Multi-photon microscopy (MPM) has become an indispensable tool for observing biological structures and functions in vivo, benefitting from its deep penetration depth and high spatial resolution. Femtosecond pulses featuring a broad wavelength tuning range are highly desired by MPM. We demonstrate a 1-MHz ultrafast fiber-optic source that produces ~100-fs pulses tunable from 940 nm to 1250 nm with 100-nJ level pulse energy. For example, we achieved 120-fs pulses with 105-nJ energy centered at 1150 nm. This broadly tunable, energetic fs source constitutes an ideal source for deep-tissue multi-photon imaging.
We demonstrate label-free multimodal multiphoton microscopy in human skin tissue with an ultrafast Er:fiber-laserbased source that emits femtosecond pulses at 775 nm and 1250 nm. This novel two-color fiber-based source enables second-harmonic generation, third-harmonic generation, and two-photon excitation fluorescence, which serves as a potential solution to optical virtual skin biopsy with compactness, robustness, and cost-effectiveness.