Deep-tissue two-photon brain imaging enabled by a tunable fiber-optic dispersive wave generator

Here, we present a fiber-optic dispersive wave generator for highly-efficient, wavelength-tunable ultrashort pulse generation, enabling multicolor deep-tissue two-photon imaging of neuronal and vascular structures in fixed, labeled mouse brain. Guided by comprehensive numerical simulations, a compact Yb: fiber laser-driven system is constructed that utilizes precisely parameter- and phase-matching-controlled dispersive wave generation in a photonic crystal fiber. The system delivers sub-100 fs pulses with over ~ 6.7 nJ of energy across a continuously tunable spectral range of 880-950 nm, achieving a record-high optical conversion efficiency of up to 65%. Optimizing the output for two-photon excitation of enhanced Green Fluorescent Protein and SYTOX Orange enables high-resolution structural imaging in mouse hippocampus and cerebellum at depths exceeding 450 μm. This technique for wavelength-tunable, high-energy and ultrashort pulse generation with record optical efficiency represents a significant advancement in ultrafast fiber laser technology for versatile biomedical two-photon imaging applications.