CONTROLLED MODIFICATION OF THE EXPANSION ORDER AS A TOOL IN MIE COMPUTATIONS

In the framework of Mie theory the involved electromagnetic fields are expanded in an infinite series of multipoles. In numerical computatio ns the summation has to be terminated after a finite number of terms ( the expansion order N), which unavoidably produces errors. On the othe r hand, it is known that the contributions of terms of order l with x < l < N, where x is the dimensionless size parameter, are highly local ized, i.e., these contributions appear as sharp peaks in resonance spe ctra. We show that it is possible to specify the expansion order in a controlled manner to extract certain features from Mie spectra. This c ontrolled modification of the expansion order can be used as a high-pa ss, low-pass or bandpass filter. Formulas that serve as linewidth (fre quency) and resonance-order filters are given, and their usage is demo nstrated. (C) 1998 Optical Society of America.