Label-free multimodal nonlinear microscopy enabled by an optical parametric generator.

The progress and performance of nonlinear optical microscopy have been paced by breakthroughs in laser technology. Despite substantial advances, a laser source that delivers high peak power and wavelength tunability while supporting multimodal imaging in an experimentally accessible architecture remains elusive. In this contribution, we present a scheme based on an optical parametric generator (OPG). This system bypasses optical cavities and additional amplification stages, providing tunable radiation spanning over 100 nm near the 1500 nm region. We validate the capabilities of the OPG in both nonlinear spectroscopy and microscopy. Spectroscopic performance is established by acquiring coherent anti-Stokes Raman scattering (CARS) spectra of benchmark solvents, followed by narrowband and broadband CARS microscopy of intact and fresh-frozen rodent tissue specimens. In addition to CARS, this light source can also drive two-photon-mediated processes, enabling label-free multimodal imaging, a capability that we demonstrate by co-registering multiphoton autofluorescence, second-harmonic generation, and CARS from freshly excised rodent tissues. Owing to its simple and modular configuration, this design provides an adaptable and cost-effective platform for applications requiring broadband, tunable femtosecond radiation for multimodal nonlinear optical microscopy.