Geometric optics for wave propagation around electron cyclotron resonances

The complications encountered in applying geometric optics to wave propagation around electron cyclotron resonances are analyzed. It is conjectured that the usual methods are applicable as long as wave absorption is weak and the wavelength is short compared to the spatial width of the resonance, although there are much more stringent constraints for being able to apply the usual expression for the wave energy density and for the group velocity being characteristic for wave energy transport. (author)