Modeling of a radial laminated GRIN lens: design and achievable performance of a dual-band infrared triplet with such a lens

Subject of study. This study examines the initial design of an optical system that incorporates thin homogeneous lenses, an infinitely thin model of a thick radial gradient-index lens, and a high-aperture dual-band infrared triplet developed based on this initial configuration. Aim of study. The objective of this study is to outline the computational stages involved in designing an optical system with a coaxial laminated radial gradient-index lens and to demonstrate the achievable performance of a high-aperture dual-band infrared objective composed of two homogeneous lenses and one thick radial gradient-index lens. Method. The study employs theoretical analysis, computer modeling, and optimization using Zemax optical design software. Main results. The proposed infinitely thin model of a coaxial laminated radial gradient-index lens, which maintains the same optical power and chromatic focal shift as its thick counterpart, serves as an effective starting point for optical system development. This model, combined with thin homogeneous lenses separated by air gaps, provides a strong foundation for optical system design. Given a known refractive-index distribution of the gradient-index lens, the optimal combination of optical materials for the homogeneous lenses, as well as the most effective ratio of optical powers for all system components, can be determined by solving the relevant system of equations for achromatization, apochromatization, or superachromatization. The effectiveness of the proposed approach and its ability to achieve high optical performance in a dual-band infrared triplet, consisting of two homogeneous lenses and one gradient-index lens, are demonstrated through the design of a system that incorporates a coaxially laminated radial gradient-index lens. The combination of new chalcogenide glasses was selected as the composite material for this lens to ensure the required refractive-index distribution, which was established during the design of a triplet for the medium-wavelength infrared range (3–5 µm). The layout, design parameters, and optical performance of the calculated dual-band (3.5–5 µm and 8–11.9 µm) triplet are presented. The triplet has a focal length of 40 mm, an f -number of 0.98, and a numerical aperture of 0.45 in the image space. Within an angular field of view of 19.5°, the triplet produced an image with a contrast of 0.54 at a spatial frequency of 30mm −1 , while its distortion modulus remained below 0.4%. Practical significance. The results of this study confirm the feasibility of developing simple, high-aperture dual-band infrared objectives based on coaxially laminated radial gradient-index lenses.