Femtosecond interferometric photoacoustic spectroscopy using incoherent light

An interferometric phase-modulated femtosecond wave packet technique has been combined with photoacoustic detection to study rovibrational wave packets, using 30 ps (full-width-at-half-maximum) incoherent light pulses. The phase-modulated technique is particularly suited to be combined with photoacoustic detection, thanks to the adaptability of the modulation frequency of the light pulses to correspond to a resonance frequency of the photoacoustic cell. As an example to demonstrate the principle, the B-state of iodine has been chosen. The average 330 fs wavepacket period of the vibrational levels 12–15 and wave packet dephasing have been observed, identical to those which would be expected if transform-limited, 100 fs fwhm pulses had been used. It is shown that the combination of these detection techniques results into a very sensitive method for performing time-resolved experiments.