An azimuthally polarized light source for the optical near field

In near field scanning optical microscopy (NSOM) a sharp tip with a defined aperture allows for direct scanning and subwavelength imaging of samples that otherwise cannot be excited from the far field. To control the interaction between tip and sample ideally a specifically prepared polarization state of light is desirable [1-3]. By coupling a Gaussian beam with an optimized elliptical polarization into a single mode optical fiber, which tapers down to a well-chosen μm scale diameter and undergoes a 60 degrees bend, we can reproducibly prepare an azimuthal polarization state at the tip aperture.