CARS microscopy using linearly chirped ultrafast laser pulses

We have developed a home-built CARS microscope which exploits linearly-chirped ultrafast laser pulses. By using glass of high group-velocity dispersion, Stokes and Pump pulses of 150 fs duration Fourier-limited are equally chirped to pulse durations in the 0.5 ps-2.8 ps range. In this way we reduce the spectral width of the instantaneous frequency difference to the Fourier limit of the chirped pulse duration (spectral focussing). As a proof of principle, CARS spectroscopy with high spectral resolution is demonstrated on polystyrene beads. We also show, both theoretically and experimentally, that for chirped pulse durations shorter than or comparable to the Raman coherence time, maximum CARS signal occurs for a Pump arriving after the Stokes pulse. Furthermore, we demonstrate the applicability of our CARS microscope to biological sciences by performing CARS microspectroscopy on different live cells and fixed tissue samples