Figure 1. Schematic diagram of the optical setup.

A wide-field yellow excitation laser beam is shuttered by an acousto-optical modulator, focused onto the back aperture of an Olympus TIRF objective, which collimates the laser light at an inclined angle. A violet photoconversion laser beam is shuttered by a mechanical shutter, and is spatially overlapped with wide-field yellow imaging beam. An anamorphic prism pair (06 GPA 204, Melles Griot) corrects for asymmetry of this laser beam to produce a TEM₀₀ mode.