Intensity maxima position shift of spirally polarized hollow Gaussian beam with radial cosine phase modulation

Abstract

The intensity maxima position shift and the focal pattern evolution principle of spirally polarized hollow Gaussian beams (HGBs), with radial cosine phase wavefront modulation, are researched by the vector diffraction theory with Debye approximation. Significant intensity maxima position shift and focal pattern transformation of spirally polarized HGBs were found by changing the value of the spiral parameter, phase parameter or beam order. The spiral parameter contributes considerably to focal splitting, the phase parameter contributes to the intensity maxima position shift, and the beam order induces a sharper radial focal pattern. When the phase parameter equals 1, the intensity maxima position shift curves dependent on spiral parameter are initially smooth, then they begin to oscillate, and their vertical coordinates gradually increase. When the phase parameter equals 2, the intensity maxima position shift curves are initially smooth, then they begin to oscillate across the focal plane along the propagation direction with increasing amplitude. The spiral parameter, phase parameter and beam order greatly affect the intensity distribution, with the appearance of many novel focal patterns in evolution process, including intensity bowl, spheroidal shell and intensity ring. Spirally polarized HGBs with radial cosine phase modulation may be applied widely in optical manipulation, particle limitation systems, laser surface modification and laser direct writing techniques.