Formation of Bessel light beams with a subwavelength diameter of the axial maximum for diagnostics and nonlinear photolithography of semiconductor materials

Subject of study. This study investigated the schematic solutions of optical systems for forming vector Bessel light beams with a subwavelength diameter of the axial maximum. The aims of the study are to develop optical schemes for the formation of Bessel light beams with a large numerical aperture based on a combination of refractive and reflective conical optical elements and determine application methods for zero- and higher-order vector Bessel light beams to form 3D subsurface cylindrical and tubular microstructures in solids (particularly, silicon). Method. In this paper, to solve this problem, it is proposed to use schemes based on reflective conical optical elements. The first scheme is based on a combination of refractive and reflective conical elements; the second scheme is similar to the first, but to eliminate the dependence of reflection losses on polarization and also to achieve a higher value of the numerical aperture, it uses an additional optical element in the form of a truncated cone. Main results. Two types of optical schemes are proposed for forming zero- and higher-order vector beams. They are distinguished by a large numerical aperture and a high ratio of the diffraction-free region length to the main maximum diameter of the Bessel light beam. This is due to the reflective optical elements in the optical schemes. The influence of polarization of the vector Bessel light beams on the field profile is analyzed. Analytical equations are derived for the intensity radial distribution of TH- and TE-polarized vector Bessel beams (and their superpositions), which provide the subwavelength size of the axial maximum. The conditions for the formation of 3D subsurface microstructures in semiconductor plates are studied. It is shown that, by means of a nonlinear photolithography process, TE-polarized Bessel beams can form tubular structures in a semiconductor plate, whereas TH-polarized Bessel beams and TE-TH-superposition can create tubular and cylindrical microstructures. The microstructure type and its size can be controlled by varying the cone angle. Practical significance. The proposed vector Bessel light beam optical shapers are promising for applications in submicrometer optical microscopy and nonlinear photolithography in semiconductors.