  Imaging with ultrashort exposure times is generally achieved with a
crossed-beam geometry. In the usual arrangement, an off-axis gating pulse
induces birefringence in a medium exhibiting a strong Kerr response (commonly
carbon disulfide) which is followed by a polarizer aligned to fully attenuate
the on-axis imaging beam. By properly timing the gate pulse, imaging light
experiences a polarization change allowing time-dependent transmission through
the polarizer to form an ultrashort image. The crossed-beam system is effective
in generating short gate times, however, signal transmission through the system
is complicated by the crossing angle of the gate and imaging beams. This work
presents a robust ultrafast time-gated imaging scheme based on a combination of
type-I frequency doubling and a collinear optical arrangement in carbon
disulfide. We discuss spatial effects arising from crossed-beam Kerr gating,
and examine the imaging spatial resolution and transmission timing affected by
collinear activation of the Kerr medium, which eliminates crossing angle
spatial effects and produces gate times on the order of 1 ps. In addition, the
collinear, two-color system is applied to image structure in an optical fiber
and a gasoline fuel spray, in order to demonstrate image formation utilizing
ballistic or refracted light, selected on the basis of its transmission time.
