Longitudinally polarized subwavelength beam generated by focusing radially modulated Bessel-Gaussian beam

Abstract

Longitudinally polarized subwavelength beams have found many applications such as particle acceleration, single molecule dipole detection, second harmonic generation imaging, longitudinally polarization confocal microscopy. We present a radially modulated Bessel-Gaussian beam model which produces longitudinally polarized beams with high purity after being focused by high numerical aperture objective. Based on the vector diffraction theory, the electric field intensity distribution, magnetic field intensity distribution and energy flux density near the focal plane are numerically simulated. The result shows that the full-width at half-maximum is as small as 0.4λ. The method does not require a physical annulus or annular phase filter and it features high energy efficiency, high resolution, thus improving application performances.