Optical sapphire ball lens and half ball lens are both made from Al203, it's ideal for demanding applications (such as laser systems). They have a lot of advantages: 1/ Stronger than standard optical glass,they have extreme surface hardness, high thermal conductivity, high dielectric constant and resistance to common chemical acids and alkalis. 2/ Transmits Wavelengths Ranging From UV to Mid-Infrared (0.2 - 5.5µm.) Materials characteristic Refractive index (nd) 1.768 Coefficient of dispersion (Vd) 72.2 Density (g/cm3) 3.97 TCE (μm/m) 5.3 Soften Temperature () 2000 Knoop hardness (kg/mm2) 2200 About sapphire materials for our ball lenses We only choose the best sapphire material to process the ball lens and hemispherical half ball lenses for our customers. As you know, sapphire has higher performance and higher purity near the center in the process of growing. So only the ball lens made from this part of the material has better performance.