APODIZED ANNULAR-APERTURE DIFFRACTIVE AXICONS FABRICATED BY CONTINUOUS-PATH-CONTROL ELECTRON-BEAM LITHOGRAPHY

Binary diffractive axicons, designed to generate a uniform axial line focus over a specified interval, are fabricated by electron beam litho graphy. Continuous-path-control mode and dynamic beam expansion of a l ow-voltage electron beam pattern generator are employed to avoid quant ization errors in the patterning of the circular zones. Apodization by local control of diffraction efficiency is shown to be an effective m ethod to reduce axial intensity oscillations along the focal line. A n ovel split-groove apodization method is introduced to suppress second- order interference. (C) 1998 Elsevier Science B.V. All rights reserved .