We seek to make the most accurate measurements of kilowatt-class (CW) lasers and are using radiation pressure to do so. Currently, the most accurate laser power measurements are performed by measuring heat transferred into a cryogenic radiometer, but at significantly lower power levels (microwatts). This does not easily scale to very high powers. With radiation pressure-based detection, the power in a laser beam is measured from its momentum – the force imparted when a laser beam reflects from a mirror. Since this process changes a light beam’s momentum but does not significantly affect its energy, multiple reflections from a force-sensing mirror can multiply the force without significantly increasing the noise. This presents a promising means to produce a low-uncertainty measurement of kilowatts of laser power. We are testing the uncertainty limits offered by such an approach at kilowatt optical power levels.
We have assembled a high-accuracy laser power meter based on radiation pressure with multiple reflections of the laser on the sensing mirror. A custom electrostatic force balance supports a high-reflectivity sensing mirror upon which a high-power continuous wave laser beam is incident at ~ 45 degrees. Symmetrically placed turning mirrors above the sensing mirror recapture the beam and redirect it back onto the sensing mirror a total of 14 times. Our measurement laser has a 10-kW capacity making possible up to 140 kW of recirculated power. We are testing the performance of this system and particularly identifying and minimizing noise sources as we characterize the geometry of the design to produce optimal uncertainty.