title: Effect of aberrations and apodization on the performance of coherent optical systems. 3: The near field.
abstract: The effects of Gaussian apodization on the near field of a coherent optical system having -0.8 waves of third-order spherical aberration were examined. The study concentrated on the areas near the focus in the Fresnel region of an f/12 system. Computer predictions were made for four cases: unapodized-unaberrated, apodized-unaberrated, unapodized-aberrated, and apodized-aberrated. Predictions were made for cross-sectional planes perpendicular to the optical axis using Fourier techniques. Meridional plane predictions were produced using a numerical integration method for evaluating the Kirchhoff integral. Additionally, experimental data were taken to compare with the predictions. It is shown that the experimental data match the computer predictions and that apodization is an effective method for controlling the near-field ringing due to aperture effects and spherical aberrations. Additionally, fine structure corresponding to Young's double slit interference is observed in the unapodized cases.
authors.forename: D B
authors.initials: DB
authors.lastname: Allred
authors.forename: J P
authors.initials: JP
authors.lastname: Mills