Accurate optical modeling of VO2 thin films requires reliable knowledge of the complex dielectric function, which is known to depend sensitively on the fabrication method, substrate, and post-deposition processing. In this work, we report a phenomenological dielectric function model for ultrathin (below 50 nm thick) VO(2)films deposited by atomic layer deposition and crystallized by post-deposition annealing. Dielectric function models for both the insulating and metallic phases are provided, along with an effective medium description that enables optical modeling through the phase transition. Variable-angle spectroscopic ellipsometry measurements spanning from the ultraviolet to infrared are used to extract the complex dielectric function in both the insulating and metallic phases of VO2. The dielectric response is parameterized using Kramers-Kronig consistent oscillator models, yielding a single complex dielectric function that provides excellent agreement with all measurements across the full spectral range. The dielectric function reported here provides the input necessary for optical modeling of ultrathin atomic layer deposition-grown VO2 layers. (c) 2026 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Self‐Oscillatory behavior in soft matter/ambient interfaces is comparatively rare and less extensively characterized than in physical, astrophysical, or biological contexts. This paper reports the first experimental observation of redox‐driven self‐oscillations at the soft‐matter/ambient interface of a photochromic thiazolothiazole‐embedded polymer. The temporal characteristics of this photochromic material were investigated using spectroscopic ellipsometry. It is observed that under short‐term and sustained exposure conditions, the system exhibits autonomous, periodic optical changes. These changes are facilitated by a reversible electron transfer cycle involving the thiazolothiazole unit, a cross‐linked polymer matrix, and ambient molecular oxygen. These oscillations are confined to the oxygen‐exposed interface, indicating that molecular oxygen plays a critical role in sustaining the redox loop. Dynamic ellipsometry enables the precise characterization of these subtle changes. The presented findings reveal a previously unexplored regime of self‐sustained interfacial dynamics in photo‐responsive soft matter. Furthermore, dynamic spectroscopic ellipsometry is established as a powerful tool for probing real‐time, light‐induced oscillatory behavior. In combination with existing metamaterial designs, self‐oscillating polymer systems may provide a novel building block for dynamic metamaterials. Such dynamic metamaterials would enable a deterministic, oscillatory change in the amplitude, phase, or polarization of reflected and/or transmitted electromagnetic radiation without external stimuli.

The increasing demand for optical technologies with dynamic spectral control has driven interest in chromogenic materials, particularly for applications in tunable infrared metasurfaces. Phase-change materials such as vanadium dioxide and germanium–antimony–tellurium, for instance, have been widely used in the infrared regime. However, their reliance on thermal and electrical tuning introduces challenges such as high power consumption, limited emissivity tuning, and slow modulation speeds. Photochromic materials may offer an alternative approach to dynamic infrared metasurfaces, potentially overcoming these limitations through rapid, light-induced changes in their optical properties. This manuscript explores the potential of thiazolothiazole-embedded polymers, known for their reversible photochromic transitions and strong infrared absorption changes, for use in tunable infrared metasurfaces. The material exhibits low absorption and a strong photochromic contrast in the spectral range from 1500 cm−1 to 1700 cm−1, making it suitable for dynamic infrared light control. This manuscript reports on infrared imaging experiments demonstrating the photochromic contrast in thiazolothiazole-embedded polymer, and thereby provides compelling evidence for its potential applications in dynamic infrared metasurfaces.

In this paper, the infrared dielectric function of photochromic dipyridinium thiazolo[5,4-d]thiazole embedded in polymer is reported. Bulk thiazolo[5,4-d]thiazole-embedded polymer samples were prepared by drop casting and dehydration in room temperature. The samples were investigated using spectroscopic ellipsometry before and after irradiation with a 405 nm diode laser in the infrared spectral range from 500 cm-1 to 1800 cm-1. The model dielectric functions of the thiazolothiazole embedded polymer film for its TTz2+ (unirradiated) and TTz0 (irradiated) states are composed of a series of Lorentz oscillators in the measured spectral range. A comparison of the obtained complex dielectric functions for the TTz2+ and TTz0 states shows that the oscillators located in the spectral ranges 500 cm-1 - 700 cm-1, 1300 cm-1 - 1400 cm-1, and 1500 cm-1 - 1700 cm-1 change in both amplitude and resonant frequency upon transition between the states. Additionally, a resonance at approximately 1050 cm-1 exhibited a change in oscillator amplitude but not resonant frequency due to the photochromic transition.

