Position-dependent amplitude of electromagnetically generated ultrasound in metals

An electromagnetic wave incident on a metal surface generates an acoustical wave in the metal. The amplitude of this acoustical wave is calculated as a function of depth. The theory includes the effects of a surface force, which could arise from diffuse scattering of electrons at the boundary, as well as bulk forces, i.e., the electric, collision-drag, and Bragg-reflection forces. It is shown that the amplitude at the surface differs from that of the propagating wave in the bulk. However, in the presence of a large static magnetic field applied normal to the surface, the two amplitudes approach equality. The inclusion of a surface force arising from diffuse reflection is shown to cause a qualitative modification in the behavior of the generated amplitude as a function of magnetic field.