  We describe a two-color pump-probe scanning magneto-optical Kerr effect
(MOKE) microscope which we have developed to investigate electron spin
phenomena in semiconductors at cryogenic temperatures with picosecond time and
micrometer spatial resolution. The key innovation of our microscope is the
usage of an ultrafast `white light' supercontinuum fiber-laser source which
provides access to the whole visible and near-infrared spectral range. Our Kerr
microscope allows for the independent selection of the excitation and detection
energy while avoiding the necessity to synchronize the pulse trains of two
separate picosecond laser systems. The ability to independently tune the pump
and probe wavelength enables the investigation of the influence of excitation
energy on the optically induced electron spin dynamics in semiconductors. We
demonstrate picosecond real-space imaging of the diffusive expansion of
optically excited electron spin packets in a (110) GaAs quantum well sample to
illustrate the capabilities of the instrument.
