Pulsed femtosecond laser (2PE) provides two-photon excitation to the sample (red), and fluorescence (green) is collected and imaged onto a camera. The remaining elements are used to shape, modulate, shutter, or scan the excitation, or scan and filter the emission (see text for more detail). Symbol key: HWP, half wave plate; POL, polarizer; EXC 2D GALVO, galvanometric mirror used to scan the excitation through the sample; DC, dichroic mirror; IX-70, microscope frame used to house the objective and sample (not shown); EM 2D GALVO, galvanometric mirror used to rescan the emission. Reflective mirrors are shown as rectangles, and other lenses referred to in the text are shown as ellipsoids with focal lengths as indicated. Note that the drawing is not to scale.