Selective excitation of femtosecond coherent anti-Stokes Raman scattering in the mixture by phase-modulated pump and probe pulses

In this paper, we present a feasible method to realize and improve the selective excitation of femtosecond coherent anti-Stokes Raman scattering (CARS) in a mixture. We theoretically show that, by shaping both the pump and probe pulses with the π phase step, the CARS signal from one quantum system can be enhanced and simultaneously that from the other quantum system is effectively suppressed. Comparing with only shaping the probe pulse [D. Oron, N. Dudovich, D. Yelin, and Y. Silberberg, Phys. Rev. Lett., 88, 063004 (2002)], the selectivity of femtosecond CARS by shaping both pump and probe pulses can be greatly improved. Finally, we experimentally compare two shaping schemes by investigating the selective excitation of the femtosecond CARS in the mixture of dibromomethane (CH₂ Br₂) and chloroform (CHCl ₃) .