Measurement of optical constants of CVD-diamond for short-wavelength far-infrared region

We are developing a diagnostic system using short-wavelength far-infrared lasers (40-70 /spl mu/m in wavelength) for high density and large volume plasmas. In the wavelength region, a CVD-diamond is the excellent materials for optical windows of the laser and the plasma vessel and beam splitters of a multi-channel interferometer. Using our FIR laser system, the optical constants (refractive index n, absorption coefficient /spl alpha/ and transmissivity T) of the diamond etalon have been measured precisely for 47-, 57- and 71-/spl mu/m in wavelength. The result for 57.1511 /spl mu/m light is n=2.383(0)/spl plusmn/0.001, /spl alpha/=0.32/spl plusmn/0.02 cm/sup -1/ and T=96/spl plusmn/1% (at 1.023 mm in thickness).