This work focuses on the characterization of the complex dielectric function of a polymer material, which is UV-cured dielectric ink 1092, used in the DragonFly IV 3D inkjet printer. Infrared spectroscopic ellipsometry was performed over the spectral range of 300–4000 cm−1 at multiple angles of incidence to extract both real and imaginary components of the dielectric response. In addition, polarized transmission measurements were taken over the spectral range from 300–6000 cm−1 to aid in characterization. We report an isotropic dielectric function model that is composed of oscillators with both Gaussian and Lorentzian broadening. This model reveals strong absorption bands at 925–1500 cm−1, 1600–1775cm−1, and 2840–3000 cm−1 while otherwise appearing largely transparent. This parameterized dielectric function is critical in first-principles modeling of infrared optical components and metamaterials fabricated using this polymer.

The combination of two periodic dielectric stacks is presented as an alternative to introducing defect layers for inducing a narrow transmissive region within the reflective photonic bandgap. This method increases the overall bandgap width when compared with a single periodic stack with a defect. While the transmissive band is not as narrow as in the defect design, the transmission region does demonstrate less sensitivity to layer thickness non-uniformity. The dual-stacked photonic crystal may be more compatible with fabrication by two-photon polymerization for inducing a transmission band within the photonic bandgap.

Calibrating thermal detection systems for target recognition and accuracy can be challenging when live assets are not an option as a target. Infrared scene projection provides a cost effective and realistic alternative to assess missile capability. Infrared scene projection systems allow the generation of a thermally simulated scene for hardware-in-the-loop calibration of missile targeting. Previously, infrared scene projection technology has used resistor arrays, digital micromirror devices and laser diode arrays to name a few. Recent advancements in dynamic metamaterials provide a novel approach for the design of an infrared scene projection system. Reciprocal plasmonic metasurfaces are a metal-insulator-metal configuration of high aspect ratio dielectric pillars with sub-wavelength periodicity contained between a conductive top and bottom layer. Reciprocal plasmonic metasurfaces display an extreme sensitivity to ambient refractive index. This sensitivity in synergy with a conformal coating of a phase change material, such as vanadium dioxide, provide an excellent mechanism to implement a spatial light modulator as the scene generation component of an infrared scene projector. We report on the operating mechanism of the metasurface and characterize its sensitivity to changes in the ambient refractive index by applying a thin, conformal layer of aluminum oxide. We then expand on the experimental results by employing dielectric function data of optically characterized vanadium dioxide to inform calculations for predicting the effects of a thin conformal coating applied on the metasurface. Results indicate that pairing the sensitive metamaterial with the fast switching optical properties of vanadium dioxide provide a novel platform for infrared scene generation.

Water-soluble dipyridinium thiazolo[5,4-d]thiazole (TTz) compounds are incorporated into inexpensive poly(vinyl alcohol) (PVA)/borax films and exhibit fast (<1 s), high-contrast photochromism, photofluorochromism, and oxygen sensing. Under illumination, the films change from clear/yellow TTz(2+) to purple TTz(center dot+) and then blue TTz(0). The contrast and speed of the photochromism are dependent on the polymer matrix redox properties and the concentration of TTz(2+). The photoreduced films exhibit strong, near-infrared light (1000-1500 nm) absorbances in addition to visible color changes. Spectroscopic ellipsometry was used to establish the complex dielectric function for the TTz(2+) and TTz0 states. Incorporating non-photochromic dyes yields yellow-to-green and pink-to-purple photochromism. Additionally, when illuminated, reversible photoactuation occurs, causing mechanical contraction in the TTz-embedded films. The blue film returns to its colorless state via exposure to O-2, making the films able to sense oxygen and leak direction for smart packaging. These films show potential for use in self-tinting smart windows, eyeglasses, displays, erasable memory devices, fiber optic communication, and oxygen sensing.

