IR-to-visible up-conversion mechanisms in Pr 3+-doped ZBLAN fluoride glasses and fibers

Abstract

The infrared-to visible up-conversion in Pr 3+-doped ZBLAN fluoride glasses has been investigated for different activator concentrations and for different type-materials, either bulk or fiber. Single beam experiments using continuous wave (CW) laser excitation and pulsed laser excitation allow to point out different up-conversion mechanisms, namely excited state absorption (ESA) and energy transfer up-conversion (ETU). The 2.8th power dependence of the blue fluorescence from the 3P 0 state under CW resonant pumping of the 1G 4 state indicates a dominant three-photon mechanism involving the 1D 2 state. Pulsed laser excitation shows that an ETU process is occurring. When the excitation wavelength is resonant with an ESA transition from the 1G 4 state, a two-photon process is pointed out. Concerning the red fluorescence issued from 1D 2 state, under CW excitation of the 1G 4 state, it is attributed to an ETU process which is greatly enhanced by ESA of the 1.3 μm signal, in the amplification regime in fibers. The influence of the Stark splitting and subsequent transition probabilities on the optical spectra is discussed, enlightening a behavior particular to Pr 3+ ion as compared to other rare earth ions.