Although optical scatter is a source of noise, limits resolution and reduces system throughput, it is also an extremely sensitive metrology tool and is being employed in a wide variety of applications both in and out of the optics industry. This paper is intended as a brief review of the current state of this important technology as it emerges from university and government laboratories to more general industry use. The bidirectional scatter distribution function (or BSDF) has become the common format for expressing scatter data and is now used almost universally. Measurements are routinely made at several laboratories around the country from the UV to the mid-IR. Data analysis of optical component scatter has progressed to the point where a variety of analysis tools are becoming available for discriminating between the various sources of scatter. Work has progressed on the analysis of rough surface scatter and the application of these techniques to some challenging problems outside the optical industry. Scatter metrology is acquiring standards and formal test procedures. The available scatter data base is rapidly expanding as the number and sophistication of measurement facilities increases. Scatter from contaminants, which is a key issue for space optics, is continuing to be a major area of work as scatterometers appear in vacuum chambers at various laboratories across the country. The current flurry of work in this growing area of metrology can be expected to continue for several more years and expand to applications outside the optics industry.

Several authors claim and use the concept that the BRDF of a good, clean optical surface is invariant with the angle of incidence. Data and theory are presented to show the conditions under which such an assumption is valid.

When performing scatter measurements, it is always difficult to acquire accurate scatter data close to the specular beam. Most scatterometers are unable to obtain scatter information closer than one or two degrees from specular. In nearly all cases finite detector apertures and instrument background levels are the limiting factors. Since it is impossible to obtain infinitely small detector apertures or scatter-free system optics, an alternative approach to this problem must be used. A wavelength scaling law based on Fourier theory offers such an approach. This paper presents wavelength scaling data with test wavelengths ranging from 0.325 to 10.6 gm. Upon verifying wavelength scaling over common spatial frequency bandwidths, it is shown that scattering information at small angles from specular can be predicted with a high degree of confidence.

This paper discusses expressions for the BRDF of a weakly inhomogeneous half space and contrasts them with the analogous results for topographic scattering.

The opposition effect manifested as a narrow peak in the angular distribution of the intensity of diffusely scattered light in the backward (antispecular or retroreflection) direction has been experimen-tally investigated. A monostatic bidirectional laser reflectometer was used to measure the opposition effect of gold surfaces under illumination of YAG and He-Ne lasers. The results are compared with a recent theory of the elastic scattering of light from a randomly rough metal surface that predicts such a peak in the retroreflectance direction which, under certain conditions, can be related to the localization of surface polaritons.

This paper examines the requirement for reflector "smoothness" that is imposed when BRDF data is used to calculate surface statistics. There are applications for use of these calculations at surfaces that appear rough at visible wavelengths (greater than about 300 angstroms). Wavelength extension into the mid IR and increasing the angle of incidence are the two techniques investigated. Experimental results are compared to two widely used diffraction calculations by using known sinusoidal gratings and the advantages and limitations of each are discussed. Extension of the calculations to surfaces that have surface features as large as 5000 angstroms has been demonstrated at a wavelength of 10.6 micrometers.

The galvannealing of mild steel is a development of the familiar galvanizing process in which a thin coating of zinc on the surface of the steel, produced by immersion in a bath of liquid zinc, provides protection from corrosion. The zinc coating enhances surface quality as well as provides physical protection and, if the coating is ruptured, provides electrochemical protection by acting as the sacrificial anode in the bi-metallic cell. In the galvannealing process as shown schematically in Figure 1, steel strip is continuously run through a bath of liquid zinc at 465°C. Then it passes through air knives which control the thickness of the liquid zinc film and is then passed through a gas-fired galvannealing furnace, which heats the coated sheet to approximately 550° C. At this temperature the diffusion of iron into the liquid zinc causes the formation of an Fe-Zn intermetallic layer which grows and penetrates the free surface of the liquid zinc. On emerging from the furnace, the strip is air-cooled by fans and then coiled.

