Removing the evanescent waves from the finite series expression of the beam shape coefficients of the Gaussian beam: a study on the remodeling effects

Abstract

This paper presents a reformulation of the finite series expressions for the beam shape coefficients (BSCs) of the Gaussian beam, distinctly separating the contributions from propagating and evanescent waves, these evanescent waves being associated with a blowing-up of the BSCs. By removing the contribution from evanescent waves, the blowing-up phenomenon is therefore eliminated. Additionally, the study investigates the beam remodeling effects of the finite series method. Unexpected far-field divergence along beam propagation and near-field oscillation structures are observed in numerical results. The analysis leads to a prediction that the finite series method inherently introduces a weak counter-propagating field component, which may account for the observed anomalies. These findings provide crucial insights for refining BSC-based beam remodeling and minimizing unphysical artifacts in practical applications.