  Magnetooptical measurements of several quasi-two-dimensional (q2D) organic
conductors, which have simple Fermi surface structure, have been performed by
using a cavity perturbation technique. Despite of the simple Fermi surface
structure, magnetooptical resonance results show a dramatic difference for each
sample. Cyclotron resonances (CR) were observed for q-(BEDT-TTF)2I3 and
(BEDT-TTF)3Br(pBIB), while periodic orbit resonances (POR) were observed for
(BEDT-TTF)2Br(DIA) and (BEDT-TTF)3Cl(DFBIB). The selection of the resonance
seems to correspond with the skin depth for each sample. The effective mass of
POR seems to have a mass enhancement due to the many-body effect, while
effective mass of CR is independent of the strength of the electron-electron
interaction. The scattering time deduced from each resonance's linewidth will
be also presented.
