Cyclotron resonance and measurements of the hole mass in La_2-xSr_xCuO₄films

Using time-domain terahertz spectroscopy in pulsed magnetic fields up to 31 T, we measure the terahertz optical conductivity over a broad doping range of cuprate La_2-xSr_xCuO₄ thin films. We observe systematic changes in the circularly polarized complex optical conductivity that are consistent with cyclotron absorption of p-type charge carriers.   We have measured the cyclotron mass and field dependent changes to the scattering rates over a broad doping.   We connect our observations to extant theory of the normal state electronic structure of these compounds.