Coherent Optical Spectroscopy of Molecules Undergoing Resonance Scattering and Radiationless Transitions: The Right-Angle Photon Echo

Abstract

Before lasers were brought to the laboratories of chemists and physicists, molecular relaxations were identified using broad band chaotic light excitation. Knowledge of the radiative decay from the photon counting rate and the quantum yield gives information about one of the most fundamental processes in chemical dynamics; radiationless transitions. From the last two decades much is known about these processes, which simply result in a change of molecular electronic state without absorption or emission of photons. and encompass a wide class of phenomena such as autoionization in atoms, predissociation, molecular electronic relaxation and energy transport in condensed media. What is not known, at least experimentally, can be outlined with the following questions: (1)Do radiationless transitions depend on the nature of the exciting photon field? (2)What is the exact nature of the state we excite? (3)What is the influence of the ensemble optical coherence on the evolution of nonradiative processes? (4)Is there a threshold for an "ergodic" behavior in large molecules?

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