PRODUCTION AND USES OF DIFFRACTIONLESS BEAMS

It is proposed to obtain intense optical fields, whose form shows little change in size over long paths, through the use of either conical lenses or spherical lenses showing spherical aberration together with a single projecting lens. The conical lens is shown to produce fields whose transverse structure is given by a zero-order Bessel function J0, while the spherical aberrating lens produces (real or virtual) J0-like transverse structures, provided that the central portion of the aberrating lens is occluded. In all cases projection gives a J0 real-image optical structure. Intensity, size of the transverse structure, and range considerations are developed, and some aspects of optimization are discussed. A negative aberrating lens gives a long range of nearly constant size in the image field, and a universal expression is presented to describe the image size as a function of image distance for this case. Projection with an aberrating projection lens is shown to improve the constancy of the final J0 pattern size dramatically. Typical photographic results are included for beams generated by using a low-power He-Ne laser. Brief considerations of practical uses of diffractionless beams are presented.