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Current Directions

• Calibration Services. The Division provides calibration services and measurements in the areas of radiance temperature, photometry, spectroradiometric sources, spectroradiometric detectors, and optical properties of materials. The Division continues to increase its offerings of measurement services, with the newest being for specular gloss. The NIST facility for measuring specular gloss centers around a newly rebuilt reference goniophotometer — an instrument that makes precise measurements of reflectance of light from a surface at varying angles — and a newly created primary gloss standard consisting of three wedges of highly polished, high-quality optical glass. The new service offers measurement of gloss standards at the standard geometries of 20, 60, and 85 degrees, which are compliant with the International Standards Organization (ISO) and ASTM specifications.

  Additionally, clients can now access the status of their calibrations via the Internet. They are provided access to status information via NIST's secure web server using the Information System to Support Calibrations (ISSC), which is a web-based structured query language (SQL) database.

  The Division also has a quality system in place for its calibration services that is compliant with ISO Guide 25.

• Training. The Division offers short courses in photometry and radiation thermometry. We plan to initiate a short course in spectroradiometry covering both sources and detectors during the coming year. In addition, workshops were held the past year on non-contact thermometry and the modeling of color and appearance, which provided opportunities for interested industries to learn about NIST programs and to furnish feedback on their needs in these areas.

• Cryogenic Radiometry. The Division utilizes and advances the technique of cryogenic radiometry, which is used to relate optical power to the SI watt. For much of the optical spectrum and at most power levels, cryogenic radiometry yields the lowest measurement uncertainties among current technologies used for this purpose.

  The Division maintains an absolute High Accuracy Cryogenic Radiometer (HACR) as the foundation of the measurement chains for most of its photometric and spectroradiometric calibration services. The combined relative standard uncertainty of this facility is 0.02 %. A second generation HACR is being developed and built which will have improved utility, sensitivity, and accuracy.

  A second high-sensitivity cryogenic radiometer is used as the calibration basis for the Low Background Infrared (LBIR) facility, which provides calibrations, research and development for high-sensitivity infrared sensors. At the Synchrotron Ultraviolet Radiation Facility (SURF), a new monochromator-based cryogenic radiometer facility has been established to derive a spectral radiant power scale in the ultraviolet and to serve as a calibration facility for transfer-standard detectors. Development of new radiometers incorporating superconducting technology and high-T_c materials is an important component of the cryogenic radiometry program. These devices are intercompared to ensure their equivalence in measuring optical power. The Division has been contracted to design, build, and calibrate cryogenic radiometers for NASA's Earth Observing System (EOS) mission and for DoD's BMDO.

• Detector-Based Radiometry. Detector-based radiometry refers to calibration methods that derive from standard detectors rather than standard sources. Chains of comparisons — detector to detector —link customer devices to the cryogenic radiometers. The Division develops transfer-standard detectors to enable high-accuracy radiometric scales, which can be propagated to other laboratories. Transfer standards are being developed at near-infrared and ultraviolet wavelengths that will substantially improve the calibration uncertainties in these areas.

  As an adjunct to the detector program, the Division also develops the specialized capability to precisely measure the area of optical apertures. The uncertainties of the area of apertures are often the limiting factors in radiometric and photometric measurement. The Division is currently applying its expertise to pilot an international comparison of aperture area metrology, under the auspices of the Consultative Committee on Photometry and Radiometry (CCPR).

• Spectral Irradiance and Radiance Calibrations with Uniform Sources (SIRCUS). A reference calibration facility has been developed to transfer detector-based spectral irradiance scales, derived from the HACR, to a number of sensor types including broadband-filtered-detector packages, transfer-standard spectral irradiance detectors, and instruments that measure spectral radiance. This facility will be used to realize NIST's illuminance, luminous intensity, radiance temperature, color temperature, and spectral radiance scales while improving their uncertainties and self-consistency.

  Stabilized, tunable lasers and different-sized integrating spheres are used to create a high-intensity monochromatic source with flexible geometry. It can function as a point source or as a uniform, large-area Lambertian source. The Lambertian sources are calibrated against the standard irradiance meters, traceable to the HACR. Standards-quality radiance meters, calibrated using the Lambertian sources, provide the spectral radiance response scale. The point-source geometry and the inverse-square law are utilized to further minimize the luminous intensity scale uncertainty.

  High performance, transfer- and working-standard radiometers are being developed for spectral irradiance calibrations in the UV, visible, NIR, and IR spectral ranges.

• Source-Based Radiometry. NIST is unique among national laboratories in that the scope of a single Division covers both radiation thermometry and radiometric measurement. This promotes cross-disciplinary research that benefits both fields. There are three known physical principles that relate radiance to fundamental physics: Planck's equation of black body (thermal) radiation, Schwinger's equation of synchrotron radiation (traditionally utilized in the ultraviolet), and a novel stimulated emission, correlated photon technique for determining absolute radiance. By having experimental facilities for all of these mechanisms within the same organization, we are uniquely positioned to intercompare measurement scales based on different principles. The Division also promotes improvement of spectral radiance and radiance temperature scales through detector-based methods, such as those described in the previous section.

• Photometry. Photometry, the science of measuring light with the response function of an "average" human observer, is an integral part of the detector metrology program. The SI base unit for photometry is the candela, a measure of luminous intensity. The Division maintains the unit using a set of well-characterized, filtered detectors which are traceable for their calibration to the HACR.

  Luminous intensity is a property of light sources, such as lamps, and traceability is traditionally through the issuance of calibrated standard lamps. However, the detector method utilized by the Division allows us to offer customer calibrations of photometric detectors, as well as the traditionally used lamps. Additionally, these detector-based methods allow superior calibrations of illuminance (lux), total luminous flux (lumens), and other photometric measurables. These are the quantities most widely used in the lighting and electronic imaging industries.