The angular distribution of the light scattered by a rough surface contains information on the texture of the surface. Profiles of nine specimens were measured with a stylus instrument and angular distributions of the scattered light were measured with a detector. The rms roughness of a surface that has an identifiable specular beam can be determined from the relative intensity of that beam. The autocorrelation length and the parameters that define the autocorrelation function, as well as the roughness of rougher surfaces that produce no specular beam, can in principle be determined by fitting the distribution computed from a model of a random rough surface to the measured distribution. In practice, measurement errors and computation errors preclude the determination of these parameters by a least�squares fit. Angular distributions were also computed from the surface profiles using a simplified model of the electromagnetic scattering.

Empirical experimental scattering data from conventional optical surfaces is shown to exhibit shift-invariant behavior with respect to incident angle when plotted in direction cosine space. This implies the existence of a surface transfer function that completely characterizes the scattering properties of the surface, and permits the application of linear systems theory and Fourier techniques in modeling the scattering effects of optical surfaces. A theoretical basis for this behavior is illustrated by showing that scalar diffraction phenomena (conical diffraction from gratings) is shift-invariant with respect to incident angle only in direction cosine space, and surface roughness can be considered to be composed of a superposition of sinusoidal phase gratings. The fact that many optical surfaces of interest deviate from this shift-invariant behavior does not invalidate the usefulness of the linear systems formalism. The ideal behavior of a shift-invariant scattering process can still be used for making engineering calculations and retained as the reference from which scattering from real surfaces is compared. This is completely analogous to the universally accepted transfer function characterization of imaging systems in spite of the fact that few real imaging systems are isoplanatic (no field-dependent aberrations).

Scatter from Beryllium mirrors often seems to be higher than would be expected based on mirror surface roughness data. This paper verifies the effect and shows that it is more severe in the IR than in the visible. The implication is that the excess scatter is caused by mirror defects that are non-topographic in nature. The conclusion is that profile, or roughness specifications should not be used when low scatter is the requirement of concern.

Bidirectional Reflection Distribution Function (BRDF) facilities at ERIM have been employed since the late 1960s to characterize the spatial, polarization, and spectral content of the scatter from target/background materials. This paper explores the "lessons learned" over the years, concentrating on the characterization of calibration standards, the expected variation of BRDF of materials, and the utility of BRDF data in the prediction of material/complex object radiative transfer. Expected and unusual material characteristics as a function of wavelength and polarization will be reviewed, as well as the procedures that have been used to provide accurate and repeatable BRDF data. The laboratory equipment that has been used will be briefly discussed, emphasizing the necessary characteristics and functions of the hardware needed to gather valid BRDF data. Finally, the utility/assessment/requirement of BRDF data to support modeling activities will be presented from the "ERIM" image/sensor information exploitation standpoint.

This paper discusses methods of predicting the BRDF of smooth surfaces from profile measurements of their surface finish. The conversion of optical profile data to the BRDF at the same wavelength is essentially independent of scattering models, while the conversion of mechanical measurements, and wavelength scaling in general, are model dependent. Procedures are illustrated for several surfaces, including two from the recent HeNe BRDF round robin, and results are compared with measured data. Reasonable agreement is found except for surfaces which involve significant scattering from isolated surface defects which are poorly sampled in the profile data.

The BRDF of any material may be obtained using either broadband or discrete wavelength sources, eg. solar spectral distribution simulators or lasers. Presently, there exists some discrepancy in the interpreta-tion and comparison of measurements made with these two sources. A reconciliatory methodology is presented in lieu of the current disarray of attempts to correlate scatter information obtained with lasers with that obtained using solar simulators. A technique is offered which is capable of rendering the few BRDF data obtained at discrete laser lines as a viable source for comparison to solar simulators. The solar spectral distribution (at air mass zero) was approximated analytically and used as a weighting function for the spectral BRDF of several generic types of scattering surfaces including white and black diffusers and specular samples; this defines the analytic solar BRDF. By conducting a solar spectral distribution weighting on the BRDF data obtained at various laser wavelengths, the resulting (calculated) solar weighted BRDF

A Bidirectional reflectance distribution function (BRDF) error analysis is given. Errors in measuring each of the components of BRDF are analyzed and a total RMS error calculation is given. A computerized error analysis allows each of the terms to be tested for their effect on the total error. This shows that different error mechanisms contribute in different measurement regimes.

