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  1. Diffractive optics are structured optical surfaces that manipulate light based on the principles of interference and diffraction. By carefully designing the diffractive optical elements, the amplitude, phase, direction, and polarization of the transmitted and reflected light can be controlled. It is well-known that the propagation of light through diffractive optics is sensitive to changes in their structural parameters. In this study, a numerical analysis is conducted to evaluate the capabilities of slanted-wire diffraction gratings to function opto-mechanically in the infrared spectral range. The slanted wire array is designed such that it is compatible with fabrication by two-photon polymerization, a direct laser-writing approach. The modeled optical and mechanical capabilities of the diffraction grating are presented. The numerical results demonstrate a high sensitivity of the diffracted light to changes in the slant angle of the wires. The compressive force by which desired slant angles may be achieved as a function of the number of wires in the grating is investigated. The ability to fabricate the presented design using two-photon polymerization is supported by the development of a prototype. The results of this study suggest that slanted-wire gratings fabricated using two-photon polymerization may be effective in applications such as tunable beam splitting and micro-mechanical sensing. 
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    Free, publicly-accessible full text available July 1, 2024
  2. One-dimensional photonic crystals have been used in sensing applications for decades, due to their ability to induce highly reflective photonic bandgaps. In this study, one-dimensional photonic crystals with alternating low- and high-density layers were fabricated from a single photosensitive polymer (IP-Dip) by two-photon polymerization. The photonic crystals were modified to include a central defect layer with different elastic properties compared to the surrounding layers, for the first time. It was observed that the defect mode resonance can be controlled by compressive force. Very good agreement was found between the experimentally measured spectra and the model data. The mechanical properties of the flexure design used in the defect layer were calculated. The calculated spring constant is of similar magnitude to those reported for microsprings fabricated on this scale using two-photon polymerization. The results of this study demonstrate the successful control of a defect resonance in one-dimensional photonic crystals fabricated by two-photon polymerization by mechanical stimuli, for the first time. Such a structure could have applications in fields, such as micro-robotics, and in micro-opto–electro–mechanical systems (MOEMSs), where optical sensing of mechanical fluctuations is desired. 
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    Free, publicly-accessible full text available June 1, 2024
  3. 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 SiO2oxide, 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.

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  4. Piyawattanametha, Wibool ; Park, Yong-Hwa ; Zappe, Hans (Ed.)
    Recently, two-photon polymerization has been successfully employed to fabricate high-contrast one-dimensional photonic crystals. Using this approach, photonic bandgap reflectivities over 90% have been demonstrated in the infrared spectral range. As a result of this success, modifications to the design are being explored which allow additional tunability of the photonic bandgap. In this paper, a one-dimensional photonic crystal fabricated by two-photon polymerization which has been modified to include mechanical flexures is evaluated. Experimental findings suggest these structures allow mechanically induced spectral shifting of the entire photonic bandgap. These results support the use of one-dimensional photonic crystals fabricated by two-photon polymerization for opto-mechanical applications. 
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    Free, publicly-accessible full text available March 15, 2024
  5. Digonnet, Michel J. ; Jiang, Shibin (Ed.)
    Plasmonic metasurfaces composed of arrays of rectangular metallic bars are well known for their strong optical response in the infrared spectral range. In this study, we explore the polarization sensitivity of plasmonic metasurfaces for encoding information. The polarization-sensitive optical response depends strongly on the orientation of the metallic bars allowing the encoding of information into the metasurface. Here we demonstrate that a 2-dimensional polarization encoded metasurface can be obtained by using mask-less two-photon polymerization techniques. This novel approach for the fabrication of plasmonic metasurfaces enables the rapid prototyping and adaptation of polarization sensitive metasurfaces for the encoding of multiplexed images. 
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    Free, publicly-accessible full text available March 14, 2024