Fig. 4.

Normalized scattered intensity profiles as a function of height for a 3-μm diameter SiO₂ bead in water as angle of incidence of probe beam is varied. Fitted decay lengths of the evanescent field intensity are 90.8 nm, 110.6 nm, 115.6 nm, 159.9 nm, 185.2 nm, 236.4 nm, and 268.9 nm, corresponding to angles of 68.6°, 65.9°, 63.4°, 63.3°, 62.7°, 62.1°, and 61.8°, respectively. The error on all fits is less than 1%. The critical angle is 61.0° for the system. For clarity, raw data are shown for the longest and shortest decay length measurements. Inset plots color-coded decay lengths (as measured) on the curve ${\beta }^{-1}\left(\theta \right)$.