Spectrally Tunable Sources for Advanced Radiometric Applications

Current radiometric source standards disseminated by national metrology institutes (NMIs) such as the National Institute of Standards and Technology (NIST) in the United States utilize traditional technologies, e.g., tungsten filament lamps and blackbodies; reflectance plaques and integrating spheres. These standards are spatially uniform and have spectral properties that vary smoothly with wavelength. These are important characteristics with respect to the practical, economic, and consistent dissemination of standards with values that are traceable to the International System of Units (SI) with the lowest possible uncertainties. These sources are ideal for cases where customers' applications utilize sources with similar spectral and spatial properties. However, there are many applications of critical significance where the sources have unique properties. Many types of measurement bias exist in radiometry, and these effects are exacerbated when the calibration and the target source differ in their fundamental influencing parameters such as spectral or spatial distribution, brightness, or temporal behavior. As a consequence, while the existing sources provided by NMIs are important for general calibration applications, they tend to have limited utility for advanced characterization and calibration measurements. The absence of relevant, application-specific, radiometric artifacts to evaluate the performance of instruments, or to provide an application-specific calibration source standard, limits the ability of end users to verify the measurement results, sometimes with adverse consequences. Therefore, the need exists for advanced calibration artifacts to improve measurement