A simple method to measure the lifetime of excited levels of rare earth ions: Application to erbium ions in fluorophosphate glasses

A resonant technique, based on the sinusoidal modulation of the pump beam intensity, is demonstrated in the case of the precise measurement of the lifetime of the ⁴I_13/2 level of erbium ions in fluorophosphate hosts. This intensity modulation is obtained via a rotation of the polarization of the pump beam. The large signal-to-noise ratio enables the use of low pump power and apparent lifetime shortenings due to ion-ion energy transfer processes and to amplification of spontaneous emission are circumvented. A parallel with decay times deduced from usual fluorescence decay measurements is performed. Extension of the method to the spectroscopy of other rare-earth ions is discussed.