High Repetition Rate Femtosecond Lightsource for CARS Microscopy

The use of femtosecond pulsed excitation in microscopy permits the application of nonlinear optical techniques to microscopic studies of biological samples. Among the these techniques, the method of coherent anti-Stokes Raman scattering (CARS) is particularly promising for biological imaging since it allows spectrally selective probing for specific biochemical species without the need for extrinsic markers. In order to perform spectrally resolved CARS microscopy, a multicolour tunable coherent lightsource is required. Due to the nonlinear nature of the signal generating process, the signal yield would benefit from high peak powers whereas at the sample a low dose (low average power) is wanted. Furthermore, high repetition rates would significantly enhance the image acquisition times. We have constructed a high repetition rate femtosecond multicolour lightsource based on a cavity-dumped visible optical parametric oscillator. The OPO is pumped by the second harmonic (400 nm) of a mode-locked femtosecond Ti:sapphire laser