Laser picosecond acoustics in double-layer transparent films

By the optical pump-and-probe technique, picosecond acoustic pulses are excited and detected in thin transparent double-layer films of silica and silicon nitride upon opaque chromium substrates. By taking both acoustic and optical multiple reflections into account, one can successfully model the main features of the reflectance variation. The film thicknesses, sound velocities, and photoelastic constants are derived by use of known values of the refractive indices.