• Colorimetry and Appearance. Physical measurements of an object's interaction with or emission of light are used by many industries to characterize their products’ color and appearance (gloss, haze, texture, etc.). The primary goals of the NIST program are to develop reference instruments and standards for appearance measurement and to develop new measurements and standards to more accurately capture visual appearance. This work is coordinated with other NIST Laboratories as part of a joint competence-building project that seeks to relate measured appearance (light scattering) properties with surface microstructure, coating formulations, and advanced photo-realistic computer graphic techniques.

  In colorimetry, a new reference high-precision instrument for reflectance color is being assembled. This instrument will eventually be used to implement a measurement assurance program with industry-standard color tiles. Additional projects are developing color-measurement standards for self-luminous objects such as LEDs and display devices.

  For appearance attributes, a new reference goniophotometer is operational, as described under Calibration Services, above. Comparisons of the resultant gloss standards with other national metrology institutes are underway.

• Optical Properties of Materials. A consortium for the measurement of optical properties of materials has been established to provide a link between NIST and the needs of industry. Currently the consortium consists of seven industrial members and has the involvement of three NIST divisions.

  Three Fourier-transform spectrometers are in service with specialized instrumentation to measure the optical properties of materials in the infrared. Measurements of the reflectance (specular and diffuse), transmittance, and refractive index of materials are being performed to customers’ requests in the wavelength range from 1 µm to 1000 µm. These instruments complement the existing spectrophotometers used for calibrations in the UV and visible spectral regions. Capabilities are being developed for variation and control of the critical measurement parameters: temperature, angle of incidence, polarization state, and spot size (IR microscope) to satisfy customers needs.

• Environmental and Remote Sensing. The Division works with DoD, NASA, NOAA, EPA, and other U.S. and foreign government agencies in support of a wide range of space-based and terrestrial measurement programs. These programs involve long-term monitoring and survey activity, which require consistent calibration of instruments with diverse deployment platforms. In addition to actual calibrations, NIST participates in round-robin calibration efforts among the instrument manufacturers and provides cross-calibration with other national laboratories involved in similar activities. Transfer radiometers from the ultraviolet to the far infrared have been built and deployed successfully. The LBIR facility is a key asset in this program. Several portable, stable, and in some cases absolute sources have been designed and built. The Division is involved in developing a radiometer to measure the earth's absolute irradiance for the Triana project. A UV-B monitoring station at Gaithersburg is operated and maintained by the Division.

• Polarized Light Scattering. Mechanisms by which material properties and surface topography affect the distribution and polarization of light scattered from surfaces are studied to develop sophisticated measurement methods for use in industry, e.g., semiconductor, optical, and storage media fabrication. A technique has been developed, called bidirectional ellipsometry, which allows different sources of scattering to be distinguished from one another. A multidetector hemispherical polarized optical scatter instrument has been designed and constructed to perform as a working prototype of a scanning instrument that could be used for silicon wafer inspection. The design was based upon knowledge acquired by bidirectional ellipsometry measurements with a previously constructed goniometric instrument and upon extensive theoretical calculations and simulations. By polarization discrimination, this instrument can be blind to surface microroughness, thereby increasing its sensitivity to particulate contamination or subsurface defects. Pattern recognition techniques are being investigated to enable the instrument to adaptively learn to identify defects associated with an actual production environment. The use of polarized light scattering is enhanced by our introduction of a suite of user-friendly and customizable computer programs titled "SCATMECH: Polarized Light Scattering C++ Class Library," available on the NIST website, that has been downloaded by scores of users.

• Nonlinear Spectroscopy at Interfaces. The nonlinear spectroscopic technique of Sum-Frequency Generation (SFG) is uniquely sensitive to molecular structure at interfaces. Our new implementation of SFG relies on femtosecond lasers and nonlinear optics to generate ultra-fast, spectrally-broad, IR pulses. These are mixed at the interface of interest with transform-limited picosecond visible pulses so that the entire SFG spectrum in the IR region of interest is produced and recorded on every laser shot, rapidly obtaining vibrationally-resonant, SFG spectra with high resolution and signal-to-noise.

  Current measurement applications include semiconductors (structure of thin gate dielectric layers of silicon dioxide on silicon), biomimetic membranes in water used for bio-sensors, and liquid crystal/polymer interfaces used in optoelectronics. This research is joint with the Surface and Microanalysis Science Division and Biotechnology Division in the Chemical Sciences and Technology Laboratory, and the Polymers Division in the Materials Science and Engineering Laboratory.

• Terahertz Spectroscopy of Biomolecules. An effort in Terahertz (THz) technology, supported by the Director's Competence Program, is increasing the Division's expertise in long-wavelength, 60 µm to 3 mm (0.1 THz to 5 THz), pulsed and continuous-wave (cw) coherent laser spectroscopy and imaging. The technology is being applied to model biomolecules to understand the complex dynamics involved in such processes as molecular recognition and protein folding, and includes supplementary studies at microwave, infrared, and ultraviolet frequencies.

  The Terahertz competence project includes joint research with the Center for Neutron Research (Materials Science and Engineering Laboratory) to utilize complementary tools to study dynamical processes of proteins and DNA. We are comparing state-of-the-art pulsed and cw THz optical measurements to high-resolution neutron scattering data to explore the microscopic, concerted, nuclear motions associated with molecular conformational changes. Determining the time-dependent variation in torsional motions and biomolecular interactions is crucial for understanding the biological function of enzymes, protein-drug interactions, and DNA helix transitions at a molecular level. We expect to include molecular mechanics vibrational-torsional frequency calculations to aid in the interpretation and understanding of the observed spectral measurements.