- Calibration Services. The Division provides calibration
services and measurements in the areas of 1) radiance temperature,
2) photometry, 3) spectroradiometric sources,
4) spectroradiometric detectors, and 5) optical properties of
materials. During the past year, new calibration services were established for
the photometry of flashing lights. The initial customers are in the aviation
industry, since these services enable airlines to adhere to FAA safety
standards. An improved calibration facility for luminous flux was also
inaugurated. The Division has an ambitious program to maintain and improve the
quality of its calibration services. Having completed implementation of ISO
Guide 25 in all of our services, we are currently studying the future
requirements and impact of ISO 17025.
- Training. The Division offers short courses in photometry and
radiation thermometry. It plans to initiate a short course in spectroradiometry,
covering both sources and detectors.
- Cryogenic Radiometry. The Division utilizes and advances the
technique of cryogenic radiometry to relate optical power to the SI watt. Within much of the
optical spectrum and at most power levels, cryogenic radiometry yields the
lowest measurement uncertainties among current technologies.
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 to improve utility, sensitivity, and accuracy.
A high-sensitivity cryogenic radiometer is the 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 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-Tc materials is an important component of the cryogenic
radiometry program. 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 is a strength
of the Division. This refers to calibration methods that derive from standard
detectors rather than standard sources, which are neither as stable, nor as
rugged. 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 to 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.
- 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.
- 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 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 method utilized by the Division allows us to offer customer
calibrations of photometric detectors as well, which provide superior results.
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 light (spectral reflectance, scattering pattern, etc.) and
emission of light are used by industry to characterize the object’s color and
appearance (gloss, haze, texture, etc.). The primary goals of the program are
development of reference instruments and standards for current
appearance-measurement technologies, and eventual development of new
measurements and standards to more accurately capture visual appearance.
The Division has recently completed initial development of a new reference
goniophotometer. It was developed for the characterization of specular gloss at
the 20º, 60º, and 85º geometries that are required by important ASTM and ISO
standards. A new specular gloss primary standard has been issued. 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 the area of colorimetry, the Spectral Tri-function Automated Reference
Reflectometer (STARR) is being used to develop a measurement assurance program
with industry standard color tiles and to perform research into the instrument
attributes necessary for accurate colorimetry for future calibration services.
Additional projects are developing color-measurement standards for
self-luminous objects such as LEDs
and display devices.
- Spectrophotometry. A consortium for 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 involves 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 reflectance (specular and diffuse), transmittance, refractive
index of materials are being performed to customers’ specifications in the
wavelength range from 1 µm to 1000 µm. Capabilities are
being developed for variation and control of the critical parameters:
temperature, angle of incidence, polarization state, and spot size (IR
microscope) for these measurements to satisfy customer’s needs.
- Environmental and Remote Sensing. The Division works with 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.
Several portable, stable, and in some cases absolute sources have been designed
and built. An international round robin on bi-directional reflectance
distribution function was recently completed.
- Polarized Light Scattering. By analyzing the polarization state of
polarized light scattered from a surface, as a function of scattering angle,
one can distinguish surface microroughness, subsurface defects, and particulate
contamination. This new technique, called bidirectional ellipsometry, is being
applied to the needs of the semiconductor, optical component, and data-storage
media industries.
Mechanisms by which material properties and surface topography affect the
distribution and polarization of scattered light are studied to develop
innovative measurement methods. 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. Pattern recognition techniques are being investigated to enable the
instrument to adaptively learn to identify defects associated with an actual
production environment.
- Near-field Scanning Optical Microscopy (NSOM). NSOM is being
developed as a quantitative technique for noninvasive, optical measurements.
Its resolution is not limited by the wavelength of light, as in traditional
diffraction-limited microscopy, but by the size of the sub-wavelength aperture
or tip used as a probe. Well-characterized microscopes and compact light
sources have been constructed, and methods to determine resolution are being
developed. This requires a fundamental understanding of contrast mechanisms and
modeling the fields around small light sources as they interact with materials
and surface features. The Division collaborates with other NIST programs
applying near-field microscopy to problems in chemical, biological, optical,
and semiconductor technology.
- Nonlinear Spectroscopy at Interfaces. The nonlinear spectroscopy 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 (the 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.
- Analytic Spectroscopy. Spectroscopic technology is increasingly
important for applications in chemical analysis and detection, including
atmospheric remote sensing, emissions monitoring, catalysis, industrial process
control, forensic science, medical diagnostics, chemical manufacturing, and
materials development. The Division has a vertically-integrated research and
development effort to support this technology. The effort includes:
(1) establishing and disseminating spectroscopic data to facilitate
choices of monitoring frequencies and inversion of measurements to extract
concentrations, (2) developing quantum-mechanical Hamiltonians that
provide convenient and concise representations of spectroscopic data and their
validation, (3) making laboratory spectroscopic measurements to provide
accurate frequency and intensity information for instrument calibration,
(4) developing of new optical chemical-sensor technology in the microwave,
infrared, and visible/UV spectral regions, (5) working with other
government agencies to solve novel and important chemical-analysis and
detection problems, and (6) working with industry to transfer these
technologies and to assess needs for new optical chemical analysis technologies,
standards, and data.
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