An improved theoretical analysis of a far forward scattering method is presented. It is further confirmed by the authors' experiments, performed at millimeter wavelengths. Success of introducing the plasma wave damping effect into the theoretical analysis has made it possible to explain the asymmetric intensity profile observed in some far forward scattering experiments, and to establish this method as a powerful diagnostic technique for measurement of plasma waves (in particular their wavenumber and damping rate) in various plasmas.