An algebraic method to calculate the optical constants for a weakly absorbing thin film from the spectrum of normal reflectance is described. The calculation of the refractive index of the thin film is simplified by constructing a midpoint envelope through the reflection spectrum. If a portion of the spectrum includes a region where the film is nonabsorbing, the results can be used to calculate an algebraic solution for the refractive index and the absorption coefficient of the thin film throughout the entire spectrum. The method is used to determine the constants for a coating of alumina on a glass substrate. The results are compared to the calculation from the extrema of the spectrum.
© 2007 Optical Society of America
Optics at Surfaces
Original Manuscript: November 30, 2006
Revised Manuscript: February 21, 2007
Manuscript Accepted: April 16, 2007
Published: July 6, 2007
Stephen Humphrey, "Direct calculation of the optical constants for a thin film using a midpoint envelope," Appl. Opt. 46, 4660-4666 (2007)