Time-resolved Microwave Double Resonance in Four Level Systems: H2CO

Experiments have been performed using time-resolved spectroscopy techniques in a four-level double resonance scheme. The time-resolved variations of radiation probing the populations of a K-type doublet of H CO have been studied as pump radiation suddenly switched on and off induces population changes between levels of another K-doublet. Non-exponential behavior with characteristic times longer than the relaxation time associated with pressure broadening has been exhibited. A theoretical treatment of this effect, using a generalized density matrix equation, is proposed. It gives reasonable agreement with the observed time dependences.