Philip H. Jones, Onofrio M. Maragò & Giovanni Volpe
Fig. 10.2 — Photonic force microscope
An optical tweezers produces a force field that is harmonic, so that an optically trapped particle experiences an elastic restoring force with stiffness κx (force field on the left). As a uniform force Fext,x acts on the optically trapped particle (force field in the centre), it displaces the particle probability distribution by Δx, so that one can measure Fext,x = κx Δx (force field on the right).