Erasable holographic gratings in Eudoped glasses

Abstract

Four-wave mixing techniques were used to establish and probe refractive-index gratings in Eu3+- doped silicate and phosphate glasses. When the Eu3+ ions are resonantly excited in one of the higher excited states, superimposed transient and permanent gratings are formed. The former are characteristic of population gratings of excited Eu3+ ions while the latter are attributed to local modifications of the glass hosts. The permanent gratings remain stable for days at room temperature. They can be erased optically by a single laser beam in resonance with a transition to one of the higher excited states of Eu3+. They also can be erased thermally by increasing the temperature to ~350 K. The time dependences of the grating buildup, decay, and erasure were measured as a function of temperature, laser power, and write beam crossing angle for each sample. The results are used to suggest a model for the permanent refractive-index change based on configuration changes in the host due to the generation of local vibrational modes by radiationless relaxation of the Eu3+ions.