Polytetrafluoroethylene (PTFE), is a white fluoropolymer resin that can be represented by the chemical expression [CF2-CF2]fl. These resins are internationally used in the field of diffuse reflectance spectrophotometry. Many applications, such as 450/0° Bidirectional Reflectance Distribution Function (BRDF) standards, are dependent on a specialized method of sample preparation. An experimental method has been developed which includes a technique for transforming aggregates of PTFE resins into a fine high quality aerated powder. This paper documents our progress in the characterization of the properties of pressed PTFE powders for potential use in BRDF standards developement: selecting PTFE resins, pulverizing PTFE resins, pressing PTFE powders, and measuring the BRDF's of samples with different surface conditions.

A standard is proposed for specifying surface roughness of optical elements to enable the control of scatter produced at optical surfaces. This scatter reduces system MTF, and signal-to-noise ratio. Such a standard must not be arbitrary but must be based on form, fit or function rather than convenience since available instruments can measure scatter or roughness. A roughness standard that can provide this is the one-dimensional surface Power Spectral Density (PSD), S1(fx)' (p,m3), where f is a one-dimensional spatial frequency (pm-1). The standard consists of four numbers: A the proportionality constant (.1m3+13), B a frequency exponent, C the minimum spatial frequency (Am-1) and D the maximum spatial frequency (Am-1). PSD can be bound by the function A/0 over the spatial frequency range C to D. From this PSD the Bidirectional Reflectance Distribution Function (BRDF), RMS roughness and autocorrelation length can be calculated. An experiment was designed to create a database of A and B for frequently used IR materials, glasses and reflective materials. Experimental data appears to confirm the potential viability of such a standard as refined by later validations and data additions. Variations of this standard exist for BRDF and two-dimensional PSD.

High-performance baffles are required in the operation of space sensors mounted aboard a satellite to track stars for attitude control or to identify the sky region aimed by a paralleled X-ray telescope. For example, on a typical X-ray observation mission, the star sensor shall identify stars in a 8 deg by 8 deg field of view down to the 6th magnitude, even when very bright sources (as the sun or the earth horizon) are only 10-15 degrees off the field of view. This corresponds to attenuate stray light down to approximately 10-9, what calls for a very sophisticated design of the optical baffle and also is an unusual requirement for the measurement of attenuation in the test-laboratory to validate the baffle before launch.1,2.

A method to generate a transfer function accounting for instrument measurement non-linearities is given. The BSDF instrument itself is used to make two measurement scans. One of these scans is taken at normal incident power and the second with a neutral density filter in the optics chain. Using the information generated by these scans, and assuming that the system is linear over some range of its operation, a transfer function may be generated to characterize the system and to allow non-linearities to be compensated for.

BRDF at 3.39 microns was measured on silicon carbide and aluminum foam and on 401C10 black paint. BRDF of the black paint increases by a factor of 100 at glancing angle. BRDF of the foams increases by less than a factor of 10 at glancing angle.