As advancing technology pushes to further miniaturize systems while increasing processing power, optical structures which offer dynamic tunability are becoming ever more valuable. Diffractive gratings popularly offer high efficiencies and can be readily designed to provide polarization sensitivity, making them useful as dynamic structured optics. Recently, slanted wire gratings compatible with fabrication by two-photon polymerization were investigated for their ability to be mechanically tuned. Potential applications for this grating may be in mechanical sensing and beam splitting. In this study, we investigate an additional degree of tunability not previously considered by exploiting the polarization sensitivity as well as the mechanical. It is observed that the population of the -1(st), 0(th), and +1(st) transmitted orders are sensitive to changes between x- and y-axis polarization.

A bi-directional dual-band meta-surface antenna designed to operate at 20 GHz in the longitudinal direction and 80 GHz in the transverse direction is described and simulation results are presented.

Reciprocal plasmonic metasurfaces exhibit perfect absorption and very high sensitivity to ambient refractive index changes. Synergizing these qualities with conformal phase-change-material layers enables dynamic infrared metasurfaces with easily tunable properties as demonstrated numerically.

Finite element simulations of free-standing, bi-layer wire grid polarizers, with dimensions typical for stereo-lithography, show two orders of magnitude improvement over single-layer wire grid polarizers.

The complex dielectric function of photochromic thiazolo[5,4-d]thiazole embedded in polymer is reported in the spectral range from 0.8 to 2.5 eV. Strong absorption bands in the measured spectral range are observed depending upon its redox states.

In this study, we report on the optical properties of a photochromic thiazolo[5,4-d]thiazole-embedded in polymer in the visible and near infrared spectral range determined using spectroscopic ellipsometry. The dielectric functions for the yellow (TTz(2+)) and blue (TTz(0)) states were extracted from a numerical wavelength-by-wavelength inversion of the experimental data. The extracted dielectric functions are in good agreement with a KramersKronig consistent B-spline-based model analysis of the experimental data. The thiazolo[5,4-d]thiazole-embedded polymer exhibits several strong absorption bands from the visible to the near infrared spectral range depending upon their redox states.

The diffraction efficiency of a slanted wire diffraction grating is experimentally investigated at 0.11 THz while mechanically changing the slant angle from 25° to 45°. The diffraction efficiency is found to vary by more than 50%.

Slanted wire diffraction gratings are difficult to fabricate using conventional etching approaches, due to their off-axis symmetry. In this study, we present the first fabrication of slanted wire diffraction gratings by two-photon polymerization and verify the diffractive characteristics.

Current dual-band radars consist of 2 different radar antennas with the same back-end electronics and software. There is great interest in AFRL to develop dual-band radars by using the same antenna, operating at two different frequencies, to achieve the desired efficiency as with traditional systems but without the SWaPC constraints. This article discusses radar applications of a dual-band antenna design made possible by integrating metamaterial and metasurface design elements. The metamaterial component of the design investigates the phase change properties of $VO_{2}$ as a mechanism for switching the equivalent impedance of the proposed antenna. The meta-surface component of the design investigates the size, arrangement and structure of the antenna's unit cells that allow for both dual-band behavior and beam-steering capabilities. This article discusses the application of the proposed dual-band antenna for detection of and tracking of radar targets.

Metasurfaces, in the form of perfect reflectors, have received attention for their sensing and filtering capabilities. Plas-monic metasurfaces allow for frequency filtering by controlling the input polarization. We demonstrate a frequency filtering metasurface composed of an array of subwavelength metallic pluses fabricated using two-photon polymerization.

Recent advances in additive manufacturing have enabled the fabrication of diffractive elements with tailored mechanical properties. This enables the design and fabrication of diffractive optical elements which can be tuned by applying mechanical strain. Here diffractive transmission gratings composed of slanted wires are investigated.

In this paper, the complex dielectric function of 2,5-bis(N,N-dibutyl-4-aminophenyl) thiazolo[5,4-d]thiazole is reported. Thin films of this material were obtained by spin coating on a silicon substrate. The samples were investigated using spectroscopic ellipsometry in the spectral range from 354 nm to 1907 nm at multiple angles of incidence. The ellipsometric data were analyzed using a stratified-layer model composed of a thiazolothiazole thin film, a native SiO 2 oxide, and a Si substrate. The model dielectric function of the thiazolothiazole thin film was modeled using a series of Tauc-Lorentz and Gaussian oscillators. The best-model calculated data reproduces the experimental data very well. The bandgap of TTz is reported and found to be in good agreement with density functional theory calculations reported earlier.