Dehydration processing of Er3+-doped barium gallo-germanate glasses with ultra-low hydroxyl absorption for near and mid-infrared applications

In barium gallo-germanate glasses, the extrinsic absorption losses from hydroxyl (-OH) groups are mostly due to the hygroscopic nature seen in the glass, its raw precursors and from the environment during the melting process. Their vibrations (harmonic or overtone) cause detrimental absorption bands in the infrared region which limit their use as host materials for rare-earth ions emitting in the infrared. It is therefore essential to minimize the concentration of (-OH) groups in the glass. Here, we present a dehydration method to prepare barium gallo-germanate glasses at high temperature (>1500 degrees C) under a controlled atmosphere (Ar-filled, with 0.1 ppm O-2 and 0.1 ppm H2O) with ammonium bi-fluoride (NH4F-HF) as dehydrating agent to lower (-OH)-based absorption coefficient down to 0.006 cm(-1) at 3300 nm wavelength. This improvement allows a significant lengthening of the lifetimes of the electronic transition in the near infrared at 1000 nm (I-4(11/2) -> I-4(15/2)) and 1537 nm (I-4(13/2) -> I-4(15/2)) in the glasses with ultra-low hydroxyl content due to reduced (-OH) quenching. This work paves the way for developing efficient barium gallo-germanate solid-state laser components for sensing operation in the near and mid-infrared spectral range (1-5 mu m).