two waves, the diffracted (reflected) and transmitted waves, are calculated for a wide range of parameters. These exact results are then compared to results obtained with the approximate 1) two-wave modal analysis, 2) multiwave coupled-wave analysis, and 3) two-wave coupled-wave analyses. Exact calculations for even-order Bragg incidence (which can not be handled with approximate coupled-wave analyses) are included.

A Numerical Solution for the interacting TE mode fields of a surface grated dielectric slab waveguide between parallel perfectly conducting plates is presented. The structure is assumed to operate in the reflection mode (where the dominant coupling is between counter-running film guided waves). The structure between plates provides an approximation to the open structure problem, where the plates are absent and the substrate and superstrate are both infinite in extent. With this approximation to the open structure it is possible to handle some cases of operation of the open structure near cutoff.

Outlined here is a derivation of the Rayleigh-Fano equations and how they may be applied to light scattering from periodic and random surface irregularity.

General slanted planar gratings bounded by two different media, have been analyzed using a new rigorous coupled-wave approach. The analysis is unifying and is formulated in a simple matrix form easily implemented on a digital computer. Sample calculations for transmission, slanted, and reflection gratings are presented. This new approach is compared to the widely-used modal approach and to the approximate coupled-wave approaches. It is shown that, for the present coupled-wave approach, solutions are easily calculated for general slanted gratings whereas solutions using the modal approach are available only for unslanted (pure trans-mission) gratings.

The existence of a comnlex pole of the reflection coefficient of a metallic plane, or of the zero order efficiency of a metallic grating, implies the existence of a homogeneous solution of Maxwell equations. Such a solution, which exists in the absence of any incident wave, is a guided wave on the plane or corrugated surface and is responsible for several strange phenomena such as grating anomalies, total absorption of light by a grating, or the coupling of a laser beam into an optical waveguide by means of a photoresist grating. For TM polarization, the guided wave is usually due to plasmon resonance in the metal. But similar phenomena can be observed for TE polarization provided one superimposes a dielectric overcoating with convenient thickness on top of the metallic grating.

The differential method used to compute the field diffracted by a grating is based on a shooting method which requires the integration of a set ordinary differential equation from the bottom up to the top of the grooves. Numerical instabilities appearing for dielectric gratings with grooves deeper than the grating period are reduced if a formulation using two simultaneous counter-running numerical step-by-step integrations is used. Such a formulation is devised here for the TE, TM and general (conical diffraction) cases. Numerical examples are given to demonstrate the improvement of the method.

The Lau effect is observed when a double-grating pair is illuminated with spatially incoherent light. It would be of interest to generalize this experiment to include illuminating fields which have some degree of spatial coherence. To gain some insight into the changes the intensity distribution undergoes as the degree of spatial coherence is varied, we consider the special case of completely coherent illumination. This particular problem is easily discussed in terms of Fresnel images where it is found that the Fresnel image planes are defined by distances which are identical to the allowed grating separations in the incoherent Lau experiment. This suggests an interesting relationship between the nature of the fields in the incoherent Lau experiment and those in the coherent formation of Fresnel images.

The possibility of perfect blazing for infinitely conducting gratings used in non-Littrow mountings has been shown recently. This study is devoted to a thorough investigation of this interesting property for sinusoidal and echelette gratings. We show that most commercial gratings can exhibit this property.

On the basis of a simple model for diffraction by the groove, we show that the efficiency of an echelle is high in the Littrow arrangement, but becomes markedly less if the angle of deviation between the incident and the diffracted beams is increased. We also show that the height and width of the spectral image change if the directions of incidence and diffraction are interchanged, but that the efficiency remains the same. In general, the direction of maximum efficiency does not coincide with the blaze direction, defined as the maximum of the envelope of the diffracted-light distribution function. The difference depends on the mode of operation of the spectrograph (scanned or stationary spectrum) and typically changes from a fraction of a degree at high orders in the UV to several degrees at low orders in the IR. Experimental evidence agrees qualitatively with these calculations, but a more refined diffraction model may be needed for a quantitative interpretation.

Power losses in lamellar gratings per groove length are obatined by integrating the square of the tangential component of the magnetic field, obtained from the infinite conductivity solutions, along the grating profile. The groove fields for the perfectly conducting grating are generated by matching a superposition of diffracted plane waves above the grating to an exact solution of the groove boundary value problem for each polarization. Diffraction effects in the groove energy density and in the power losses are clearly evident.

