Femtosecond Coherent Raman Spectroscopy in Biomolecules

We present a scheme for identification of biomolecules in real time by using Coherent Anti-Stokes Raman Spectroscopy (CARS) with femtosecond pulses. The nonlinear interaction of the pulses with the molecules is calculated analytically as well as numerically and comparison is made with the experimental results. We show that the commonly used rotating wave approximation needs to be waved for our fast dephasing molecules. Propagation effects are simulated, in addition to the nonlinear interaction, and it is shown how one needs to balance the electronic resonance enhancement and the losses due to absorption, in order to maximize the signal at the output of the optically dense medium. In the transient regime, we present and analyze the generation of polarization beats. These beats are generated due to the very broad bandwidth of the femtosecond pulses, which allows for the coupling of more that one vibrational modes at a time.