Generation of an optical needle beam with a laser inscribed Pancharatnam-Berry phase element under imperfect conditions

Beams exhibiting long focal lines and small focal spot sizes are desired in a variety of applications and are called optical needles, with Bessel beams being a common example. Conical prisms are regularly used to generate Bessel beams, however, this method is usually plagued by an appearance of on-axis oscillations. In this work, we consider an optical element based on the space-domain Pancharatnam-Berry phase (PBP) to generate a high-power optical needle with a smooth and constant on-axis intensity profile. The phase in PBP elements is not introduced through optical path differences but results from the geometric phase that accompanies space-variant polarization manipulation. Our implementation is based on a type 2 modification of bulk transparent glass material, resulting in the formation of nanogratings with slow axes aligned perpendicular to the grating corrugation. We investigate both numerically and experimentally the stability of an optical needle generation under imperfect conditions. Influences of misalignments in the optical schema are investigated numerically and experimentally. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Automated summary

In this study, an optical element based on the space-domain Pancharatnam-Berry phase is proposed to generate a high-power optical needle with a smooth and constant on-axis intensity profile. The implementation involves modifying bulk transparent glass material to form nanogratings, ensuring stability even under imperfect conditions. Numerical and experimental investigations are conducted to analyze the effects of misalignments in the optical schema on the generation of the optical needle.