Fig. 1.

Schematic of the polarization-dependent effects in 2P LSM, assuming a fixed orientation of the fluorophore dipole moment. (a) If both the polarization plane (indicated by short red arrows) of the linearly-polarized excitation light (red arrow) and the transition dipole of the fluorophore (black line) are aligned with the z-axis, the fluorophore is excited, but the fluorescence light (colored distribution) is emitted predominately on the xy-plane [24]. (b) If the polarization plane of the excitation light is parallel to the y-axis while the transition dipole is perpendicular to it, then no fluorescence light is generated. (c) If both the polarization plane of the excitation light and the transition dipole are aligned with the y-axis, then the fluorescence light is emitted predominately on the xz-plane and therefore part of it (green arrow) can be collected by the detection objective (on the z-axis).