Fused Silica is formed by chemical combination of silicon and oxygen. Fused Silica is perfect optical material due to its good UV and IR transmission, low coefficient of thermal expansion. It has high stability and resistance to thermal shock over large temperature excursions, wide temperature operating range and high laser damage threshold.
The Positive Meniscus
Lenses are a convex-concave lens, but it is thicker at the center than
at the edges. They are felt polished and are used universally in the
ophthalmic industry where convention dictates that lens power be
specified in Diopters.
The Negative Meniscus Lenses are a convex-concave lens, but it is
thinner at the center than at the edges. Otherwise description is
similar to Plano Concave lenses.