Determining the Charge of Vortex Beams by Focused Intensity After Polarization Modulation

Optical vortex beams (VB) carrying orbital angular momentum is of great importance in many fields. In this letter, combining a polarization modulation system and high NA lens, we propose a new method for detecting the topological charge (TC) value of VB. According to the focal field intensity distribution of VB after polarization modulation, we explore the correlation between the intensity and the TC of VB. The results reveal that the tightly focusing intensity represents a smallest solid spot when the TC value of VB equals the polarization azimuthal index. Based on this property, we can determine arbitrary states of VB by the focal intensity, especially in the case of higher charge.