Logo der Physikalisch-Technischen Bundesanstalt

A bilateral comparison of NIST and PTB laser power standards for scale realization confidence by gravitational wave observatories


The gravitational wave (GW) observatories calibrate interferometer displacement using photon momentum, with laser power serving as the measurand. These observatories are traceable to the International System of Units through a primary standard maintained by the US’s National Metrology Institute (NMI), the National Institute of Standards and Technology (NIST). The bilateral degree of equivalence of laser power measurements for various NMIs indicated in the 2010 EUROMET.PR-S2 supplementary comparison reveals scale realization uncertainty unacceptably large for GW event parameterization. We offer here an analysis to identify the source of the discrepancy between the Physikalisch-Technische Bundesanstalt (PTB) and NIST results. Using an improved transfer standard in a bilateral comparison, with representatives of the Laser Interferometer Gravitational-Wave Observatory (LIGO) receiving results prior to their comparison, NIST and PTB demonstrated a degree of equivalence of −0.15% with an uncertainty of 0.95% (k = 2) for combined 100 mW and 300 mW comparison results.


Absolute responsivity of the transfer standard as evaluated at NIST and PTB using powers of 100 mW (a) and 300 mW (b) at 1047 nm.

Matthew Spidell, National Institute of Standards and Technology, Boulder, Colorado, United States of America
 John Lehman, National Institute of Standards and Technology, Boulder, Colorado, United States of America
Marco Lopez, Physikalisch-Technische Bundesanstalt, Braunschweig, Germany
Holger Lecher, Physikalisch-Technische Bundesanstalt, Braunschweig, Germany
Stefan Kück, Physikalisch-Technische Bundesanstalt, Braunschweig, Germany
Dripta Bhattacharjee, LIGO Hanford Observatory, Richland, Washington, United States of America


Leiter der Presse- und Öffentlichkeitsarbeit

Dr. Dr. Jens Simon

Telefon: (0531) 592-3005


Physikalisch-Technische Bundesanstalt
Bundesallee 100
38116 Braunschweig