Strong reducing of the laser focal volume

Abstract

Many applications of lasers seek nowadays for focal spots whose corresponding volume is getting smaller and smaller in order to ensure high spatial resolution. This problem, studied by many research groups around the world, is the core of this research work which deals with controlling the focal volume of a focused laser beam. Indeed, our objective is to develop a new method based on spatial treatment of laser beams, allowing to solve, in an original and efficient manner, two fundamental issues that have not been treated satisfactorily yet, i.e. : (i) The generation of a special laser beam, which has the ability to produce a focal volume smaller than the one resulting from a more common Gaussian beam, when focused by an ordinary lens. The expected reduction factor of the focal volume is in the order of several hundreds, when the existing methods do not exceed few tenths. (ii) The decoupling between transversal and longitudinal resolutions within the focal volume, contrary to Gaussian beams whose depth of field is proportional to the square of its beam-waist radius. The method that it is developed is based on two steps: First, the laser is forced to oscillate on a high-order but single transversal mode <i>TEMp0</i>, which is secondly spatially beam-shaped thanks a proper Diffractive Optical Element (DOE) that allocates the super-resolution feature².