Spectral hole-burning of Nd³⁺-doped heavy metal fluoride glasses

The first observation is reported of persistent spectral hole-burning in fluoride glasses. Measurements were made on the 4I 9 2 → 4F 3 2 transition of Nd3+_ in ZBLAN and BIGaZYT glasses, with neodymium concentrations from 0.05 to 2 wt%. The spectral holes were observed either in absorption, or in fluorescence excitation with detection at 1.05 μm. The holes were typically a few percent in depth and their amplitude decayed non-exponentially, reaching 50% in 1 h. At 1.4 K, the holes in both fluoride glasses had a width of 150 MHz, measured in a regime where the width was independent of burning power and fluence. This broadening is much larger than observed in crystalline systems and is ascribed to dephasing by thermally activated tunneling systems. The temperature dependence of the holewidth was almost linear from 1.4 to 8 K, and differs from that reported recently in a neodymium-doped silica fiber. © 1993.