Optical baffle materials will play a critical role in meeting specifications for off-axis stray light rejection and contamination control for a number of planned space-based telescopes. Spire has been developing new baffle materials to meet those specifications. The purpose of this paper is to present the results of optical scatter and reflectance measurements for a number of currently available baffle materials and some new baffle materials developed at Spire [1]. Bidirectional reflectance distribution function (BRDF) measurements were performed in a fully automated, in-air scatterometer at two wavelengths, 632.8 nm and 10.6 microns [2]. BRDF data is presented as in-plane and out-of-plane scans over a direction cosine range of + 0.8. Total hemispherical reflectance (THR) measurements were carried out using a semi-automated spectrophotometer with an integrating sphere over a bandwidth of 400 nm to 1000 nm using a Xenon arc lamp as the source and at 3.39 microns and 10.6 microns using laser sources. A discussion of the performance of these optical baffles will be presented based on the BRDF and THR data, and scanning electron microscope (SEM) micrographs of the baffle surfaces.

Perkin-Elmer's Applied Optics Operation recently delivered several prototype wide-field-of-view (WFOV), F/2.8, 250 mm efl, near diffraction limited, concentric refractive lenses to Lawrence Livermore National Laboratory (LLNL). In these lenses, special attention was paid to reducing stray light to allow viewing of very dim objects. Because of the very large FOV, the use of a long baffle to eliminate direct illumination of lens edges was not practical. With the existing relatively short baffle design, one-bounce stray light paths off the element edges are possible. The scattering off the inside edges thus had to be kept to an absolute minimum. While common means for blackening the edges of optical elements are easy to apply and quite cost effective for normal lens assemblies, their blackening effect is limited by the Fresnel reflection due to the index of refraction mismatch at the glass boundary. At high angles of incidence, total internal reflection (TIR) might occur ruining the effect of the blackening process. An index-matched absorbing medium applied to the edges of such elements is the most effective approach for reducing the amount of undesired light reflected or scattered off these edges. The presence of such a medium provides an extended path outside the glass boundary in which an absorptive non-scattering dye can be used to eliminate light that might otherwise have propagated to the focal plane. Perkin-Elmer and LLNL undertook a program to develop epoxy-based dye carrier compounds with refractive indices corresponding to the glass types used in the WFOV lens. This program involved the measuring of the refractive index of a number of epoxy compounds and catalysts, the experimental combination of epoxies to match our glass indices, and the identification of a suitable non-scattering absorptive dye. Measurements on these blacks showed Bidirectional Reflectance Distribution Functions (BRDFs) between 1.4 and 3.1 orders of magnitude lower than Perkin-Elmer's most common edge-blackening technique. Specular reflectance off the surfaces coated with the optimized dyed epoxy compounds ranged from 3 to 5 orders of magnitude less than the Fresnel reflectance from an uncoated glass/air interface.

Bidirectional transmittance distribution function (BTDF) measurements were made on several infrared transmitting materials, including zinc selenide (ZnSe), fused quartz (Si02), mono and polycrystalline silicon (Si), calcium fluoride (CaF2) and spinel (MgA1204). The measurement samples were one inch in diameter, and two or three different sample thicknesses were measured for each material. BTDF measurements were made with a helium neon laser operating at 3.39 microns, at a 10° angle of incidence. Significant variations in BTDF were found among samples that were expected to have the same BTDF levels. A correlation between surface characteristics (such as surface roughness, figure and irregularity) and BTDF was found, explaining many of the BTDF variations between samples of the same thickness and material. The effects of bulk scatter on BTDF were examined through BTDF measurements on samples of different thicknesses. The measurement system is described, and data in the form of BTDF vs scatter angle and BTDF vs sample thickness are presented and compared for all five materials.

The effects of extreme changes in temperature on the Bi-directional Reflectance Distribution Function (BRDF) of beryllium mirrors have been observed and measured using an unique infrared (10.6-micron) scatterometer [1]. This paper describes the experimental apparatus and procedures, qualifies its accuracy and repeatability, and presents the BRDF data taken on two Be mirrors, at 300 K and 20 K, during repeated thermal cycling.

BTDF at 3.39 microns was measured on ZnSe substrates and on substrates with 1/3, 2/3, and full multilayer coatings. The BTDF range for coated samples overlaps the range for the uncoated ZnSe substrate.

