Heterodyne measurement of vibrational wave packets of diatomic molecules

method is presented for reconstructing the quantum state of vibrational wave packets in diatomic molecules by a heterodyne experiment. After the preparation of a wave packet, a femtosecond laser pulse interferes with the induced polarization and the resulting signal is frequency filtered and measured by a photodetector. The conditions are analyzed under which the resulting time- and frequency-resolved photocurrent contains the information needed to recover the quantum state of the prepared wave packet. It is shown that the vibrational wave function in the excited electronic state can be measured directly without the need of involved numerical reconstruction. Simulations of the proposed experiment are performed for sodium dimers. [S1050-2947(99)05510-9].