Bilateral comparison of power measurement standards for KrF excimer lasers between PTB and NIST

We report results of the first bilateral laser power comparison for 248 nm KrF excimer lasers accomplished by the National Metrology Institutes of Germany (Physikalisch-Technische Bundesanstalt, PTB) and of the United States of America (National Institute of Standards and Technology, NIST). Laser transfer standards for average power were calibrated at both laboratories. The average powers were approximately 0.5 W, 1 W and 2 W. At 248 nm, the relative agreement was between 1×10−3 and 6×10−3, which is well within the expanded uncertainty of the bilateral degree of equivalence of approximately 2×10−2. Thus, this comparison confirms that the measurement procedures of both laboratories are consistent and the uncertainty budgets contain all significant contributions.