Quasi white light multiphoton imaging

We describe the realization and characterization of a broadband, high power density and fully spectrally controllable source, suitable for multiphoton imaging of biological samples. We used a photonic crystal fiber (PCF) with selected dispersive and non-linear properties, in order to generate, when pumped with <140 femtosecond pulses delivered by a tunable Ti:Sa laser (Chameleon Ultra II by Coherent Inc.), a smooth continuum in the 700nm-950nm region, with average power density grater than 2mW/nm. Time distribution of the generated spectrum has been measured with autocorrelation technique. Axial and lateral resolution obtained with a scanning multiphoton system has been determined to be near the theoretical limit. The possibility of two-photon excitation of different dyes in the same sample and high image resolution are demonstrated at tens of microns in depth. Future developments and different applications are also discussed.