Sensitive femtosecond wave-packet spectrometer

We developed a highly sensitive femtosecond pump-probe spectrometer suitable for observation of ultrafast phenomena such as wave-packet dynamics and phase relaxation. Unlike the conventional pump-probe spectroscopy, our method does not require lock-in amplifiers. Selective detection of nonlinear signal is possible by combination of a rapid-scanning delay stage and multichannel DC-cut amplifiers, which is the core of our new method. Simultaneous measurement of spectra is also realized with short acquisition time less than 50 min. The detection limit is up to 1 × 10−5. This new method enables us to trace detailed dynamics of vibrational wave packet in condensed matters, and provides information of the potential energy surface and dephasing process.