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Phosphate glasses can dissolve high concentrations of rare earths and have excellent spectroscopic properties making
them useful solid-state laser materials. Solid-state lasers doped with different rare-earth ions find applications in a wide range of LIDAR (Light Detection and Ranging) and sensing applications; phosphate glasses are useful host materials for many applications in the visible and near-infrared spectral regions. For example, trivalent erbium (Er3+) doped phosphate glasses operate at the eye-safe wavelength of 1.54 μm and are used for range finding and sensing applications. Tm3+ doped solid-state lasers operating at ~ 2 μm can be used for wind-shear and turbulence monitoring. Similarly, Nd-doped metaphosphate glasses are the preferred gain medium for high-peak-power lasers used for fusion energy research because they can store optical energy at greater densities than other glass-types and can be fabricated in large sizes with high rare-earth ion concentration. This paper discusses issues affecting glass quality, with particular focus on defect formation, especially crystallisation. Avoiding crystallisation during processing is essential to form high quality laser cavities. The work presented explores some of the factors controlling these defects including contamination during melting. The crystallisation behaviour of the glass was investigated for several different phosphate glass compositions and different melting conditions, including melting duration, temperature and crucible material.
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