Practical realization of the watt from Planck’s constant using radiation pressure

A primary force standard is implemented to realize the watt through Planck's constant by means of radiation pressure at the kilowatt level. The high amplification laser-pressure optic, or HALO, is a multiple reflection radiation pressure apparatus used for absolute radiometry of high-power lasers. In this work, a primary standard electrostatic force balance is used to measure the reflection-enhanced optical forces. With this configuration, the HALO is used to measure laser powers in the range of 100 W-5000 W from a 1070 nm fiber laser. The expanded uncertainty of the 5 kW measurement is 0.12%, which is both the lowest uncertainty multi-kW measurement and radiation pressure-based measurement to-date. The HALO result was validated against a thermal primary standard using a calibrated transfer standard at 2 kW. The degree of equivalence was 0.78% ± 1.12%, which demonstrates agreement within the uncertainties of these two primary standards.