Figure 2.
TIR from multiple directions. (A) Eight 2D plane waves in the evanescent field converging to an in-phase center. (B) An infinite number of such 2D plane waves, creating a converging circular wave. (C) This circular converging pattern can be produced by a thin annulus of illumination at the BFP of the microscope objective used for TIRF excitation. The polarization at the BFP must be radial so that all of the evanescent fields from each plane wave component will be predominantly in the z direction (normal to the TIR surface) and thus will mutually interfere. (D) The evanescent intensity theoretically predicted from such annular illumination according to Eq. 5. The width of the central maximum to the first minimum is ∼0.26 λo, assuming the annular ring at the BFP has a radius corresponding to NA = 1.45, which is easily accessible with a 1.49 NA objective.