The status of an effort by the International Standards Organization (ISO) to develop a standardized format for electronic exchange of data defining optical systems is presented. Interlinking of this effort with ISO 10303, the standard for the exchange of product model data (STEP) is also described.

SIRTF, the Space Infrared Telescope Facility, is planned to be the final one of NASA's four great observatories. It is a cryogenically cooled telescope designed to perform background- limited observations at all wavelengths between 2 and 220 micrometers . This stringent straylight requirement necessitates the use of infrared black coatings on all non-optical telescope surfaces. In order to make an informed decision, the SIRTF Study Office supported a long- range program to characterize the performance of a variety of black coatings over the full SIRTF wavelength range. Measurements of both specular reflectance and BRDF made by Sheldon Smith were incorporated into a model that predicts the blacks' BRDF coefficients at other wavelengths. The restrahlen reflectance peaks of Martin Black and Martin Infrablack at 2.2 and 5.4 micrometers are included in the model. An APART analysis of the current SIRTF telescope design was performed at wavelengths of 2.2, 3.5, 12.5, 60, and 200 micrometers . Evaluation of the relative performances of Martin Optical Black and Ames 24E2 on several critical surfaces led to the conclusion that the SIRTF straylight rejection could be enhanced by selecting different coatings for different surfaces. A very diffuse black is best on the mirror stops and secondary support struts, while a specular black could be a better choice for the vaned telescope barrel. Many coatings that are black and diffusely scattering at short wavelengths become quite bright and specular at long wavelengths. Extreme caution must be taken when using a black that becomes specular on any surface that can be seen from the telescope plane.

The performance of an optical sensor is limited by one or more noise sources. To obtain the expected high sensitivity commensurate to recent technological advances, it is necessary to suppress the `noise' attributed to stray light. After defining stray light and addressing its impact on sensor performance, general principles for stray light optimization are presented from the system engineer's perspective. Data from stray light analyses performed on the optical monitor of the X-ray Multi-mirror Mission (XMM-OM) and the visible channel of the Cassini visible infrared mapping spectrometer (VIMS-V) provide a basis for a comparative study between the traditional Ritchey-Chretien telescope and a contemporary off-axis re- imager that is inherently stray light inviolable.

There is a need for further work in characterizing and selecting spectrally selective coatings in two areas for ground-based telescope. The first is in low-emittance coatings for upper-end telescope and baffle structures. Low-emittance coatings are necessary to prevent overcooling of telescope structures relative to the ambient air temperature. The second area where more work is needed is the area of baffle coatings for infrared instruments. Detailed work is needed to evaluate which coatings are best suited for these applications and whether commonly available coatings such as anodized aluminum and commercially available paints are adequate for these applications.

A digital database with full user interaction is being developed to assist in the selection of black, white, reflective and transmissive spectrally selective materials. The database will include the optical, thermal, mechanical, physical, electrical and chemical properties of the surfaces and materials, as well as the space environment and contamination effects. The present paper presents an overview of the database project and describes in detail the atomic oxygen/vacuum ultraviolet sub-module of the space-environment module of the database. The purpose of the paper is to make the community aware of the project, to encourage participation, and to identify areas where community involvement is requested.

The technique of characterizing the surface roughness of smooth, clean, front surface reflectors from BRDF measurements is in common use and has been well documented in the literature. It relies on using the Rayleigh-Rice vector perturbation theory to obtain the surface power spectral density function (or PSD) from which surface statistics may be found. These calculations are restricted to smooth surfaces only, as defined by the Rayleigh criterion. A number of potential industrial applications that would benefit from the fast, non-contact aspects of scatter/roughness characterization have not been implemented because the smooth surface restriction is clearly violated. This paper offers a brief arm-waving explanation of why BRDF cannot be used to obtain the PSD for rough surfaces, explores increasing the wavelength and/or the incident angle as measurement techniques to extend the PSD (from BRDF) calculation to rougher surfaces, and presents data showing that TIS measurements (which do not require that the PSD be calculation) can be used to find the rms roughness of surfaces are less severely limited by the impact of the smooth surface criterion.

A description is given of the goniometric optical scatter instrumentation (GOSI) which has been developed at NIST for measuring the bidirectional reflectance distribution function (BRDF) from surfaces. The source, goniometer, and receiver are described. The systematic optical and electronic noise of the system is reported. The systematic electronic noise and background scatter have been reduced to allow a detection limit of 1 X 10^-9 sr^-1. This value is the Rayleigh scattering level from the air molecules in the room with a field of view of 7.2 cm at the sample position for 633 nm incident laser light.

