CARS imaging allowed by Four-Wave-Mixing widely tunable by chirped pulses

Fiber-based light sources with a tunability range well beyond the gain bandwidth allowed by the available doped-fiber media are highly demanded for numerous applications including biomedical nonlinear imaging. For instance, coherent Raman microscopy requires the combination of at least two beams at two different wavelengths with one of them spectrally tunable, to explore the resonances of the different molecules in the sample [1]. Nonlinear frequency conversion based on four-wave-mixing (FWM) in microstructure fibers offers a flexible tool allowing to obtain wide wavelength tunability, with impressive performances [2]–[4]. To date, such a spectral tunability has been enabled exclusively by tuning the pump wavelength. Here, we demonstrate that an analogous effect and with a comparable spectral range can be obtain also by stretching an ultrashort pulsed pump at fixed wavelength.