A dichroic (or multichroic) beam splitter operating in the high energy laser HEL environment is called a shared aperture component and is becoming an increasingly desirable component in the design of HEL systems. At present, there are four basic types: Buried Short Period (BSP) grating, Buried Long Period (BLP) grating, Dichroic Beam Splitter (DBS) and Component Interlaced (CI) grating. The BLP and CI gratings are new types of grating that have recently been proposed and are currently under development. The four basic shared aperture components and their characteristics, their design and fabrication issues, and present technology status are described in this paper.

The ruling of a diffraction grating on two unusual surfaces will be described, and the techniques used are dealt with in depth.

A technique to measure the efficiency of diffraction gratings in the vacuum ultraviolet spectral region at any angle of incidence has been developed and will be discussed briefly. The measurements show that concave gratings do not have a uniform efficiency over their surfaces, primarily because of the change in blaze angle across the surface. Examples will be shown of results obtained using both conventionally ruled, and holographically recorded, gratings. A short discussion of stray light will be given, followed by a description of the type of contamination found in laboratory instruments and its effect on the efficiency.

One type of aperture-sharing device, the buried long period grating (BLPG), is described in this paper. The BLPG functions as a buried segmented mirror whose primary function is to spatially redirect, by reflections, an antiparallel laser beam and its corresponding low power broad band LWIR (long wavelength infrared) return beam. The aperture sharing unit consists of a pair of BLPGs, the second BLPG being used to restore spatial coherence across the LWIR wavefront. Other system functions of the BLPG such as autoalignment and beam sampling are discussed. The optical performance of the device is discussed in terms of energy losses due to material dispersion diffraction loss, degradation of resolution resulting from diffraction, segment fabrication tolerances, and thermally induced structural deformations due to laser beam heating. Both transient and steady-state thermal and structural analysis were performed on the device. One result from the analysis was the value of the burying dielectric thickness above the segment tips that minimized the stress within the device under laser beam irradiation. Fabrication consisted of separately tooling segmented surfaces in the cooled substrate and in the burying dielectric (CVD ZnSe and ZnS) followed by application of a metallic coating. These two segmented surfaces were joined with an appropriate bonding agent. The critical fabrication step is to use the bonding materials that have the following properties: (1) approaches full cure during fabrication, (2) minimum of outgassing with temperature and with time, (3) stable with aging (minimize surface distortion), (4) high thermal conductivity, and (5) flexible bond line to absorb thermal expansion mismatch between the dissimilar substrate materials. The exposed dielectric surface is polished flat, vacuum baked, and dichoric coated to reflect a laser beam and transmit a LWIR beam. Some top surface distortion is introduced during vacuum baking and during dichroic coating. Present work is towards reducing these fabrication temperature deformations by accurately mixing the bonding components to give different compositions. Preliminary work indicates good device performance in a laser environment.

Grating efficiencies in the vacuum ultraviolet have historically ranged up to 42% absolute on plane gratings overcoated with AIMgF2 for 1216A. This has been primarily achieved with spacings of 1200 1/mm to 3600 1/mm at blaze angles of 4° and greater. Gratings with less than 1200 1/mm at blaze angles of 2° and below have shown to reflect 10 to 30%. Gratings finer than 360C 1/mm were, (until now), only available when holographically produced. A better understanding of the factors limiting groove smoothness has made it possible to rule improved diffraction gratings for the vacuum ultraviolet. At 200 1/mm we have achieved absolute efficiency of 63% @ 1216A and with 6000 1/mm, 33 to 35% @ 1216A. These improved efficiencies have been possible on spherical and non spherical surfaces.

Three 30-cm mosaic gratings are being built for the Coude spectrograph of the Canada-France-Hawaii 3.6 meter telescope. The largest mosaic is 30 by 60 cm and is composed of four 15 by 30 cm echelle gratings. The individual gratings have coarse, fine, and super-fine adjustments. The alignment can be checked, and corrected if necessary, by one person in a few minutes. An earlier version of these mosaics has been in operation at the Dominion Astrophysical Observatory for many years and has proven to be practical and popular with the astronomers.

We made a first success to observed a diffusion constant of excitonic molecules in CuCl by a tunable picosecond transient grating method. This method is proved to be a powerful method to examine the spatial diffusion of uncharged particles like excitons and excitonic molecules in solid states.

The nole grating beam sampler consists of a uniform array of small circular holes in a highly polished mirror. When used as a turning flat in an HEL optical train, it produces a multiplicity ot angularly separated low-power replicas of the HEL beam in both the transmitted and retlected uirections. It thus provides the opportunity to perform many simul-taneous diagnostic tests such as power monitoring, bore-sight alignment, jitter sensing, wavetront sensing, power-in-the-bucket measurements, and spectral purity measurements in real time during HEL operation on a non-interference basis with the intended mission. The principle of the hole grating beam sampler will be discussed in detail and several relationships usetul to the HEL systems engineer will be derived. The capabilities and limitations of this versatile HEL diagnostic tool will then be discussed in the context of several specific applications.

