In this paper, the anomalous diffraction approximation method is improved for
calculating the extinction efficiency of non-spherical particles. Through
this step, the range of the refractive index of particles can be enlarged,
and the improved anomalous diffraction approximation method can be applied
easily to the calculation of extinction efficiency for the most kinds of
non-spherical particles. Meanwhile, an optimal wavelength selection algorithm
is proposed for the inversion of non-spherical particle size distribution in
the dependent mode. Through the improved anomalous diffraction approximation
method, the computation time is substantially reduced compared with the
rigorous methods, and a more accurate inversion result of particle size
distribution is obtained using the optimal wavelength selection method.