Enhanced Self-Phase Modulation Enables a 700–900 nm Linear Compressible Continuum for Multicolor Two-Photon Microscopy

The spectral band of 100-fs pulses limits its simultaneous and efficient excitation in multicolor two-photon microscopy. By pumping the pulses from the 100-fs Ti:Sapphire oscillator through the highly nonlinear photonic crystal fiber, we demonstrate that a 700-900 nm linear compressible continuum can be generated due to enhanced self-phase modulation. Such a continuum is linearly compressed to 57 fs at the objective focus by a grating pair. The two-photon imaging of three-color labeled bovine pulmonary artery endothelial cells shows that the compressed continuum not only simultaneously excites the three fluorescent dyes, but also enhances the signal over 20 times compared with that of uncompressed case. This study shows its potential to promote the fluorescence signal level by using fiber continuum in multicolor two-photon microscopy.