  A theory has been developed to interpret time-domain Brillouin scattering
(TDBS) experiments involving coherent acoustic pulse (CAP) and light pulse
beams propagating at an angle to each other. It predicts the influence of the
directivity pattern of their acousto-optic interaction on TDBS signals when
heterodyne detection of acoustically scattered light is in backward direction
to incident light. The theory reveals the relationships between the carrier
frequency, amplitude and duration of acoustically induced "wave packets" in
light transient reflectivity signals, and factors such as CAP duration, widths
of light and sound beams, and their interaction angle. It describes the
transient dynamics of these wave packets when the light and CAP encounter
material interfaces, and the light scattering by the incident CAP transforms
into scattering by the reflected and transmitted CAPs. The theory suggests that
single-point TDBS experiments can determine not only the depth positions of
buried interfaces but also their inclinations/orientations.
