Excited State Absorption (ESA)
Rare earth ions can absorb additional pump or signal photons when it is already in an excited state, taking it to higher excited states from which it must relax, usually via non-radiactive decay, to the metastable state. This process does not contribute to gain, so is undesirable for efficient output.
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Related Terms: Absorption, Erbium Doped Fiber (EDF), Erbium, Excited State, Excited State Absorption (ESA), Multi-Photon and Multi-Phonon Interactions, Ytterbium