AN ABERRATION-FREE IMAGING TECHNIQUE BASED ON FOCAL DEPTH EXTENSION

An imaging technique based on focal depth extension in active dynamic hollow cone illumination is proposed and discussed with respect to the influence of the system wave aberration. This imaging method uses a f igure (numerical) 8 shaped narrow band-pass (for non-linear image redu ction), sign correction (for amplitude/phase image selection) and medi an frequency range enhancement filter in the two-dimensional Fourier s pace. A simple analysis for the influence of the aberration shows that the present imaging technique is free from all primary aberrations ex cept for astigmatism. In addition, the effect of higher order axially symmetric wave aberrations can be corrected by the use of the aberrati on map obtained from the diffractogram of the finally reconstructed im age.