Femtosecond Laser Microfabrication of Pancharatnam-Berry Phase Elements for the Formation of Optical Needles in Transparent Materials

Summary form only given. Geometrical phase (also known as Pancharatnam-Berry phase [1,2].) elements and their applications are booming nowadays: from devices like high NA metalenses to special optics like s-waveplates [3], from wavelengths in the ultraviolet to the THz diapason. The reason behind such flexibility is due to variety of different production approaches - lithography based, sculptured coatings etc. and due to the varying orientation and individual properties of sub-elements of the GPE. Such elements can act as both scalar and vectorial diffractive optical elements (or as shapers of the spatial spectra of the input beam), but usually their vectorial properties are largely ignored due to the complexity of mastering phases and amplitudes of both transverse components. Here, we propose a new polarization independent approach, which enables us to encode information into the both x and y components of the geometrical phase element. We report on our numerical study on the efficiency and feasibility of such elements. Moreover, we use a femtosecond laser based setup to inscribe nanogratings in the bulk of the glass (type 2 modification of bulk transparent material, see Ref. [3]). Formation of nanogratings with slow and fast axes aligned, respectively, parallel and perpendicular to the polarization of the incident laser pulse. By controlling the orientation and retardance of those nanogratings we effectively manufacture a GPE, where the amplitudes of the x and y components are encoded independently.