A one‐dimensional theory of the generation of ultrasonic waves by photoacoustic absorption in a composite structure is described. The model consists of a backing material, an absorbing bulk or surface film, and a sample. Variations of ultrasonic amplitude and intensity with structure dimensions, optical absorption coefficient, frequency, and material parameters are discussed and compared with reported experimental data. It was found that the important material group—for both backing and film or sample—is α(D)1/2, where α is effectively a thermal‐expansion coefficient and D is the thermal diffusivity. The relevance of the parameters in the heated volume to imaging is discussed.