Numerical analysis of intensity distribution along the optical axis in non-paraxial diffractive lenses

Subject of study. This study investigates the longitudinal and transverse intensity distributions of laser beams diffracted by parabolic and spherical diffractive lenses and axicons. Aim of study. The aim of this study is to clarify the influence of the input parameters of lenses operating in the non-paraxial regime on the resulting intensity distribution when generating a beam with specified properties for different types of polarization. Method. A numerical analysis of the Fresnel and first-kind Rayleigh–Sommerfeld diffraction integrals is performed using quadrature formulas and parallel computing on a graphics processing unit. Main results. Depending on the numerical aperture, the profile of a diffractive non-paraxial lens may approximate that of an axicon or parabolic lens with the corresponding focal length, thereby ensuring the formation of an intensity peak. Homogeneous polarization states enable the formation of an on-axis intensity maximum through the x - and y -components of the electric field, whereas radial polarization produces an on-axis maximum through the dominant contribution of the longitudinal component. For azimuthal polarization, an axial focus can be formed by transverse components when a vortex phase is introduced into the input field. Practical significance. The results obtained in this study can be used for designing optical elements that provide controlled variations in the polarization and phase characteristics of the electromagnetic field. This expands the means of influencing laser radiation–matter interaction and improves the control of laser processing and material structuring.