Forming light beams and patterns with zero intensity central points

Abstract

In order to produce a beam with a zero intensity axial ray or to produce a beam that when focused will produce an image of a doughnut shaped pattern with a zero intensity central point, a beam with a uniform or Gaussian profile is directed to a plurality of transparent plates, arranged in pairs on opposite sides of the beam axis, such that for at least one pair, the plates have a composition and thickness different from each other, and chosen so that the transmitted light has a has a phase difference of half a wavelength for at least three different wavelengths. An additional plate with a center on the perpendicular of the line connecting the first two plates has a composition and thickness such that the light transmitted through that additional plate has a phase difference of a quarter wavelength with respect to the light transmitted through one of the plates of said first pair of plates, at at least one wavelength.

1 . In an imaging device comprising a laser producing a beam with an axis, optical apparatus for transforming the profile of said beam into a transformed profile having an area of low intensity surrounded by areas of higher Intensity and a method of projecting that transformed profile onto a specimen to be imaged, a method for improving the imaging comprising the steps:
 over a first portion of said laser beam, external from the axis of said beam, translating said first portion away from said axis, in a direction generally away from said axis towards said first portion, to form a first translated beam portion;   over at least a second portion of said laser beam translating said second portion away from said axis, in a direction generally away from said axis towards said second portion to form a second translated beam portion; and   directing said first translated beam portion and said second translated beam portion towards said optical apparatus for transforming the profile of said beam.