Calcium (Ca) is an alkaline earth metal that is essential in various biological processes but also has various industrial applications. In its pure elemental form, it is a soft, silvery metal that reacts vigorously with water and oxidizes rapidly in air. While elemental calcium is not commonly used in optical applications, its compounds like calcium fluoride (CaF2) and calcium oxide (CaO) are of great interest in optics and photonics. Calcium fluoride is notable for its low refractive index variation with wavelength, making it a choice material for the production of optical components like lenses and windows, especially in the ultraviolet region. Calcium oxide, also known as lime, is used in the production of other materials like various types of glass and ceramics. The ability to dope calcium-containing materials with rare-earth or transition-metal ions makes them useful in laser applications as well. Overall, calcium and its compounds offer a range of desirable properties for optical, structural, and biological applications.