Power measurement standards for high-power lasers: comparison between the NIST and the PTB

We report the results of the first laser high-power measurement comparison between the Physikalisch-Technische Bundesanstalt (PTB, Germany), and the N ational Institute of Standards and Technology (NIST, USA). Laser power tran sfer standards were calibrated at both national standards laboratories betw een 82 W and 127 W at 1.06 mum and between 85 W and 554 W at 10.6 mum. Rela tive agreement between the standards of the two laboratories was demonstrat ed to lie between 5 x 10(-3) and 7 x 10(-3), which is well within the combi ned uncertainties.