Non-Radiative Processes In Tunable Ionic Laser Materials

Abstract

Among non-radiative processes which may be encountered in laser materials such as : self-quenching, up-conversion, excited states absorption, multiphonon non-radiative transitions, the last ones may play a particularly important role in vibronic laser materials because the tuning range is directly connected with electron-phonon coupling strength and phonon energies for vibronic radiative transitions. In this lecture we shall discuss two aspects. First we shall try to answer the question: to what extent could the large tuning range also be connected with large coupling strength and phonon energies for non radiative transitions? In such a case, one would have to trade tuning range for quantum efficiency. Which would be a limitation of a basically intrinsic nature in such laser materials. Examples taken from spectroscopic studies and lifetime measurements of Ni²+ and Co²+ doped fluorides and oxydes hosts show that effective phonon modes coupled to radiative and non-radiative transitions are different. In particular in the case of the MgF₂:Ni²+ laser, the mode mediating the tuning range appears to be at a lower energy and with a stronger coupring than the one mediating quantum efficiency trough multiphonon non-radiative decay. A second aspect that shall be discussed is the concentration enhanced electron-phonon coupling that appears to occur in such materials and which could constitute a self-quenching process of a novel type.