Figure 2.

The excitation pathway schematic for HILO illumination. Incident (i), reflected (r), and transmitted (t) beams in blue have s- or p-polarization $\left({\hat{e}}_s\text{or}{\hat{e}}_p\right)$ for the transmitted beam. They are parallel or perpendicular to the apparent symmetry axis of the in vivo skeletal muscle fiber. Lab fixed coordinates are of two types, TIRF coordinates (θ,ϕ) relative to (L_x,L_y,L_z) and fiber coordinates (β′,α′) relative to (L_x′,L_y′,L_z′), depicting the orientation of the (photoactivated) emission dipole, ${\hat{\mu }}_e$. Symbol σ is the incidence angle of the exciting beam. To see this figure in color, go online.