Tricolor synchronized ultrafast fiber laser for coherent anti-Stokes Raman scattering imaging

Coherent anti-Stokes Raman scattering (CARS) microscopy requires synchronized excitation pulses with sufficient peak power, and broad pump-Stokes frequency coverage. We demonstrate a tricolor synchronized ultrafast fiber laser derived from a common 1.55 μm mode-locked Er-fiber oscillator. The master branch is frequency doubled to generate a 775 nm picosecond pulse train for fingerprint-region CARS. A second branch produces a 1063 nm picosecond pulse train through cross-phase-modulation-synchronized mode locking in a Yb-fiber oscillator, followed by fiber amplification and compression. A third branch combines large-mode-area Er/Yb Raman amplification with soliton self-frequency shift to generate high-energy femtosecond pulses at 1600-1840 nm, which are subsequently frequency doubled to provide tunable 805-920 nm femtosecond pulses. The system delivers approximately 150 mW at 775 nm, more than 1 W at 1063 nm, 1.6 W at 1840 nm with a pulse energy of 29.57 nJ, and up to 362 mW in the 805-920 nm band. The 775 nm and 805-920 nm pulse pair cover Raman shifts of approximately 480-2033 cm -1 , while the 805-920 nm and 1063 nm pulse pair cover approximately 1462-3015 cm -1 . CARS spectroscopy and imaging of ethanol, dimethyl sulfoxide, polystyrene microplastic particles, avocado pulp, onion cells, and human stratum corneum verify chemically selective imaging in both the fingerprint and high-wavenumber regions. The proposed architecture provides a compact fiber-dominant synchronized source for broadband CARS microscopy.