Optical Properties of Diamond

The transmission spectrum of CVD diamond has been measured for the spectral range 0.2–100 μm. The transmission is >70% over the spectral range 0.2–100 μm except for a small dip around 4 μm. The refractive index n of diamond was determined by Peter using the Sellmeier equation. The value of n is ∼2.38 over the spectral range 1–100 μm. The high value of n (>2.41) of diamond in the visible region is responsible for its brilliance/luster. The change in the refractive index dn/dT of diamond at 632.8 nm with temperature has been measured for the temperature range 0–1000°C by Patterson. The value of dn/dT at 20°C is ∼1.0 × 10⁻⁵/°C. The IR absorption spectrum shows peaks at 1010, ∼1200, 1282, 1332, and 1365 cm⁻¹. The absorption peaks at 1090, ∼1200, and 1282 cm⁻¹ correspond to nitrogen. The absorption peak at 1365 cm⁻¹ is due to plate defects in the (001) plane, according to Woods et al. and Evans and Phaal.