Abstract

The talk deals with molecular high-resolution spectroscopy in the time domain, more specifically with quantum beat spectroscopy. This linear and essentially Doppler-free method yields a resolution power limited only by the lifetime of the excited state, which in the present case amounts to ≤ 200 kHz. A Fourier transform limited laser pulse of ~ 5ns pulse width prepares coherently excited molecular eigenstates within its time-energy uncertainty. The time evolution of this superposition state, being subject to a period phase change, is then monitored by the fluorescence decay and Fourier transformed into the frequency domain. Quantum beat spectroscopy is applied for studying the structure and dynamics of electronically excited polyatomic molecules in a supersonic jet, but is equally well applicable to the electronic ground state, if the IR-UV pump-probe technique is introduced in conjunction with the fluorescence detection, as has recently been demonstrated.

© 1994 IEEE