  Epsilon-near-zero (ENZ) materials have shown strong refractive nonlinearities
that can be fast in an absolute sense. While continuing to advance fundamental
science, such as time varying interactions, the community is still searching
for an application that can effectively make use of the strong index modulation
offered. Here we combine the effect of strong space-time index modulation in
ENZ materials with the beam deflection technique to introduce a new approach to
optical pulse characterization that we term a space-time knife edge. We show
that in this approach, we are able to extract temporal and spatial information
of a Gaussian beam with only two time resolved measurements. The approach
achieves this without phase-matching requirements (<1 micron thick film) and
can achieve a high signal to noise ratio by combining the system with lock-in
detection, facilitating the measurement of weak refractive index changes
(delta_n ~ 10^-5) for low intensity beams. Thus, the space-time knife edge can
offer a new avenue for ultrafast light measurement and demonstrates a use cases
of ENZ materials. In support of this, we outline temporal dynamics for
refractive index changes in non-colinear experiments opening avenues for better
theoretical understanding of both the spatial and temporal dynamics of emerging
ENZ films.
