Germanate glass for laser applications in ∼ 2.1 μm spectral region: A review

The growing landscape of laser applications in ∼ 2 μm spectral region leads to the development of novel transparent media that provide low attenuation solutions for high power laser applications. This includes investigating glassy media such as heavy metal oxides (e.g. tellurite and germanate), fluoride and chalcogenides as an alternative to the most efficient and widely utilized silica glass. This review article discusses the potential of a heavy metal oxide lead-germanate glass (GeO(2)-PbO-Ga(2)O(3)–Na(2)O) for ∼ 2.1 μm laser applications, with a focus on our contribution to the field. Firstly, a comparative study of commercially available silicates and fluorides with germanate glass is presented to reveal germanate to be a favorable material for 2.1 μm laser applications. Secondly, as our contribution to the field, we present the development of the first ∼ 2.1 μm small cavity single frequency laser action in a Ho(3+) doped GPGN glass that verifies its capability for ∼ 2 μm laser applications and beyond.