Measurement of optical properties of materials in the vacuum ultraviolet spectral region.

Measurement of optical properties in the VUV depends on photometric data rather than a mixture of photometric and relative phase data. Generally the measurement technique is that of measuring the reflected intensity at a number of angles of incidence and fitting these data to a calculated reflectance curve. The actual measured reflectance values need not always be known but are helpful in the final analysis of the data. Other more specialized methods include a critical angle method and the determination of extinction coefficients from transmittance measurements. The accuracy of the reflectance methods depends on the optical properties of the material being measured and the angles of incidence at which reflectance measurements are made. Instrumental errors and the condition of the surface being measured can also cause appreciable errors in the results. Accurate values of the optical constants can be used to characterize the electronic structure of a material and to design special reflecting and transmitting coatings for use in EUV astronomy and laboratory applications and possibly for use with excimer lasers in the VUV.