Fiber-format CARS spectroscopy by spectral compression of femtosecond pulses from a single laser oscillator

We demonstrate an approach to coherent anti-Stokes Raman scattering (CARS) spectroscopy/microscopy based on spectral compression of femtosecond pulses emitted by a compact Er-fiber oscillator. Spectral compression is achieved by group-velocity mismatched second-harmonic generation in periodically poled nonlinear crystals, and it allows efficient synthesis of synchronized narrow-bandwidth ( less than 10 cm(-1)) pump and Stokes pulses with the frequency difference continuously tunable up to similar to 3000 cm(-1). CARS signal enhancement by up to 3 orders of magnitude is obtained by interferometric superposition with a phase-coherent local oscillator field, also synthesized by spectral compression. (C) 2009 Optical Society of America