Chirped pulse control methods for imaging of biological structure and dynamics

Advancements in coherent control of vibrational dynamics lie in the development of novel noninvasive imaging techniques that provide information about biological species with molecular specificity. Of particular interest is development of coherent anti-Stokes Raman scattering (CARS) spectroscopy that contains vibrational finger-prints of molecules. CARS is a nonlinear optical process utilizing ultrafast laser pulses to generate strong, molecular-specific signals. Biological imaging techniques based on CARS employ selective excitation of Raman transitions and involve ultrafast laser pulse manipulation. We show that linearly chirped femtosecond pulses may be efficiently used for vibrational mode selective excitation in stimulated Raman scattering. Chirped pulse adiabatic passage is demonstrated in two-photon Raman transitions implementing a pump and Stokes pulses having opposite linear chirps before pulse amplitude reaches maximum, and same chirps after. This approach allows one to selectively excite molecular modes in a wide range of field parameters and with high chemical sensitivity.