Nonradiative surface plasmons may be excited in a metal-coated diffraction grating by either $p$- or $s$-polarized photons if the ruling is oriented neither perpendicular nor parallel to the plane of photon incidence. Phase correlation between these surface plasmons in a 520-line/mm Ag-coated diffraction grating was observed by measuring absorption of elliptically polarized 633-nm photons at the plasmon resonance angle. The absorption measurements were made by using a photoacoustic technique. The experimental results were analyzed by a first-order perturbation theory of photoabsorption in a rough surface. This allowed us to determine the phase difference between surface plasmons excited by $p$- and $s$-polarized photons.

• Received 10 June 1983

DOI:https://doi.org/10.1103/PhysRevB.28.4211