Amplification of a propagation invariant vector flat-top beam

Abstract

Flat-top or super-Gaussian beams have found applications in many diverse areas, particularly in laser materials processing. The creation of at-top beams requires an infinite spatial frequency spectrum and as at-top beams are not eigenmodes of the free space wave equation only approximations of at-top beams can be created. There exists a myriad of techniques to select such beams and while the majority these approaches can be efficient, these outputs are typically at a fixed plane and evolve to non-at beams beyond that plane. Methods to increase the depth of focus of at-top beams include the use of specially designed diffractive elements. These approaches hold well for larger beams, however, they are sensitive to the input beam size and the performance is drastically reduced for smaller beams. An attractive approach is the selection of propagation invariant vector at-top beams through the superposition of a Gaussian beam and a vortex beam of orthogonal polarizations. Such beams have been selected through Spatial Light Modulators (SLM) and hold a at plateau through the target plane of a convergent lens. The poor power handling capability of the SLM, however, restricts its application at higher powers. In this work we explore the amplification, through a single stage end-pumped amplifier, of vector at-top beams as selected through a Mach Zehnder interferometer. We demonstrate stable output properties and up to a 3x increased power output as compared to each beam in the corresponding superposition. This approach presents a useful advance in at-top beams for high power applications.