Scatter from high efficiency, reflective diffraction gratings has been characterized. Three major types of scatter are identified: (1) random, which occurs over 27 s.r., (2) band or ghost scatter which occurs in the plane of incidence and (3) structured scatter which is a symmetrical pattern repeated about each order. Measurements were taken at 10.6 pm on gratings made by ruling, ion-etching, holography, or a combination of these techniques. We have found that the characteristic scatter from these high efficiency gratings depends strongly on the way the gratings are fabricated.

Light diffracted from a high efficiency, reflective grating may undergo a phase shift which depends strongly on the incident polarization. If the incident wave includes both TE (E // groove) and TM (El groove) polarization, then the diffracted orders may be elliptically polarized. This effect is of special interest in curved-line (holographic) gratings in which the eccentricity of the ellipse may vary across the diffracted wavefront. In this paper the existence of a substantial phase shift between the two polarization is demonstrated in gratings with a period-to-wavelength ratio less than one. Measurements are made at 10.6 µm on both ruled and ion-etched gratings. Comparison with theory shows that the measured effect is due to groove shape rather than to finite conductivity of the substrate.

In a recent publication Ushioda et al. (Phys. Rev. B. 19, 8, (1979), 4012) (henceforth referred to as I) reported an experiment in which Raman excitation of surface polaritons was performed using several rough surfaces. The authors of I observed an increase, with surface roughness, of the Raman scattering intensity, but were unable to give a theoretical explanation of this surprising effect. We suggest an explanation which is based on the similarity existing between Raman excitation of surface polaritons of frequency w along a grating and grating generation of surface polaritons using an incident E.M. wave of the same frequency co. We determine the surface polariton wave along the grating and find a strong enhancement of its intensity when increasing the groove depth. Thus there is a good qualitative agreement between our results and those published in I. This allows us to show that the phenomenon observed by the authors of I is related to the existence of Wood anomalies of gratings.

The behaviour of classical gratings (echelette, lamellar and sinusoidal) is correctly described by present electromagnetic theories by means of which new interesting profiles and more elaborate Fourier gratings can be obtained. Confrontation of theory and experiment is critical in the optical field because the groove spacing is less than one micrometer and the profile is not always regular. On the other hand, it is possible to work in the microwave range (26.5 to 40 GHz) with isomorphic-gratings having periods of several millimeter and perfectly ruled profiles. Our experimental equipment consists of a tridimensional 3 m radius goniometer, placed in an anechoic chamber. The antennae for emission and reception are parabolic D = 60 A diameter mirrors. The measurements are obtained using a phase-amplitude receiver, a ratiometer and a chart-recorder made by "Scientific-Atlanta". The system of data acquisition and analysis is obtained with a "Hewlett-Packard 9825" minicomputer. The relative accuracy of the grating efficiency measurement is better than 3%. We have already studied echelette, lamellar and Fourier gratings and, recently, we have studied crossed-gratings (round-holed grids and planar distributions of pyramids or half prolate spheroids both intended for solar captation). Agreement between theory and experiment is excellent and this apparatus is very powerful for diffraction or diffusion effect measurements - this is very important when the grating models are not treated theoretically.

CC: I would like to ask the panel four questions of general interest, and since our time is rather limited, I would like to ask you to try to limit your comments to three or four minutes. The questions are the following: 1. How would you characterize the progress of grating technology over the past 5 years, particularly in the area of theoretical analysis, experimental applications, and diagnostics? 2. What are the areas that need innovative ideas and technical break-throughs. This question is addressed more for the benefit of younger people. Suppose we have, for example, a Ph.D. student wanting to do a thesis; in what areas would you like to suggest they put their study time in? 3. What are the major problems in the grating technology community? Do they include funding, work force (are we educating enough talent in the Universities?), industrial secrecy, government assistance, international cooperation, patent protection, or any other items? 4. What actions can you suggest to promote the welfare of the grating technology community? Has it been worthwhile to come to this conference? Are there some things that we can change? What recommendations do von feel we should make?

We describe a model which gives a general expression for the two-dimensional spectral properties of periodic structures of grains perturbed by random jitter. The theoretical formulation is valid no matter what may be the form of the grains of the probability density function of the jitter. The power spectrum of such arrays of grains is a mixed spectrum containing both a continuous term and a discrete line structure. As the intensity of the random jitter is increased, the relative intensity of the line components decreases. Experimental results, obtained with computer simulated arrays of grains, are in excellent agreement with theoretical model. Using Fourier techniques, experimental power spectra are obtai-ned by an analogic optical method (Fraunhoffer diffraction) as well as by computer calculations (Fast Fourier Transform). The results presented here permit a quantitative determination of arrangement quality of periodic structures, randomly perturbed by jitter.

