  We report a study of magneto-optical properties in the mid-infrared region of
a series of La$_{2-x}$Sr$_x$CuO$_4$ samples with hole doping level ranging from
severely underdoped ($x=0.03$)to optimally doped ($x=0.15$). The Faraday
rotation and circular dichroism are measured in a magnetic field of 8 Tesla and
in a temperature range between 30K and 300K. The doping and temperature
dependence of infrared Hall angle is found to be understood within a simple
Drude model. A significant increase of Hall frequency is observed when the hole
doping level is reduced from optimal doping, which is compared with models of
the pseudogap.
