  We present a two-color Kerr microscopy system based on two electronically
synchronized erbium-fiber laser oscillators with independently tunable emission
energies spanning most of the visible spectrum. Combining a spatial resolution
below 2 $\mu$m and sub-ps time resolution with high sensitivity and cryogenic
sample temperatures, it is ideally suited for studying spin and valley dynamics
in a wide range of two-dimensional materials. We illustrate its capabilities by
studying a monolayer of the common semiconducting transition metal disulfide
MoS$_2$.
