Figure 1.

(A) Transition dipole moment (TDM) of each molecule is tilted at an angle φ from the membrane normal and an angle ψ around it. The intensity of fluorescence or SHG from the ensemble of dyes is dependent on the angle away from the laser polarization, θ. (B) Variation of SHG from di-4-ANEPPS, which varies periodically with θ around the equator of a model membrane (giant unilamellar vesicle). The shape of this curve, when fit to a model, allows extraction of trigonometric moments of the tilt distribution, P_tilt(φ). The direction of laser excitation is co-linear with the direction of signal detection and perpendicular to the plane of the image in panel B.