Ultra long high resolution beam by multi-zone rotationally symmetrical complex pupil filter.

An ultra long high resolution beam with extension of depth of focus (DoF) in the axial direction as well as high resolution in the transverse direction has been demonstrated by a seven-zone rotationally symmetrical complex pupil filter imposed at the aperture of a focusing lens. Both amplitude and phase of the transmitted light are modulated in different zones. The scalar diffraction theory is used to optimize the zone parameters. Simulation results show that extended DoF of the beam is increased by 16 times while the spot size at the beam waist is reduced to 0.7 times.