This paper presents a description of a fully automated, computer-controlled hemispherical directional reflectometer (HDR). It fills the need in many fields of research and development for a device with HDR measurement capabilities which is state-of-the-art in wavelength coverage to 25.0 micrometers and higher, angular polarization resolved coverage 20 to 80 degree(s), partition of reflected radiation into specular and scattered components, and scattered transmittance. This performance is made possible using an 18' major axis electroformed gold-plated specular hemiellipsoid with a 1.8' foci separation. The radiance throughput to the FTIR of this design exceeds by a factor of more than 200 that of the usual diffuse gold integrating spheres. Derived data, based on reflectance and using provided software, includes the IR component of solar absorptance, the index of refraction n and k for dielectrics and conductors for Fresnel materials, and both directional and hemispherical emittance.

OMNISCATR 1000 is a second generation of a new generation of high resolution three dimensional scatterometers. The instrument can acquire 200,000 three dimensional scatter data points with a dynamic range of 10⁸. A description of OMNISCATR 1000 and its capabilities is presented. Data is also presented showing that the instrument's high speed data acquisition system has a measurement repeatability of 2.5%.

This paper reports on (1) the development of a fully optoelectronic BRDF sensor, and (2) first experimental results obtained with an automated setup consisting of the sensor, stages for specimen scanning, as well as PC hard- and software for the control of the setup and the evaluation of data. Main points covered are the construction of the sensor head, problems with the alignment of the hundreds of fibers needed, how to reach the necessary high dynamic range of the CCD camera employed, and the control of the laser diode.

APART is an industry standard computer program for calculating the stray light reaching the focal plane of a system. APART was originally designed to only calculate the stray light for axially symmetric optical systems. However extensions have been programmed into APART that allow an off-axis system to be modeled as well. This paper describes in detail the conventions and techniques that must be followed in order to accurately model an off-axis optical system in APART.

The Infrared Background Signature Survey (IBSS) Satellite was launched in 1991 aboard the Space Shuttle Discovery. At the end of this mission an on-orbit straylight experiment was performed to verify the off-axis rejection performance of the IBSS IR telescope. After this experiment the sensor was pointed into flight direction (RAM) for about 1 hour to study contamination effects. Back on earth the telescope was disassembled from the cryostat and the straylight performance was measured once again. Test results showed a surprisingly slight increase in the telescope point source transmittance (PST) compared to pre-flight measurements. This degradation mainly was caused by enhanced scattering from the scanning mirror in front of the telescope. For verification the scan mirror was removed and the bidirectional reflectance distribution function (BRDF) of the contaminated mirror surface was measured directly and compared to pre-flight measurements on the clean mirror surface. The BRDF shows a local degradation by a factor of up to 12 caused by micro-meteorite impacts. On the scan mirror surface some molecular contamination was found. Measurements show that the loss of IR reflectance in the 7 to 15 micrometers wavelength band is below 1%.

Mueller matrix polarimetry performed in the visible and near infrared indicates that an integrating sphere acts as an ideal depolarizer to the 0.5% accuracy of the polarimeter. The integrating sphere emits unpolarized light regardless of the incident polarization state.

It has been known for several years that not only a rough metallic surface but also a rough dielectric surface can produce an enhanced backscattering peak. Due to the difficulty in fabricating one- or two-dimensional dielectric rough surfaces with a high index of refraction or a free-standing film, no experiments have been able to reveal such a peak in scattering from a dielectric rough surface. In this paper we present experimental results of the enhanced backscattering from a free-standing dielectric film and compare these with theoretical analysis. The vacuum/dielectric interface is one-dimensional, randomly rough, while the second dielectric/vacuum interface is approximately planer. The numerical simulations for a one- dimensional, randomly rough free-standing dielectric film reveal some important information about the main mechanism for the enhanced backscattering peak, primarily the presence of the flat dielectric/vacuum interface. We believe that the coherent addition from a given light path that interacts with the rough dielectric surface at two different points due to its reflection from the back surface and its time-reversed partner leads to an enhancement of the intensity of scattering into the retroreflection direction with respect to the intensity of scattering into other directions.

This paper presents a novel measurement technique using a Mueller matrix imaging polarimeter to measure the near-angle polarization BRDF of reflective samples. A measurement is made on a diamond turned aluminum mirror with an rms roughness of 11.4 nm, and the results are interpreted.

