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Accurate measurements of the optical properties
of materials in the infrared spectral range play an increasingly
important role in the aerospace and defense industries, optical
engineering, condensed matter physics, remote sensing, radiative
heat transfer measurements and related areas. The laboratory for
infrared optical properties measurements has established high
accuracy infrared reflectance and transmittance capabilities for
wavelengths between 1 µm and 18 µm. Near normal absolute
spectral reflectance and transmittance of both specular and diffuse
samples can be measured from near ambient to 200 °C using a
custom integrating sphere and Fourier transform (FT) spectrometer.
Additional capabilities for specular samples include transmittance
down to 10 K using an optical cryostat, as well as variable angle
transmittance and reflectance using a custom goniometer and
polarizers. Special test measurements are performed for both NIST and
external customers in government and industry on a wide variety of
materials including mirrors, filters, windows, coatings and cavity
structures. Emittance and absorptance are obtained indirectly through
combining the reflectance and transmittance under identical
conditions. Also, a newly developed facility is available for the
measurement of directional spectral emittance for sample temperature
up to 1000 °C, accomplished through comparison of radiance with
reference blackbody sources. This new facility supplements and
extends the overall optical properties effort to be more
comprehensive in meeting the customers' needs and providing the
highest accuracy data.
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Infrared Spectrophotometry
Infrared Laser Gonioreflectometer Instrument (ILGRI)
Complete Hemispherical Infrared Laser-based Reflectometer (CHILR)
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Our Approach to Optical Property
Measurements
Develop comprehensive measurement capability for
the infrared spectral region
- Wide range of optical properties
- Wide range of material types (specular & diffuse,
transmissive & opaque)
- Cover range of critical parameters (temperature, beam geometry
& polarization state)
Evaluate and develop measurement methodologies for high accuracy
- Direct method for absolute hemispherical reflectance
- Use integrating sphere for specular samples
- Develop Monte Carlo techniques for analysis and optimization
of instrument
Investigate and understand major sources of
measurement error
- Fourier Transform Spectrometry (hardware and software)
- Detector spatial uniformity and linearity
- Compare direct and indirect emittance and reflectance
Develop, design and implement custom accessory instrumentation
Intercompare with other techniques and other Laboratories
- Compare FT with laser and monochromotor measurements
- Internal with UV-vis-NIR reference instruments
- External with National Metrological Institutes
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Capabilities
- Spectral Regular Transmittance,
λ = 1 µm to 100 µm
- Spectral Specular Reflectance (opaque
and transparent samples),
- normal incidence
λ = 1 µm to 18 µm
- variable angle (10° to 80°)
λ = 1 µm to 5 µm (to
25 µm)
- Spectral Directional-Hemispherical
Reflectance and Transmittance (diffuse samples),
λ = 290 K to 475 K
- Spectral Absorptance and Emittance,
Indirect Measurements (1 - R - T),
from above capabilities (specular and diffuse samples)
- Spectral Emittance, Direct measurements,
λ = 1 µm to 20 µm,
575 K to 1275 K
- Spectral Refractive Index,
λ = 0.5 µm to 20 µm
- Laser-based Bi-directional Reflectance and
Transmittance Distribution Function (BRDF and BTDF) and
Total Integrated Scatter (TIS)
- Polarimetry
- Ellipsometry

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