The scattering of acoustic and electromagnetic waves by periodic sur-
faces plays a role in many areas of applied physics and engineering.
Opti- cal diffraction gratings date from the nineteenth century and are
still widely used by spectroscopists. More recently, diffraction
gratings have been used as coupling devices for optical waveguides.
Trains of surface waves on the oceans are natural diffraction gratings
which influence the scattering of electromagnetic waves and underwater
sound. Similarly, the surface of a crystal acts as a diffraction grating
for the scattering of atomic beams. This list of natural and artificial
diffraction gratings could easily be extended. The purpose of this
monograph is to develop from first principles a theory of the scattering
of acoustic and electromagnetic waves by periodic surfaces. In physical
terms, the scattering of both time-harmonic and transient fields is
analyzed. The corresponding mathematical model leads to the study of
boundary value problems for the Helmholtz and d'Alembert wave equations
in plane domains bounded by periodic curves. In the formal- ism adopted
here these problems are intimately related to the spectral analysis of
the Laplace operator, acting in a Hilbert space of functions defined in
the domain adjacent to the grating.