Novel far-infrared optically detected cyclotron resonance (FIR-ODCR) techniques are used to investigate GaAs epilayers and the results are compared with conventional cyclotron resonance performed at far-infrared frequencies and ODCR at microwave frequencies. The FIR-ODCR technique shows remarkable resolution and sensitivity and has been applied to investigations of the electronic structure of low-dimensional systems. In particular, cyclotron resonance has been optically detected in a GaAs/GaAlAs multiple quantum well (MQW) sample and compared with ODCR results performed at microwave frequency. Multi-single quantum wells (MSQW) in an MBE GaAs/GaAlAs structure with different well thicknesses have also been investigated, and by detecting cyclotron resonance via the FIR-induced changes in the luminescence of the separate wells, the power of the technique to investigate the cyclotron resonance mass versus well thickness in a single sample has been demonstrated. Finally, the experimentally determined values of effective mass for different well widths are compared with the theoretical results, showing good agreement.