ABSTRACT
The optical properties are among the most interesting of the physical properties of diamond. These include the widest spectral optical transmission range of all known solid materials [1] and, for a transparent material, an unusually high index of refraction. Such attributes, combined with extreme hardness, high thermal conductivity and chemical resistance, make diamond a material of obvious interest for optical applications. However, optical applications of diamond have traditionally been very limited because of the notoriously high cost of quality diamond, even for samples of modest dimensions. In spite of this, early experiments brought convincing evidence of the potential of diamond for optical uses. A case in point is the diamond window used as the optical port for an infrared radiometer experiment on the Pioneer Venus probe launched in 1978. This 18.2 mm diameter by 2.8 mm thick diamond window survived earth atmosphere on launch, the cold and vacuum of space, and the Venus atmosphere (largely carbon dioxide with various acids, including sulfuric acid, at temperatures of 800 K and pressures of 90 atm) [1]. Other important demonstrations included the use of single-crystal diamond as highpower laser windows. By virtue of low optical absorption combined with high thermal conductivity, the windows successfully passed CO2 laser beams with continuous wave (CW) power densities in excess of 1 MW/cm2 [2]. Such experiments demonstrated unique optical capabilities for diamond; remaining as a significant barrier for more widespread use was the prohibitive economic cost.
