The Elsasser integral expression representing absorption by a periodic line pattern is evaluated analytically and compared with a numerical integration of the exact absorption expression. A series is found which represents the integral for all values of the parameters.
WALTER S. SEITZ and DEAN V. LUNDHOLM, "Elsasser Model for Band Absorption; Series Representation of a Useful Integral," J. Opt. Soc. Am. 54, 315-316 (1964)