Figure 2.13 — Optical traps with non-uniform beams Figure 2.13 — Optical traps with non-uniform beams. Trapping efficiencies in the longitudinal (top) and transverse (bottom) planes for a Gaussian beam with waist equal to (a) 30% and (b) 70% of the objective pupil aperture, and (c) for an annular beam. We consider the trapping of a glass (radius a = 3 μm, np = 1.50) sphere immersed in water (nm = 1.33). The beam profile on the water-immersion objective (NA=1.20) entrance pupil is shown on the top.