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.

Bessel terahertz imaging with enhanced contrast realized by silicon multi-phase diffractive optics.

Bessel terahertz (THz) imaging employing a pair of thin silicon multi-phase diffractive optical elements is demonstrated in continuous wave mode at 0.6 THz. A proposed Bessel zone plate (BZP) design - discrete axicon containing 4 phase quantization levels - based on high-resistivity silicon and produced by laser ablation technology allowed to extend the focal depth up to 20 mm with minimal optical losses and refuse employment of bulky parabolic mirrors in the imaging setup.