Figure 4.14 — Optical forces on a dipole Figure 4.14 — Optical forces on a dipole. Forces produced on a dipole particle (np = 1.50) in water (nm = 1.33) near the focus of an x-polarised Gaussian beam with beam waist (a) w0 = 4 mm and (b) w0 = 2 mm, and for (c) a radially polarised and (d) an azimuthally polarised cylindrical vector beam. All beams have wavelength λ0 = 632 nm, have 10 mW power after the aperture and are focused by a 1.20 NA water-immersion objective with aperture radius of 4 mm. The corresponding focal fields are illustrated in Fig. 4.13.