The technique of implanting silicon wafers with sufficient oxygen to form a continuous buried oxide (BOX) layer is known as SIMOX (Separation by Implanting Oxygen). SIMOX wafers present leading-edge semiconductor technology with a great need for on-line process control. Development of thin (80 to 200 nm) BOX is a primary step toward improved device performance and cost reduction. Tight control of the BOX properties, such as the implant dose, thickness, refractive index, and composition, is required in the production. A method to characterize non-destructively BOX layer by means of FTIR normal incidence reflectance spectroscopy has been developed with a particular orientation to in-situ applications. A data reduction procedure based on multi-layer model delivers thickness and dielectric function of a thin BOX layer, and enables one to measure the implant dose with a precision of a tenth of a percent. A compact and robust FTIR spectrometer from On-Line Technologies, combined with sampling optics and sensitive detection, provides excellent signal-to- noise ratio and is well suited for a coupling with oxygen implantation machines for in-situ process control.

A comparison of spectral diffuse reflectance between different national standards laboratories is being planned under the direction of the Comite Consultatif de Photometrie et Radiometrie (CCPR). A similar comparison of bidirectional reflectance distribution factor among laboratories in the United States in support of optical remote sensing measurements is nearing completion. Since this comparison provides valuable lessons for the one organized by the CCPR, pertinent results and their implications are presented.

Four methods for the measurement of absolute reflectance are described and compared, with particular emphasis on application to transmissive materials such as windows and filters. Three of the methods, the 'V-W,' 'V-N,' and goniometer based methods, have been in use for a number of years. The fourth is an integrating sphere method. The sphere system is used for both specular and diffuse samples but achieves its greatest accuracy in the measurement of specular reflectance and transmittance. A direct comparison of the sphere and goniometer methods is made on samples in the infrared spectral region.

The characterization of the spectral transmittance and reflectance of windows and other optical components is a basic and important measurement. In principal, the measurements are relatively straightforward. However, even with an ideal high- accuracy measurement system, the sample's scattering properties can render the measurement results inaccurate or easily misinterpreted. The effects of low levels of scatter from specular transmissive samples on optical property measurements are demonstrated in the infrared with specular and hemispherical detection instrumentation. Complete measurement of the reflected, transmitted, and scattered light from these samples is demonstrated in the infrared using a center-mount integrating sphere.

A Fourier-transform infrared (FT-IR) spectrophotometer system is used to measure the transmittance of infrared band-pass filters as a function of wavelength, temperature, and beam geometry. Measurements are performed using an f/4 beam geometry at normal incidence, or a nearly collimated geometry with variable angle of incidence. Blocking filters are used to expand the dynamic range of the out-of-band measurement to transmittances as low as 10^-6 with 4 cm^-1 resolution.

We have performed transmittance measurements of metal-film neutral density filters on ultrathin polymer substrates using both Fourier-transform infrared spectrometer and laser-based (3.39 micrometer and 10.6 micrometer) systems. The use of ultrathin substrates, free of etaloning effects over the 2 micrometer to 20 micrometer spectral range, allows the FT-IR and laser measurements to be directly compared. We discuss the evaluation of the uncertainties in the transmittance values in both types of systems.

A set of neutral density filters covering the optical density range of OD 1 through OD 10 has been designed and constructed for use as calibration and reference filters in the infrared. The filters are optically flat, with a variation of at most one OD within the spectral range of 2 micrometer to 25 micrometer. Many filters exhibit better than 0.5 OD variation. They each are constructed of a metallic film supported by an ultrathin (100 nm) polyimide film substrate that minimizes the chance of etaloning within the filter. The polyimide substrate is sufficiently robust to withstand handling in a laboratory environment and provide long-lived performance. This paper details the theoretical model used to determine appropriate materials for these filters, as well as the vacuum deposition processes developed to construct them.

