<title>Kinoforms with increased depth of focus</title>

Abstract

Techniques for calculation of two types of kinoform optical elements with increased causticdepth are presented: first, the elements that produce an image of the axial point as a straight line without projective transformation (axicons); second, the elements that extend caustic without changes in projecting properties of the optical system (generalized zone plates - GZP). The transmission function of kinoform axicons is determined from the second-order differential equation derived from the integral Kirchhoff-Fresnel approximation with the stationary phase technique for the given intensity distribution along the focal line. It is shown that with the given procedures one can calculate axicons that provide arbitrary desired intensity distribution along the focal line for the given amplitude distribution of the field of the illuminating lightwave. Low concentration of radiation is an important feature of axicon focusing that limits its application. Therefore, modification of lens caustic by introducing controlled aberrations is of particular interest. It is suggested to determine GZP zone topology with the tautochronizm principle and the requirement of concentration of power of the radiant energy flow from a ring zone of small width to a focal line of small length. The produced samples of kinoform axicons and GZPs have ben experimentally studied.