In High Energy Laser (HEL) systems, there exist requirements for spectral beam splitting devices for purposes of beam control and diagnostics. This paper describes the development of one such aperture sharing component, called the Compound Interlaced (CI) diffraction grating. The CI grating is ruled such that a high frequency, visible to near IR wavelength grating is placed directly on top of a lower frequency, long wave IR grating. In a system configuration, the HEL beam is sampled with the long period ruling and directed toward a wavefront monitor or beam tilt sensor, while the specular reflection is sent through pointing optics to the target of interest. At the same time, shorter wavelength return energy from the target is sampled by the short period grating and is subsequently imaged by an appropriate sensor. Results of work completed to date show that indeed such a grating can be fabricated on a high power substrate and can yield enough efficiency for an operational environment. The paper addresses various design and fabrication issues including groove spacing and profile, blaze angles, apex angles, skew angles (of one ruling with respect to the other), sub-strate coatings and ruling techniques.

Moire topography is applied for the follow-up of scoliosis patients. The results are then compared with the X-rays. A special lamp and scale arrangement is utilized for patient alignment. It is suggested that this technique will be used for the detection of all orthopaedic defects.

Described here is the derivation of an expression designed to predict the angular distribution of light scattered from composite surfaces. The scattering is assumed to be the result of microroughness, either periodic or random, present at each interface of the composite surface. The theory retains the vector nature of the fields and allows complex optical constants. The angles of incidence and scattering or diffraction are arbitrary. The number and thicknesses of the layers in the composite surface are arbitrary. The primary restriction on the validity of the theory is that the incident wavelength λ >>δ where δ represents the root mean square (rms) roughness of any interface. This restriction therefore precludes the application of this theory to high-efficiency gratings. However, low-efficiency gratings, such as those designed for beam sampler applications, fall within the validity of the theory. Also, high quality optical components, such as laser gyro mirrors, typically have rms roughness values much less than a wavelength. Various aspects and applications of this theory have been published previously.

The magnitudes of various effects which may lead to wavefront errors in gratings ruled on the Harrison 'C' engine,and which are not corrected by the translation servo loop, are evaluated. It appears that thermal expansion is not a problem with the current level of temperature control (± 5 x 10 -3 C) and that variations in the refractive index of air could be compensated to the 10 nm level. However an interferometer which permits direct monitoring of the spacing between the diamond carriage assembly and the reference fused silica straightedge indicates larger wavefront errors may arise because of the present diamond carriage support.

During recent years, the technique to blaze holographic diffraction gratings has been developed considerably. In particular, reproducible methods using successive exposures enable one to superpose several harmonic to the fundamental. So, it is possible to obtain what we call Fourier gratings. We show that by using only one harmonic, it is possible to find groove profiles having efficiency curves very close to - or even better than those of ruled gratings.

The development of interferographic techniques has led to an improvement in the quality of gratings available for spectroscopy and has permitted the manufacture of entirely new types of gratings. Unfortunately different aspects of performance have frequently been studied in isolation and it is not always appreciated that they are interrelated. A dramatic improvement in say, the focal properties may be at the expense of reduced efficiency or dispersion. The relative importance of these factors and the extent of any overall improvement will depend strongly upon the design of the instrument and the purpose for which it is built. The purpose of the present paper is to review the contribution of interference grating technology to spectroscopy in the whole of the ultraviolet region. Special emphasis will be given to the properties of blazed gratings both made in photoresist and ion etched into the substrate. Plane and concave gratings may be made with blaze wavelengths between 300 nm and 3 nm. The efficiency is generally equal or superior to those of ruled gratings and this can sometimes, but not always, be combined with good holographic correction of aberrations.

Periodic surface defects in mechanical industry, caused for instance by cavitation, are very difficult to analyze when the size of the defects is too small for conventional methods of analysis. The use of coherent light with grazing angle allows us to process the diffraction phenomena through a Fourier transform device, to obtain data concerning the size, distribution, and shape characteristics of periodic effects. The results are very promising in geophysics for the study of natural periodic materials (surface and particle) and in the study of damage caused by cavitation in hydraulic equipment for nuclear power and in the petroleum industry. The data are analyzed with very simple equipment. Other applications of this process are possible. We are working on a coupling of computers for very fast and large scale automatized control.