The selection of thin film materials for use in far infrared filters is limited. While silicon can be used as a high index material in the far infrared, the suitability of low index materials is less understood. In this study, thin film materials with spectral transmission extending from 1 to beyond 30 micrometer are characterized and evaluated for use in Rugate and discrete interference filters. A materials selection matrix was developed, and five materials were selected for characterization. Transmission, reflection and absorption data are presented for AgBr, AgCl, KBr, CsI and CsBr as single material films, and as blends. These materials are characterized for stress, exposure to humidity, and color center formation when exposed to visible light.

Historically, the optical coating community has greatly improved the environmental stability of single and multilayer coatings through the incorporation of energetic processes into the deposition chamber. Typically three different methods are used to impart additional kinetic energy: (1) to the evaporant at the source, (2) to the evaporant while in route between the source and substrate, or (3) to the condensate at the substrate. One of the benefits of these energetic processes is the reduction of the spectral shift of the filter with changes in relative humidity. Typical spectral shifts can range from tens of nanometers with nonenergetic processes to less than tenths of a nanometer with energetic processes. This paper contrasts in-situ measured spectral shifts over the visible wavelength region of single narrow reflection band rugate coatings placed in an environmental chamber. Measurements were taken at room temperature while incrementally increasing the relative humidity from less than 2 to 90%. The measured rugate coatings were fabricated by three different processes: physical vapor deposition, ion-assisted physical vapor deposition, and sputtering. The spectral shift of the reflection band for the physical vapor deposition coating was 24.7 nanometers, as measured at the full-width-at-half maximum, and for the two more energetic process coatings less than 2.6 Angstroms, the resolution of our measurement.

The National Institute of Standards and Technology is developing an optical filter standard for calibration of the wavelength axis of near infrared (NIR) transmission spectrometers. A design goal for the initial candidate Standard Reference Material (cSRM) filter was to provide absorbance peaks evenly covering the spectral region between 800 nm to 1600 mm (12,000 cm^-1 to 6,500 cm^-1). The reproducibility of the peak location, for batch-certified filters, was to be better than 0.02 nm (approximately 0.1 cm^-1). Glasses with 1 to 3 mole % Yb₂O₃, Sm₂O₃, and Nd₂O₃, incorporated into a commercial lanthanum oxide glass were evaluated for this proposed optical standard. An initial batch of cSRM 2035 filters was prepared based on studies of glasses made and evaluated in our laboratory. An interlaboratory comparison study was initiated in February 1997 to evaluate the utility of these filters for the chemical, pharmaceutical, instrumentation, and regulatory communities. Information concerning peak-picking algorithms, wavelength coverage, geometry preferences, and other parameters was solicited from the users. Based upon input from the participants of this interlaboratory study, we are making several changes to make SRM 2035 more useful to our customers. Two of these changes are: (1) incorporating Ho₂O₃ into the glass to introduce an absorbance peak at approximately 2000 nm (approximately 5000 cm^-1) and (2) providing users with a standard center of gravity (COG) peak-picking algorithm to locate the absorbance peaks of the SRM filter precisely. Recent results have demonstrated that the COG method provides a 10 fold improvement in the precision of locating peaks compared with traditional peak-picking methods.

Two types of mirrors and a glass are used as Standard Reference Materials to calibrate the specular reflectance scales of optical systems. While calibrations of these materials are routinely performed using the 6 degree/6 degree geometry, there has been an increased interest in the optical radiation measurement community for additional bidirectional geometries such as 30 degree/30 degree and 45 degree/45 degree. This paper reports the results of specular reflectance measurements of first surface aluminum and gold mirrors and polished black glass at wavelengths from 250 nm to 2250 nm. Supplemental measurements of wavelength standards are included to provide a comprehensive overview of the standards available for calibrating spectrophotometers.