BRDF measurements, as a function of polarization state, have been performed on well-polished optical surfaces using an automated scatterometer. The samples were polished to surface roughnesses of less than. 5 Angstroms rms and overcoated with various multilayer dielectric coatings for high reflectance at 6328 Angstroms. The polarization state of the input beam was selectable between p and s and the polarization state of the scattered light was determined using an analyzer at the detector. Measurements were taken from 90 degrees to the surface normal to within 0.5 degree from the specular reflection for several angles of incidence. BRDF is plotted for all combinations of input and scattered polarization states with instrument signature removed.

The analysis of scattering test results often raises questions of whether facility or sample anisotropy is responsible for variation in data. The sample may appear macro-scopically isotropic yet, as in the case of a Si wafer, may affect results due to its crystal cleavage or orientation relative to observation direction. In addition, there may be point-to-point variation in sample surface characteristics leading to slightly different results depending on beam size or position tested. The relevance of these considerations can best be assessed when all parameters are tested in a matrix-like study. Other data which affect scatter are: Surface contamination, ellipsometry (depolarization effects), and surface profilometry (roughness). The scatter-test matrix (in addition to contamination ellipsometry, and profilometry data) for a 6.0 inch diameter wafer includes: Beam size (1.0, 2.0 and 5.0 inches), beam polarization (vertical vs horizontal), sample cleavage axis orientation with re-spect to detector sweep plane (perpendicular vs parallel), and beam band-width (full xenon arc vs 100 Angstroms wide and peaked at 5000 Angstroms). Similar tests were performed (except with the 5.0 inch beam) with 5.0 inch samples cleaved at (1,0,0) and (5,1,1) crystal orientations.

Ten surfaces were exposed to a variety of clean-room environments. Particle distributions were measured by a washing technique and BRDF curves were obtained. Correlations (and lack thereof) between the two sets of data are given.

A simplified model of scatter from particulate-coated optical surfaces has been presented formerly. Results using it are compared with measured data and with a more rigorous model that uses integrated Mie and imaging techniques.

At NASA's Goddard Space Flight Center (GSFC), Bi-Directional Reflectance Distribution Function (BRDF) is applied to characterize the scattering properties of optical and thermal surfaces. In addition, the Particle Fall Out (PFO) instrument (currently under evaluation) is used to determine the particulate contamination on surfaces. This paper describes both instruments and correlates the results from their empirical measurements. Both the BRDF and PFO instruments are located in a Class 1,000 cleanroom to minimize contamination. The BRDF instrument is completely automated and controlled by a personal computer. The FF0 is a scattering measurement instrument developed by SAAB and updated by Uramec (Bilthoven/The Netherlands) [1]. The PFO is used to determine the surface cleanliness level on a contaminated plate by measuring the scattered light due to particles on the plate. For this paper, black glass is used as the contaminated sample for both the optical measurements. The PFO and BRDF instruments are then utilized to measure the scattering of the contaminated sample. Results are compared and related to the surface cleanliness level as well as obscuration factor.

A model of the total surface BRDF (Bidirectional Reflection Distribution Function) of optical surfaces has been developed to account for forward and backscatter of light as a result of particulate contamination. Measurements of several different optical surfaces are presented before and after particulate contamination in clean rooms and the forward and backscatter components are described. The prediction of the total BRDF using the model is correlated to the data.

