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A new instrument is required to accommodate the need for increasedportability and accuracy in laser power measurement above 100 W. Reflection andabsorption of laser light provide a measurable force from photon momentumexchange that is directly proportional to laser power, which can be measuredwith an electrostatic balance traceable to the SI. We aim for a relativeuncertainty of $10^{-3}$ with coverage factor $k=2$. For this purpose, we havedesigned a monolithic parallelogram 4-bar linkage incorporating elasticcircular notch flexure hinges. The design is optimized to address the mainfactors driving force measurement uncertainty from the balance mechanism:corner loading errors, balance stiffness, stress in the flexure hinges,sensitivity to vibration, and sensitivity to thermal gradients. Parasiticrotations in the free end of the 4-bar linkage during arcuate motion areconstrained by machining tolerances. An analytical model shows this affects theforce measurement less than 0.01 percent. Incorporating an inverted pendulumreduces the stiffness of the system without unduly increasing tilt sensitivity.Finite element modeling of the flexures is used to determine the hingeorientation that minimizes stress which is therefore expected to minimizehysteresis. Thermal effects are mitigated using an external enclosure tominimize temperature gradients, although a quantitative analysis of this effectis not carried out. These analyses show the optimized mechanism is expected tocontribute less than $10^{-3}$ relative uncertainty in the final laser powermeasurement.

Design of an electrostatic balance mechanism to measure optical power of 100 kW