Two methods for absorption line (peak) evaluation based on center of gravity (CG) calculations are described and compared using spectra of the NIST standard reference material (SRM) 1921(a) characterization measurements. These methods are (1) calculating the CG of 50% of the absorption line and (2) an extrapolated center of gravity (ECG) method designed to determine the line minimum (peak maximum) location. Important parameters used in both methods are evaluated. The importance of the spectral data spacing on the accuracy of the CG calculation is examined in detail and quantified for the 1921a lines. The effects of the range of data as well as the fitting routine used in the extrapolation process (in the ECG method) on the final line minimum are examined. A comparison of the absorption line values determined from the SRM 1921(a) spectra by the two methods is presented.

We have measured the near-normal ordinary ray transmittance and reflectance of crystalline Al₂O₃ from 1.6 micrometer to 11 micrometer and temperatures from 296 K to 582 K. The absorptance, or emittance, is derived from 1-(T+R), where T and R are the measured transmittance and reflectance. The derived emittance curves are compared with the predictions of a multi-phonon model prediction. Generally, good agreement is found between the measured and predicted results in the region of the multi-phonon absorption edge.

A multispectral pyrometric technique has been developed for obtaining the temperature of many insulating materials which makes use of infrared spectral measurements in the two phonon region of these materials. In the two phonon region the emissivity is virtually temperature independent and the approach developed here requires only a single calibration point. The technique has been found to be simple, convenient, and accurate. A sensitivity of +/- 2 degrees Kelvin at 1000 K is demonstrated on an emission spectrum of sapphire.

This work surveys techniques to measure the absorption coefficient of low absorption materials. A laser calorimeter is being developed with a sensitivity goal of (1 +/- 0.2)X 10^-5 cm^-1 with one watt of laser power using a CO₂ laser (9 (mu) m to 11 (mu) m), a CO laser (5 (mu) m to 8 (mu) m), a He-Ne laser (3.39 (mu) m), and a pumped OPO tunable laser (2 (mu) m to 4 (mu) m) in the infrared region. Much attention has been given to the requirements for high sensitivity and to sources of systematic error including stray light. Our laser calorimeter is capable of absolute electrical calibration. Preliminary results for the absorption coefficient of highly transparent potassium chloride (KCl) samples are reported.

Two techniques for deriving refractive index from high- resolution interferometric infrared transmission measurements are presented. The general characteristics of these techniques are described. Artificial data are used to explore the sensitivity of these techniques to various error sources. Refractive index is determined from interferometric measurements of several materials, including diamond, cubic silicon carbide, yttrium oxide, and KRS-5. The described analysis techniques are applied in a complimentary way to develop temperature-dependent Sellmeier type refractive index models that give accurate dispersion and thermo-optic coefficients. For several of these materials our results are the first infrared measurements of temperature-dependent dispersion. Our results are compared to published refractive index and thermo-optic coefficient data when it exists.

A novel method for the measurement of the change in index of refraction vs. temperature (dn/dT) of fused silica and calcium fluoride at the 193 nm wavelength has been developed in support of thermal modeling efforts for the development of 193 nm-based photolithographic exposure tools. The method, based upon grating lateral shear interferometry, uses a transmissive linear grating to divide a 193 nm laser beam into several beam paths by diffraction which propagate through separate identical material samples. One diffracted order passing through one sample overlaps the undiffracted beam from a second sample and forms interference fringes dependent upon the optical path difference between the two samples. Optical phase delay due to an index change from heating one of the samples causes the interference fringes to change sinusoidally with phase. The interferometer also makes use of AC phase measurement techniques through lateral translation of the grating. Results for several samples of fused silica and calcium fluoride are demonstrated.

Time-resolved degenerate-four-wave-mixing (DFWM) techniques have been used to characterize the nonlinear optical response of a KNbO₃/KTaO₃ superlattice grown by pulsed laser deposition on a 1 mm thick, (001)-oriented KTaO₃ substrate. With a 30 psec pulsed laser, the difference in the nonlinear optical response between bulk KTaO₃ and the superlattice was measured. Results indicate that a significant contribution to the response signal is due to the KNbO₃ superlattice. The (chi) ⁽³) value was estimated to have increased by 2 orders of magnitude compared to the bulk crystal.

