  We present here the design of a sensitive Compact Faraday-modulator (CFM)
based optical magnetometer for imaging the distribution of weak local magnetic
fields inside hysteretic magnetic materials. The system developed has a root
mean square (rms) noise level of 50 mG.Hz-1/2 at a full frame rate of 1 frame
per second with each frame being of size 512 x 512 pixels. By measuring the
local magnetic field distribution in different superconducting samples we show
that our magnetometer provides an order of magnitude improvement in the signal
to noise (S/N) ratio at low fields as compared to ordinary magneto-optical
imaging technique. Moreover, it provides the required sensitivity for imaging
the weak magnetization response near a superconducting transition where a
number of other imaging techniques are practically unviable. An advantage of
our CFM design is that it can be scaled in size to fit into situations with
tight space constraints.
