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 (TTz2+) and blue (TTz0) states were extracted from a numerical wavelength-by-wavelength inversion of the experimental data. The extracted dielectric functions are in good agreement with a Kramers-Kronig 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.
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.
One-dimensional photonic crystals have been frequently used as optical filters and in sensing technology due to their ability to induce highly reflective photonic bandgaps. Conventionally, at least two materials are required to create the necessary dielectric contrast for photonic bandgaps to form. Recently, one-dimensional photonic crystals fabricated by two-photon polymerization have demonstrated the ability to induce photonic bandgaps with reflectances over 90%. Using this fabrication approach, dielectric contrast is achieved by altering the density of adjacent layers from a single photo-sensitive polymer. The success of this technique has led to the development of design modifications which allow additional spectral control of the photonic bandgap. In this study, we combine these concepts to develop a one-dimensional photonic crystal which includes a mechanical defect for the first time. Mechanical control of this defect allows for the presence of the transmissive defect mode to be actively shifted in and out of the photonic bandgap. The fabrication of this structure as well as its characterization is reported and discussed. The results of this study further support the use of one-dimensional photonic crystals in opto-mechanical applications where switchable narrow transmission bands are desired.
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.
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.
Mechanical tuning of defect modes in a polymer-based one-dimensional photonic crystal was demonstrated for the terahertz (THz) spectral range. A sharp defect mode in the photonic bandgap was achieved by symmetrically enclosing a defect layer with two identical pairs of alternating compact and low-density layers. By adjusting the thickness of the defect layer, the spectral position of the defect mode within the photonic bandgap was easily controlled. Normal incidence transmission spectroscopy in a spectral range from 82 to 125 GHz was used to determine the THz spectral response for different defect layer thicknesses. The transmission data were analyzed using stratified optical layer model calculations. Spectral shift of the center frequency of the narrow transmission peak within a distinct photonic bandgap was observed in the experimental transmission spectra. The shift was achieved by mechanical tuning of the defect layer thickness. A good agreement between the relevant model parameters and the corresponding design parameters was found.
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