Sphere-Wall Impact Experiments with Piezoelectric Force Sensors

Measurement of impulse imparted to a target from μs‐timescale laser ablation events is often performed with piezoelectric force sensors. For pulsed laser ablation with a target resting on the force sensors, an effect can occur for a vertical thrust stand in an exhaust‐up configuration that results in measurement of about twice the actual imparted impulse. A CO2 laser operating at 10.6 μm wavelength, 300 ns pulse length, and up to 20 J pulse energy single shots was used to ablate samples of PCTFE. Force sensor measurements of the imparted impulse were compared to tests with a ballistic pendulum over a variety of fluences. The theoretical impulse delivered by the impacts of 6 mm diameter spheres of aluminum, steel, POM, and PTFE on the force sensor were studied, and the coefficients of restitution were measured for the targets. Practical issues for measurement of ablation‐imparted impulse with piezoelectric sensors are discussed.