Pulse shaping for mode-selective ultrafast coherent Raman spectroscopy of highly scattering solids

Abstract

We report on mode-selective ultrafast coherent anti-Stokes Raman spectroscopy (CARS) of a powder of sodium dipicolinate. We produce a pair of stretched laser pulses with precisely adjusted matching chirp rates. We use the pulses for frequency-resolved excitation of coherent molecular vibrations in this highly scattering medium. The induced oscillations are probed with the third delayed ultrashort laser pulse. Since the attained spectral width of the pump-Stokes excitation band is on the order of the spacing between the Raman lines, time-resolved CARS measurements reveal single-mode as well as double-mode coherence decay dynamics, depending on the timing between the pump and Stokes pulses. For a fixed probe pulse delay, the sweeping of the arrival time for one of the preparation pulses maps out the CARS spectrum of the analyte.