Wide field light-sheet microscopy with lens-axicon controlled two-photon Bessel beam illumination

Two-photon excitation can lower phototoxicity and improve penetration depth, but its narrow excitation range restricts its applications in light-sheet microscopy. Here, we propose simple illumination optics, a lens-axicon triplet composed of an axicon and two convex lenses, to generate longer extent Bessel beams. This unit can stretch the beam full width at half maximum of 600–1000 μm with less than a 4-μm waist when using a 10× illumination lens. A two-photon excitation digital scanned light-sheet microscope possessing this range of field of view and ~2–3-μm axial resolution is constructed and used to analyze the cellular dynamics over the whole body of medaka fish. We demonstrate long-term time-lapse observations over several days and high-speed recording with ~3 mm(3) volume per 4 s of the embryos. Our system is minimal and suppresses laser power loss, which can broaden applications of two-photon excitation in light-sheet microscopy.