High accuracy measurement of the quantum efficiency using radiation pressure

Preliminary investigations of a novel method to measure the laser power accurately using the radiation pressure are reported here. We aim to measure the laser power within one percent error to then obtain an accurate quantum efficiency (QE) of a photodiode. Since the typical error of QE is still a few percent due to the uncertainty of measured laser power, an accurate measurement of the laser power contributes a precise estimation of the QE. Our experimental setup is a suspended Michelson interferometer, where one of the pendulums is small, consisting of a 20-mg mirror and 10-um fiber. The motion of this small mirror is very sensitive to changes in radiation pressure. Due to this, the number of photons in the incident (intensity modulated) laser beam can be counted accurately by measuring displacement of the mirror. We set up the apparatus, and have found a suitable frequency band for the accurate measurement. Displacement caused by the radiation pressure was observed using the feedback signal.