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Chromatic focal shift and resolving power of harmonic kinoform lenses in the terahertz range
G.I. Greisukh1, O.A. Zakharov1, V.L. Kashintseva2, K.A. Modestov2

1Penza State University of Architecture and Construction, Germana Titova St., 28, Penza, 440028, Russia;
2Moscow State University of Civil Engineering (National Research University), Yaroslavskoye highway, 26, Moscow, 129337, Russia

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DOI: 10.18287/COJ2032

Article ID: 2032

Language: Russian

Abstract:
This article presents formulas for calculating the optical power of a harmonic kinoform lens at an arbitrary wavelength, taking into account the dispersion of the optical material of the microstructure. These formulas are used to obtain dispersion coefficients related to various spectral ranges. It is shown that the dispersion coefficients reliably estimate chromatic focal shift only in specific spectral ranges near the wavelengths of maximum diffraction efficiency.

The spatial resolution of a harmonic kinoform lens is estimated in this article using the geometric optics approximation and taking into account that at any intermediate wavelength lying between the wavelengths of unit diffraction efficiency, the primary and secondary images formed in two adjacent diffraction orders are superimposed. The structures of images formed by a harmonic kinoform lens in polychromatic radiation with different spectra are compared, and the dependence of spatial resolution on the radiation parameters and the design parameters of the lens itself is demonstrated.

It is shown that the resolution in each spectral interval between wavelengths with unit diffraction efficiency decreases from the diffraction-limited to equal diameters of the beam patterns of the primary and secondary images of an on-axis point source. Moreover, the contrast with which point sources are resolved varies from unity to 0.2 depending on the wavelength.

These results will enable the most efficient use of harmonic lenses for focusing and collimating beams of broadband terahertz radiation.

Keywords:
harmonic kinoform lens, terahertz range, focusing properties, chromatic aberration, spatial resolution.

Acknowledgements:
The research was carried out with the financial support of the National Research Moscow State University of Civil Engineering (NRU MGSU) as part of the 2026 competition for fundamental and applied scientific research (R&D) by scientific teams of member organizations and strategic partners of the Industry Consortium "Construction and Architecture" (contract No. PGUAC/K-26 dated 05/12/2026) in order to implement the MGSU National Research University Development Program for 2025-2036 as part of the Strategic Academic Leadership Program "Priority 2030".

Citation:
Greisukh GI, Zakharov OA, Kashintseva VL, Modestov KA. Chromatic focal shift and resolving power of harmonic kinoform lenses in the terahertz range. Computer Optics 2026; 50(4): 2032. DOI: 10.18287/COJ2032.

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