![Fig. 10.2 — Photonic force microscope](https://i0.wp.com/opticaltweezers.org/wp-content/uploads/2015/11/Fig10_2.png?fit=660%2C231)
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).
Fig. 10.2 — Photonic force microscope