Single-period readout self-resetting silk torque sensor

Torsion pendulums offer exceptional torque sensitivity but inherently suffer from slow response times, limiting time-resolved measurements. We present a single-period, self-resetting optical torque sensor based on a silk fiber torsion pendulum operating in ultra-high vacuum. This non-resonant, time-domain approach enables the detection of discrete optical torque pulses at the attonewton-meter level within seconds, without high quality factors or active damping. The pendulum's intrinsic mechanical relaxation provides a natural reset between measurements, allowing successive readings. We validate the method using radiation-pressure torque from a laser beam and demonstrate its practicality by measuring solar radiation pressure, providing a compact platform for dynamic optomechanical force sensing.