An optical power scale is established at Ulusal Metroloji Enstitü sü (UME) using the helium-cooled primary-level electricalsubstitution cryogenic radiometer. The scale is established at discrete laser wavelengths of vertically polarized tuneable Ar ϩ , fixed He-Ne, and Nd:YAG (with second harmonic) laser sources. To increase measurement accuracy, laser intensities are stabilized to better than 0.009% using an electro-optical modulator. The spatial profiles of polarized laser beams are cleaned with a spatial filter. The optical power is measured using the static substitution method with an uncertainty of a few parts in 10 Ϫ4 . Repeatability of optical power measurements in the static substitution method, the measurement of window transmittance, and the measurement of power in a scattered beam are the most significant uncertainty components.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.