A detector-based spectral irradiance scale has been realized at the National Institute of Standards and Technology (NIST). Unlike the previous NIST spectral irradiance scales, the new scale is generated with filter radiometers calibrated for absolute spectral power responsivity traceable to the NIST high-accuracy cryogenic radiometer instead of with the gold freezing-point blackbody. The calibrated filter radiometers are then used to establish the radiance temperature of a high-temperature blackbody (HTBB) operating near 3,000 K The spectral irradiance of the HTBB is then determined with knowledge of the geometric factors and is used to assign the spectral irradiances of a group of 1,000-W free-electron laser lamps. The detector-based spectral irradiance scale results in the reduction of the uncertainties from the previous source-based spectral irradiance scale by at least a factor of 2 in the ultraviolet and visible wavelength regions. The new detector-based spectral irradiance scale also leads to a reduction in the uncertainties in the shortwave infrared wavelength region by at least a factor of 2-10, depending on the wavelength. Following the establishment of the spectral irradiance scale in the early 1960s, the detector-based spectral irradiance scale represents a fundamental change in the way that the NIST spectral irradiance scale is realized.

A new reflectometer-spectrophotometer has been designed and constructed using state-of-the-art technology to enhance optical properties of materials measurements over the ultraviolet, visible, and near-infrared (UV-Vis-NIR) wavelength range (200 nm to 2500 nm). The instrument, Spectral Tri-function Automated Reference Reflectometer (STARR), is capable of measuring specular and diffuse reflectance, bidirectional reflectance distribution function (BRDF) of diffuse samples, and both diffuse and non-diffuse transmittance. Samples up to 30 cm by 30 cm can be measured. The instrument and its characterization are described.

This document describes the instrumentation, standards, and techniques used at the National Institute of Standards and Technology to measure spectral reflectance over the ultraviolet, visible, and near infrared wavelength ranges. The organization is as follows. Part I describes the motivation for maintaining reference and transfer spectrophotometers for spectral reflectance measurements, the basics of reflection, and the standards and services that are available from NIST. Part II develops the necessary theory of reflection, beginning with basic definitions and equations and ending with the relevant measurement equations for the experiments described in this documentation. The NIST Spectral Tri-function Automated Reference Reflectometer is described in Part III. This instrument provides the basis for the development of absolute NIST standards of diffuse and specular reflectance. Part IV describes the NIST transfer spectrophotometers, high precision commercial instruments used for calibrating Standard Reference Materials such as diffuse reflectance and specular reflectance standards. The transfer instruments rely on master standards that are periodically calibrated on the high accuracy reference reflectometer described in Part III. References containing details are reproduced in the appendices.

No abstract