A Whole Space Scatterometer ( WSS ) is introduced in details. The scattering measurement experiments have been done by means of this system. Some experimental results are presented as well. Keywords: BRDF , scatterometer

An up-to-date review of currently available black and reflective spectrally selective surfaces and materials in the former U.S.S.R. is given. They are primarily employed for stray light and thermal control purposes in applications such as concentrators, radiators, solar collectors, baffles, rust control, and thermostat heat control.

The measurement of wafer surface roughness has become of increasing interest in the semiconductor industry in the last year. This interest is driven by the need to reduce background `haze' associated with laser scanning particle counters, by the ever decreasing linewidth requirements and by a recent report that gate oxide breakdown voltage decreases as roughness increases. Scatter measurement offers the potential of being a fast, non-contact method of monitoring roughness; however, the ability to accurately calculate wafer roughness via scatter depends on various wafer surface characteristics. The paper presents data taken on a number of wafers and demonstrates that bare silicon scatters almost exclusively from surface topography and is isotropic over an appropriate spatial bandwidth, thus facilitating scatter measurement. Because silicon proved to be an excellent source of topographic scatter, an experiment was undertaken to compare the one dimensional roughness measurements made with an optical profilometer to the two dimensional (area) measurements made via scatter, and these results are also reported.

Advanced solar cells and optical detection devices incorporate surface texturing to reduce reflection of the incident radiation and, thus, enhance optical absorption. Using micromachining techniques, three different silicon surfaces were fabricated, optically characterized, and analyzed in terms of their ability to reduce optical reflectance. The fabricated surfaces consisted of: randomly sized and spaced pyramids (RSSPs), deep vertical- wall grooves (DVWGs) and porous silicon (PS). Three regions of the optical spectrum were investigated: visible (500 - 900 nm), near-infrared (1.25 - 2.5 micrometers ), and mid-infrared (2.5 - 12.5 micrometers ). A highly-polished, single-crystal silicon wafer was used as a reference surface. The following results were experimentally determined. The RSSP surfaces decrease the reflectance by more than 69% over the entire measured spectrum. The DVWG surfaces reduce the reflectance by 85% in the visible region, 34% in the near-infrared range, and 14% over the mid-infrared wavelengths. Both thin (pore depths less than 1 micrometers ) and thick (pore depths greater than 5 micrometers ) PS surfaces were investigated. The thick PS revealed better results compared to the thin PS, demonstrating 91% reflectance reduction in the visible region, a 7% reduction in the near-infrared range, and 53% reduction over the mid-infrared wavelengths.

Unusual variations in the BRDF levels of several IR-black coatings measured at specific IR wavelengths are presented to illustrate the different affects of roughness, thickness, and absorption upon coating reflectance.

With OMNISCATR's high resolution and three-dimensional light scatter measurement capabilities, a new method is now available for analyzing surface and material properties such as tooling or etching patterns, contamination, and bulk defects. Scatter data from patterned wafers, sub-micron grit particles, and defective interocular lenses is presented.

An attempt to interpret backscattering phase matrices of cirrus clouds measured with a ground-based lidar is undertaken in this paper based on a theoretical model of interaction between optical radiation and an ensemble of flaked crystals. Deviations of the diagonal elements from unity indicated that partides orientation differed from the horizontal one and the crystals had a prefered orientation at some angle with respect to the direction of sounding. Keywords: backscattering phase matrices, cirrus douds, lidar

A software tool called BRAVO (bidirectional reflectance analysis and visualization operations) has been developed for silicon graphics workstations to graphically display sampled BRDF data and to quickly generate highly detailed and complete BRDF data tables that are required by ray-tracing signature prediction codes such as LFWC's MCFAC. For a given incidence angle, measured BRDF values are displayed as colored dots located on a hemisphere at the angles they were measured. The color of each data point corresponds to its BRDF value. The hemisphere can be rotated in real time to be viewed from any angle, thus giving an undistorted 3-dimensional presentation of the data. In addition to displaying the raw BRDF data, a bicubic spline interpolation can be performed to generate a full hemispherical BRDF map with a selected 1 or 5 degree resolution. Interpolated data are represented by a hemisphere that is completely colored using Gouraud shading. Once interpolated, the data set is sufficiently resolved for BRAVO to calculate the directional reflectance (DR) value by numerical integration. If desired, BRAVO can then be used to normalize the BRDF to a known DR.