Mirror scatter is a very important parameter for ring laser gyroscopes. For this reason, the Northrop Research and Technology Center has built an automated scatterometer capable of performing raster scans as a means of producing spatially resolved scatter information. The apparatus is flexible, with a minimum spot size of 5 microns and a maximum data rate of 1.5 Hz. Particulate contamination has proved to be a very serious problem with these measurements. An attempt to clean the part will result in no fewer of these particles; they are merely moved to different locations. Thus the particulate contribution to scatter can often be greater than that from the "real" features. A means has been devised to take advantage of the fact that, though the particulate contamination can never be completely eliminated, specific particles will tend to move around when the part is cleaned. In order to implement this technique, a means is needed whereby the part can be removed from the scatterometer and cleaned. After cleaning, the part must be replaced in exactly the same position within the scatterometer as before. Comparison of two scatter plots, one made before the part was cleaned and one after, will reveal which scatter features are due to particulate contamination and which are not: those features that appear in both plots are taken as real features. Presented will be a discussion of the equipment needed to implement the technique described. Also presented will be a comparison algorithm which can be expected to yield statistically meaningful data even for a large number of data sets. Actual scatter plots demonstrating the effectiveness of the technique will also be presented.

Spaceborne optical systems designed for long-duration missions are susceptible to degradation from contaminants in the spacecraft environment. In order to assess contamination build-up rates and corresponding scatter changes, we have designed a BRDF measurement system for use in a high-vacuum (10-8 Torr), low-temperature (20K) environment. The system measures cryocooled optics at angles from near-specular (< 1°) to approximately 30° off-axis, at wavelengths of 0.633 and 10.6 microns. We describe the design characteristics of the instrument, and discuss preliminary experiments which demonstrate contamination build-up correlated with changes in the sample BRDF profiles. The current status of the instrument is reviewed and future plans and applications summarized.

A method is presented for estimating the cleanliness level of the air contained in a BRDF measurement facility. The use of HEPA filters is assumed and a set of reasonable assumptions are set which provide a minimum criterion for the class of clean room required for a given minimum measurable BRDF desired. The basis of the method is the use of Rayleigh scattering theory.

A test molecule Monte Carlo simulation algorithm was devised and tested to compute near equilibrium transitional flow and resulting mass flux on complex surface geometries. The results agreed, within the calculated statistical error of the simulation, with known analytical solutions at the free molecular limit, and gave satisfactory agreement near the continuum limit, when compared to a diffusion model with slip boundary conditions. The effects of the Knudsen number on dimensionless mass exchange factors are considered for slip flow in an aperture geometry. A variety of surface outgassing and surface adsorption-migration kinetics models can be mated with the test molecule simulation to compute surface deposition values. A multimolecular layer model with two-neighbor migration is considered as one such alternative for surface adsorption-migration kinetics. Calculations of surface deposition for heavy chain oil molecules, known as DC-704, are compared to experi-mental data, showing good agreement. This kinetic model can serve as a boundary condition when computing the exchange of mass among various surfaces.

This paper describes an efficient computational approach to determine the obscuration ratio (OR), or particle area coverage, due to surface particulate contamination. The analytical approach utilizes a multi-bin particle size distribution model with incorporation of Raab's particle shape data and Barengoltz's areal density integration method. With this approach, surface contamination involving a wide spectrum of sphere/cylinder particle shape, as well as particle size distribution, can be characterized with ease. The present method also permits establishment of a correlation between the MIL-STD-1246B cleanliness level and the more meaningful obscuration ratio. This correlation will yield useful and time-saving benefits for spacecraft contamination control. Overall, our analytical method using best-available particle shape/size distribution data has resulted in much lower OR values by as much as 32% reduction than previous predictions based on spherical particles. Also discussed in this paper is a numerical method to predict the bidirectional reflectance distribution function (BRDF) for spherical and cylindrical particles as well as particle-laden reflecting surfaces. The method encompasses Mie scattering, diffraction, and reflection solutions for spheres, and diffraction and reflection solutions for randomly oriented cylinders. The BRDF computational scheme complements the OR prediction model, in that the particle deposit quantity and particle-induced light obscuration-scattering characteristics can now be determined in an efficient, in-tandem manner.

