Fig. 10.4 — Photonic force microscope in a rotationally symmetric potential

(a)–(c) Photonic torque microscope with a rotationally symmetric harmonic potential, i.e., κ_x = κ_y or, equivalently, 􏰀κ = 0, for various values of Ω. The shaded areas show the probability distribution function of the probe particle position in the corresponding force field (arrows). When Ω = 0, the probe movement can be separated along two orthogonal directions. When the (absolute) value of 􏰁 increases, the force field lines bend and the probe movements along the x– and y-directions are not independent any more. (d)-(f ) Corresponding autocorrelation functions C_x(τ) (black solid line) and cross-correlation functions C_xy(τ)(grey solid line) [Eqs. (10.6) and (10.7)]. Note that C_y(τ) = C_x(τ) and C_yx(τ) = C_xy(−τ).