IMPROVED MEASUREMENT SYSTEM FOR INFRARED PROPERTIES OF MATERIALS.

NIST has a new instrument to provide enhanced characterization of infrared optical properties of materials. The instrument is currently being used to calibrate gold mirrors for use as reference standards by a manufacturer of reflectance and scattering distribution measurement systems. This work is being done under the auspices of the Optical Properties of Materials Consortium. The Consortium is geared for partners interested in the development of standard reference materials and calibration services to characterize optical properties such as transmittance, reflectance, emittance, and polarization over the wavelength regions of UV to far IR.

The instrument uses a precision goniometer and has a Fourier-transform infrared (FTIR) spectrophotometer as a source. The system can measure variable angle absolute reflectance and transmittance from 12[degrees] (and 0[degrees]) to [greater than]80[degrees], over the 1 [micro]m to 5[micro]m wavelength range with an expanded (k = 2) uncertainty of 0.002. Improvements to the new measurement system are underway: the wavelength range will be expanded to 20 [micro]m and IR ellipsometry measurement capability will be established. These improvements are expected to improve the accuracy in the determination of IR optical constants of opaque materials.