  Transient imaging or light-in-flight techniques capture the propagation of an
ultra-short pulse of light through a scene, which in effect captures the
optical impulse response of the scene. Recently, it has been shown that we can
capture transient images using commercially available Time-of-Flight (ToF)
systems such as Photonic Mixer Devices (PMD). In this paper, we propose
`spatial phase-sweep', a technique that exploits the speed of light to increase
the temporal resolution beyond the 100 picosecond limit imposed by current
electronics. Spatial phase-sweep uses a linear array of light sources with
spatial separation of about 3 mm between them, thereby resulting in a time
shift of about 10 picoseconds, which translates into 100 Gfps of transient
imaging in theory. We demonstrate a prototype and transient imaging results
using spatial phase-sweep.
