Fluorescence lifetime and 980nm pump energy transfer dynamics in erbium and ytterbium co-doped phosphate laser glasses

Abstract

Phosphate glasses are attractive laser oscillator/amplifier materials because unlike fluoride, silicate, and other laser glass materials it combines attractive properties such as good chemical durability, ion-exchangeability, high gain, low concentration quenching, and low upconversion losses. Phosphate glasses also exhibit very high solubility for rare earth ions. This feature permits the introduction of large concentrations of active ions into relatively small volumes resulting in smaller laser devices with high-energy storage capabilities. These high dopant concentrations also result in very rapid and efficient energy transfer between rare earth ions. This allows for the effective use of Yb³⁺ as a sensitizer for the Er³⁺ laser ion. Effective Er:Yb:Glass pumping, energy storage, and energy extraction involves the population of the ²F_5/2 level of Yb³⁺ (~2ms fluorescence lifetime) and transferring energy to the ⁴I_11/2 level of Er³⁺ (~500μsec transfer time); and a very rapid (< 1μsec) nonradiative decay of the Er³⁺ from the ⁴I_11/2 state (with an 8ms fluorescence lifetime). In this study we measured the fluorescence lifetime for the ⁴I_13/2 level of Er⁺³ on different glass samples with various concentrations of erbium. The data indicates that for doping levels up to 7% (wt.%) Er₂O₃ the lifetime remains above 7.0ms. Theoretically, this highly doped glass may produce greater than 20dB gain in 1cm path length. In additional fluorescence lifetime testing, ytterbium doped and erbium/ytterbium co-doped glasses samples were evaluated for concentration quenching and energy transfer rate as function of the Er³⁺ concentration rates. The effect on teh energy transfer efficiency and laser efficiency was analyzed.