Arnold Sommerfeld's Mathematische Theorie der Diffraction marks a
milestone in optical theory, full of insights that are still relevant
today. In a stunning tour de force, Sommerfeld derives the first
mathematically rigorous solution of an optical diffraction problem.
Indeed, his diffraction analysis is a surprisingly rich and complex mix
of pure and applied mathematics, and his often-cited diffraction
solution is presented only as an application of a much more general set
of mathematical results. The body of Sommerfeld's work is devoted to the
systematic development of a method for deriving solutions of the wave
equation on Riemann surfaces, a fascinating but perhaps underappreciated
topic in mathematical physics.