Vibrational dynamics probed by femtosecond pathlength-modulation spectroscopy

Summary form only given. Femtosecond pump-probe spectroscopy is the most popular method for real-time observation of molecular vibrations. Using this technique, however, it is very difficult to delineate various contributions to the measured signal, as they can form a coherent or incoherent superposition. Consequently, it is virtually impossible to discriminate among different classes of nonlinear phenomena of molecular vibration, for example, such as Raman echo, and beats at overtone frequencies. In this contribution, we show that the use of the pathlength-modulation technique offers a substantial improvement of the regular pump-probe spectroscopy, whereas the implementation of a double-pump measurement allows us to distinguish between coherent and incoherent types of signals.