On the cause of errors in reflectance vs angle of incidence measurements and the design of reflectometers to eliminate the errors.

The accuracy with which the angle of incidence phi and the reflectance R can be measured determines the accuracy with which the optical constants: n the index of refraction and k the extinction coefficient, can be determined when using the reflectance vs angle of incidence method. There are certain characteristics of reflectometers and associated equipment that contribute to the errors in measuring R and phi, for example, mechanical problems such as mirror misalignment or misalignment of the optical axes of the reflectometer and source of radiation, optical problems such as nonuniform illumination and nonuniform detector response, fluctuations in intensity of the radiation source and stray light. A discussion of these errors and ways to eliminate or alleviate them is presented, and it is shown how these correcting features can be incorporated into the design of a reflectometer.