Multiple plane-wave scattering techniques are extended to analyze the diffraction of light by adjacent ultrasonics of frequency ratio 1:m to include the near-Raman–Nath regime. This is done first by modifying the existing theory, developed for the diffraction of light by sound at frequency Ω, to the general case of light–sound (frequency mΩ) interaction and thereafter deriving the coupled equations for the diffracted orders in each sound column. Results for some special cases are compared with previously published work.