TY - JOUR

T1 - Application of noncontact terahertz surface plasmon interferometry for determination of optical constants of thin tetraaminodiphenyl films

AU - Gerasimov, V. V.

AU - Vanda, V. S.

AU - Lemzyakov, A. G.

AU - Azarov, I. A.

AU - Nikolaev, N. A.

AU - Stepanov, V. A.

AU - Fromichev, D. V.

AU - Nikitin, A. K.

N1 - V.V. Gerasimov, V.S. Vanda, A.G. Lemzyakov, I.A. Azarov, N.A. Nikolaev, V.A. Stepanov, D.V. Fromichev, A.K. Nikitin, Application of noncontact terahertz surface plasmon interferometry for determination of optical constants of thin tetraaminodiphenyl films, Optics and Lasers in Engineering, Volume 206, 2026, 110026, ISSN 0143-8166, https://doi.org/10.1016/j.optlaseng.2026.110026. The study was supported financially by grant No. 25-22-20008 from the Russian Science Foundation and by the Government of the Novosibirsk Region (https://rscf.ru/project/25-22-20008/).

PY - 2026/11

Y1 - 2026/11

N2 - The article presents a new noncontact plasmonic refractometry method for determination of the optical constants of weakly absorbing micron-thick dielectric layers in the THz range from measured characteristics (the refractive index and propagation length) of surface plasmon polaritons (SPPs) in a sputtered gold – test dielectric layer – air structure. The method is implemented using a plasmonic Michelson interferometer and quasi-monochromatic radiation with wavelength λ = 141 μm (2.1 THz) of the Novosibirsk free-electron laser (NovoFEL). The optical constants of films under study were determined using the actual effective optical constants of the skin layer of deposited gold, which had been determined from the SPP characteristics in an experiment with a calibrated dielectric coating of zinc sulfide of micron thickness. From the measurement results, the optical constants of tetraaminodiphenyl (TADPh) films with thickness d= 1 – 4 μm, utilized in pyroelectric THz radiation detectors, were determined for the first time at this λ. It has been found that the accuracy in the determination of the film extinction coefficient increases with the excess of the SPP energy absorbed in the film over the SPP ohmic losses in the metal, as well as at low values of the film refractive index n. The minimum optical thickness of film that can be identified by this method is nd / λ ≈ 0.01, and the minimum equivalent absorption level A ≈ 0.1%, which is an order of magnitude lower than in other known methods applied in the THz range. The revealed advantages of the THz surface plasmon refractometry demonstrate a potential for scientific research and various THz photonics applications.

AB - The article presents a new noncontact plasmonic refractometry method for determination of the optical constants of weakly absorbing micron-thick dielectric layers in the THz range from measured characteristics (the refractive index and propagation length) of surface plasmon polaritons (SPPs) in a sputtered gold – test dielectric layer – air structure. The method is implemented using a plasmonic Michelson interferometer and quasi-monochromatic radiation with wavelength λ = 141 μm (2.1 THz) of the Novosibirsk free-electron laser (NovoFEL). The optical constants of films under study were determined using the actual effective optical constants of the skin layer of deposited gold, which had been determined from the SPP characteristics in an experiment with a calibrated dielectric coating of zinc sulfide of micron thickness. From the measurement results, the optical constants of tetraaminodiphenyl (TADPh) films with thickness d= 1 – 4 μm, utilized in pyroelectric THz radiation detectors, were determined for the first time at this λ. It has been found that the accuracy in the determination of the film extinction coefficient increases with the excess of the SPP energy absorbed in the film over the SPP ohmic losses in the metal, as well as at low values of the film refractive index n. The minimum optical thickness of film that can be identified by this method is nd / λ ≈ 0.01, and the minimum equivalent absorption level A ≈ 0.1%, which is an order of magnitude lower than in other known methods applied in the THz range. The revealed advantages of the THz surface plasmon refractometry demonstrate a potential for scientific research and various THz photonics applications.

KW - Терагерцовый диапазон

KW - Слабо поглощающие тонкие диэлектрические слои

KW - Оптические константы

KW - Поверхностные плазмонные поляритоны

KW - интерферометрия

KW - Пироэлектрическая пленка

KW - Terahertz range

KW - Weakly absorbing thin dielectric layers

KW - Optical constants

KW - Surface plasmon polaritons

KW - Interferometry

KW - Pyroelectric Film

UR - https://www.mendeley.com/catalogue/a7248478-4728-33ca-a761-0e2c07eefba3/

UR - https://www.scopus.com/pages/publications/105045690652

U2 - 10.1016/j.optlaseng.2026.110026

DO - 10.1016/j.optlaseng.2026.110026

M3 - Article

VL - 206

JO - Optics and Lasers in Engineering

JF - Optics and Lasers in Engineering

SN - 0143-8166

ER -