Optical Power Scale Realization by Laser Calorimeter after 45 Years of Operation

• Published in: Journal of research of the National Institute of Standards and Technology Vol. 126; pp. 126011 - 14
• Main Authors: Spidell, Matthew T, Vaskuri, Anna K
• Format: Journal Article
• Language: English
• Published: United States Superintendent of Documents 28.06.2021; [Gaithersburg, MD] : U.S. Dept. of Commerce, National Institute of Standards and Technology
• Subjects: Calibration; Energy; Geometry; Gravitational waves; Heat; Laboratories; Lasers; Optical coupling; Radiant flux; Representations; Thermal analysis; Uncertainty; calorimetry; laser power; primary standard
• ISSN: 1044-677X; 2165-7254; 2165-7254
• DOI: 10.6028/jres.126.011

To calibrate laser power and energy meters, the National Institute of Standards and Technology (NIST) uses several detector-based realizations of the scale for optical radiant flux; these realizations are appropriate for specific laser power/energy ranges and optical coupling configurations. Calibrations from 1 µW to 2 W are currently based upon calorimeters. Validation by comparisons against other primary representations of the optical watt over the last two decades suggests the instruments operate well within their typical reported uncertainty level of 0.86 % with 95 % confidence. The dominant uncertainty contribution in the instrument is attributable to light scattered by the legacy window, which was not previously recognized. The inherent electro-optical inequivalence in the calorimeter's response was reassessed by thermal modeling to be 0.03 %. The principal contributions to the overall inequivalence were corrected, yielding a shift in scale representation under 0.2 % for typical calibrations. With updates in several uncertainty contributions resulting from this reassessment, the resulting combined expanded uncertainty (k = 2) is 0.84 %, which is essentially unchanged from the previous result provided to calibration customers.