The Air Force Wright Research and Development Center and the Arnold Engineering Development Center are continuing a program for measuring optical effects of satellite material outgassing products on cryo-optic surfaces. This paper presents infrared (4000 to 700 cm-1) transmittance data for contaminant films condensed on a 77 K geranium window. From the transmittance data, the contaminant film refractive and absorptive indices (n, k) were derived using an analytical thin-film interference model with a nonlinear least-squares algorithm. To date 19 materials have been studied with the optical contants determined for 13 of those. The materials include adhesives, paints, composites, films, and lubricants. This program is continuing and properties for other materials will be available in the future.

Recent developments in the manufacture of flight hardware have created a demand for new techniques for contamination measurements on optical surfaces. The stringent cleanliness requirements imposed by working with these optics prohibit traditional contamination testing. The handling of optical hardware restricts contamination inspection by standard procedures. In order to view and document surface cleanliness, new photographic techniques have been pushed to their limits to record the image of light scattered from particulate contamination on optical surfaces.

One of the most deleterious effects of spacecraft contaminant films is that they increase the solar absorptance of optics, such as silvered fused silica thermal control mirrors or solar cell cover slips. However, this effect cannot currently be predicted with precision. Here we discuss the design of a laboratory program to enhance the quantitative understanding of this effect, as determined by the composition of the contaminant film and subsequent simulated environmental radiation-induced darkening. This effort includes four major elements: the quantitative identification of the classes of organic materials likely to be precursors of photochemically deposited contaminant films; prediction of these materials' sensitivities to energetic irradiation in the space environment; measurement of rates of deposition and optical absorption spectra of photochemically deposited films on fused silica; and measurements of further film darkening by irradiation with electrons, vacuum ultraviolet light, and ions. Each of these elements is discussed. A set of organic materials that have been chosen as analogs for major classes of spacecraft contaminants is presented, including the rationale for their selection and a prioritization of their potential importance. Apparatus design and performance and early experimental results are also described.

A miniature quartz crystal microbalance (mQCM), called the MK 16 QCM Sensor by QCM Research, is fully described in terms of its temperature range (5°K to 360°K), its ability to raise the temperature of the crystals independently of the case (which is held at --.10°K) with zero to 1.5 watts of power, and be designed as a flight qualified unit. As a QCM sensor, the MK 16 not only measures the mass of contaminates that arrive with time (6.7 Hz per monolayer) but also by raising the temperature of the crystal, constituent gasses will be re-emitted from the crystal which can be further analyzed by QCM thermogravimetry (QTGA).

We present a summary of contamination monitoring methods currently being used on extreme ultraviolet (EUV) astronomy instruments and in EUV calibration facilities at the Space Sciences Laboratory, U.C. Berkeley. Methods include measurement of contamination-induced optical degradation on EUV witness samples as well as measurement and characterization of contamination on non-optical hardware. EUV witness samples, fabricated in the same manner as novel grazing incidence EUV telescope mirrors, are measured for reflectivity and scattering in the EUV range of 80 to 900 Å. to characterize the optical degradation effects of contamination in the EUV and to provide a basis for molecular contamination requirements of EUV instruments. Particle size distributions on cleanroom surfaces and particulate models are used to develop particulate contamination requirements of EUV instruments. Non-optical hardware on EUV astronomy payloads is then processed to minimize the potential to transfer contaminants to sensitive EUV space optics, and is monitored for particulate and molecular contamination by a variety of methods. We compare the efficiency and accuracy of these monitoring methods and recommend guidelines for contamination monitoring activities, and for developing allow-able contamination requirements for various phases of instrument processing, including fabrication, assembly and testing.

The results of a nationwide CO₂ BRDF round robin are presented. This study was conducted as a follow-on to a 1988 0.6328 ,um BRDF round robin.(1) Four master samples ranging in roughness from a diffuse surface to a 45 A rms mirror were measured at six scatter facilities. BRDF data in the forward direction for an incidence angle of 10° is compared from all participating facilities for the four samples. Unfortunately, the samples were lost during shipment between scatter facilities, and it was not possible to complete measurements at the 14 planned facilities.