Intrinsic and extrinsic absorption of chemical vapor deposition single-crystal diamond from the middle ultraviolet to the far infrared

Optical absorption is reported in high-quality single-crystal Type IIa diamonds grown by microwave-assisted chemical vapor deposition. Laser calorimetry and spectrophotometry were used at wavelengths from the ultraviolet to the infrared. There is minimal evidence of extrinsic absorption on or near the short wavelength side of the middle-ultraviolet (MUV) region (200-300 nm) or in the infrared absorption bands. At the long wavelength side of the MUV and extending into the visible, extrinsic absorption dominates, which is related to the amount of nitrogen and nitrogen-related lattice defects in diamond. In the samples studied nitrogen concentrations were between 10 and 40 ppb. At 10.6 mu m, the measured absorption coefficient of a representative sample is comparable with, or less than, those of the highest quality samples previously reported. Evidence is presented showing that our measurements serve as upper bounds on the absorption coefficients and call into question previous calorimetric reports of intrinsic absorption in the visible, near infrared, and at 10.6 mu m.