Polarization coupling of vector Bessel-Gaussian beams

We report polarization coupling of radial and azimuthal electric field components of a vector light beam as predicted by the fact that the vector Helmholtz equation is expressed as coupled differential equations in cylindrical coordinates. To clearly observe the polarization variation of a beam as it propagates, higher order transverse modes of a vector Bessel-Gaussian beam were generated by a gain distribution modulation technique, which created a narrow ring-shaped gain region in a Nd:YVO4 crystal. The polarization coupling was confirmed by the observation that the major polarization component of a vector Bessel-Gaussian beam alternates between radial and azimuthal components along with the propagation.