We discuss a procedure for making accurate measurement of the index of refraction, its dispersion, and its temperature dependence, in the deep ultraviolet (near 193 nm), using precision goniometric spectrometers and the minimum deviation method. Measurements of the indices of fused silica and calcium fluoride near 193 nm, with a fractional accuracy of 7 ppm, are discussed. These measurements revealed differences in the indices between different grades of fused silica. Accurate values of the temperature dependencies were determined from measurements of the indices at several temperatures in a 20 degree Celsius range about 20 degrees Celsius. A procedure to measure the index of calcium fluoride in the vacuum ultraviolet region (157 nm) using a N₂ purge housing is discussed.

We describe instrumentation that has been constructed at the National Institute of Standards and Technology (NIST) for measurement of the index of refraction of solid materials in the spectral region from 0.5 micrometer to 1000 micrometer using Fourier-transform based spectrophotometers and etalon samples. Preliminary index of refraction measurements have been performed on fused silica and arsenic trisulfide glass samples from 0.5 micrometer to 12 micrometer, and the results are compared to tabulated values on these materials.

A new 2-modulator generalized ellipsometer (2-MGE) is used to determine the optical functions of uniaxial materials. This new instrument measures 8 parameters, compared with two parameters measured by standard spectroscopic ellipsometers. These 8 parameters can be used to determine the 6 independent elements in the reduced Jones matrix describing light reflecting from a surface. For orientations of the optical axes significantly different from normal incidence, these measurements can be used to determine the optical functions of uniaxial materials. The resulting optical functions are the most accurate available for photon energies greater than the band gap (where transmission measurements cannot be performed), and they compare well with minimum deviation techniques which are more accurate for photon energies in the transparent region. Several examples will be given, including rutile (TiO₂), ZnO, and BiI₃.

A Fourier transform infrared (FT-IR) spectrometer-based broadband infrared polarimeter has been developed around a pair of high-quality Brewster angle polarizers. These polarizers consist of four Ge plates in a chevron geometry and have been measured to have extinction ratios of less than 10^-5 at four laser wavelengths from 0.63 micrometer to 10.6 micrometer. The polarimeter has been used to characterize wire-grid polarizers from 1 micrometer to 12 micrometer, as well as for full Mueller matrix determination from 1 micrometer to 5 micrometer using a rotating-retarder arrangement with a pair of MgF₂ retarders.

The nondestructive measurement of refractive index of transmissive materials using null polarimetry is simple, accurate and does not require much on sample preparation. In null polarimetry, the ellipsometric parameter (psi) for reflection from a sample is measured. (psi) for transparent material is defined by tan (psi) equals r_p/r_s where r_p and r_s are coefficients of reflection for the p- and s-polarization respectively. By choosing the angle of incidence (Theta) near the Brewster angle, refractive index can be computed from (Theta) and (psi) directly. The only requirement on the sample is that no back surface reflection is allowed to mess up the front surface reflection. Precision in the refractive index is about 0.0004. Spectra of refractive index for quartz are measured and compared with the spectra quoted from existing Handbooks.

Accurate measurement of polarization properties of materials in transmission is becoming increasingly important as polarization devices and effects are utilized in remote sensing, displays, and other applications. Polarization components in these systems require careful calibration and specification as a function of wavelength. This paper describes a Fourier transform spectropolarimeter, an instrument designed for measurement of polarization properties in transmission. Complete Mueller matrix spectra are acquired using a dual rotating retarder polarimeter placed in the sample compartment of a Fourier transform spectrometer. Several sets of detectors and sources for the spectrometer provide spectral Mueller matrix data from the ultraviolet to the infrared. We have extended data reduction algorithms and calibration techniques developed for an FTIR instrument to the new spectral regimes, including routines to analyze the Mueller matrix data in terms of diattenuation and retardance. This paper describes the instrument, the data reduction and analysis algorithms, and examples of data from several transmissive samples.

We have combined Brillouin scattering experiments with a single Fabry-Perot interferometer and a fundamental optics theory to determine the birefringence of single crystals. Double refraction in anisotropic materials give rise to doublet peaks in Brillouin spectra. With the incident plane orthogonal to the optic axis, the birefringence of the materials can be determined from one spectrum. We present the Brillouin spectra to confirm this fact for a single crystal (alpha) -LiIO₃. The birefringence of (alpha) -LiIO₃ is n_o - n_e equals 0.149 at 514.5 nm.

The focal shift of an optical filter used in non-collimated light depends directly on substrate thickness and index of refraction. The HST Advanced Camera for Surveys (ACS) requires a set of filters whose focal shifts are tightly matched. Knowing the index of refraction for substrate glasses allows precise substrate thicknesses to be specified. Two refractometers have been developed at the Goddard Space Flight Center (GSFC) to determine the indices of refraction of materials from which ACS filters are made. Modern imaging detectors for the near infrared, visible, and far ultraviolet spectral regions make these simple yet sophisticated refractometers possible. A new technology, high accuracy, angular encoder also developed at GSFC makes high precision index measurement possible in the vacuum ultraviolet by prism methods.

The focal shifts through optical bandpass filters built on color filter glass (CFG) substrates depend directly on substrate thickness and index of refraction. The filter set for HST Advanced Camera for Surveys (ACS) must have very tightly matched focal shifts. Knowing the index of refraction for substrate glasses allows precise substrate thicknesses to be specified. Unfortunately, index data is not provided by the glass manufacturer to the precision required to achieve adequately matched focal shifts. Therefore, the raw CFG materials for filters must be treated as unknowns with regard to refractive index. Using a simple yet accurate refractometer built at Goddard Space Flight Center (GSFC), indices of refraction were measured for approximately 30 different melts of CFG's from which ACS filters are made. In this paper, the process by which filters were made to have matched focal shifts is outlined, a compendium of all measured CFG index data is presented, and the variations of measured index from melt to melt of the same types of glasses are discussed and measured values compared to catalog values.

Refractive index measurements using the minimum deviation method have been carried out for prisms of a variety of far ultraviolet optical materials used in the manufacture of Solar Blind Channel (SBC) filters for the HST Advanced Camera for Surveys (ACS). Some of the materials measured are gaining popularity in a variety of high technology applications including high power excimer lasers and advanced microlithography optics operating in a wavelength region where high quality knowledge of optical material properties is sparse yet critical. Our measurements are of unusually high accuracy and precision for this wavelength region owing to advanced instrumentation in the large vacuum chamber of the Diffraction Grating Evaluation Facility (DGEF) at Goddard Space Flight Center (GSFC) used to implement a minimum deviation method refractometer. Index values for CaF₂, BaF₂, LiF, and far ultraviolet grades of synthetic sapphire and synthetic fused silica are reported and compared with values from the literature.

Various non-destructive optical characterization techniques have been used to characterize and identify synthetic gem materials grown from hydrothermal solutions, to include ruby, sapphire, emerald, amethyst and ametrine (amethyst-citrine), from their natural counterparts. The ability to observe internal features, such as inclusions, dislocations, twins, color bands, and growth zoning in gem materials is strongly dependent on the observation techniques and conditions, since faceted gemstones have many polished surfaces which can reflect and scatter light in various directions which can make observation difficult. However, diagnostic gemological properties of these faceted synthetic gem materials can be obtained by choosing effective optical characterization methods, and by modifying optical instruments. Examples of some of the distinctive features of synthetic amethyst, ametrine, pink quartz, ruby and emerald are presented to illustrate means of optical characterization of gemstones. The ability to observe defects by light scattering techniques is discussed.