Multi-Wavelength Optical Patterning for Multiscale Materials Design

Reversible Sensing Technologies Using Upcycled TPEE: Crafting pH and Light Responsive Materials towards Sustainable Monitoring

Multiresponsive materials with reversible and durable characteristics are indispensable because of their promising applications in environmental change detections. To fabricate multiresponsive materials in mass production, however, complex reactions and impractical situations are often involved. Herein, a dual responsive (light and pH) spiropyran-based smart sensor fabricated by a simple layer-by-layer (LbL) assembly process from upcycled thermoplastic polyester elastomer (TPEE) materials derived from recycled polyethylene terephthalate (r-PET) is proposed. Positively charged chitosan solutions and negatively charged merocyanine-COOH (MC-COOH) solutions are employed in the LbL assembly technique, forming the chitosan-spiropyran deposited TPEE (TPEE-CH-SP) film. Upon UV irradiation, the spiropyran-COOH (SP-COOH) molecules on the TPEE-CH-SP film undergo the ring-opening isomerization, along with an apparent color change from colorless to purple, to transform into the MC-COOH molecules. By further exposing the TPEE-CH-MC film to hydrogen chloride (HCl) and nitric acid (HNO3) vapors, the MC-COOH molecules can be transformed into protonated merocyanine-COOH (MCH-COOH) with the simultaneous color change from purple to yellow.

Gradient polarization volume grating with wide angular bandwidth for augmented reality

Angular bandwidth, which is critical to field-of-view, plays important role in diffractive optical waveguide augmented reality display. However, design and fabrication of large angular bandwidth is still a challenge. Herein, we demonstrate a liquid crystal reflective gradient polarization volume grating with three-dimensional gradient periodic structure for waveguide near-eye display. Two-beam polarization interference with special designed periodic gradient photomask are applied to chiral-dopant reactive mesogens doped with ultraviolet dye for generating gradient three-dimensional configuration of liquid crystals, resulting in gradient polarization volume grating with extended angle bandwidth of 61° while keeping 80% diffraction efficiency, with peak efficiency near 100%. The proposed gradient polarization volume grating provides an effective method to broaden the angular bandwidth in waveguide for wide field-of-view augmented reality display.

Diffractive Refractometer Based on Scalar Theory

The measurement of the refractive index typically requires the use of optical ellipsometry which, although potentially very accurate, is extremely sensitive to the structural properties of the sample and its theoretical modeling, and typically requires specialized expertise to obtain reliable output data. Here, we propose a simple diffractive method for the measurement of the refractive index of homogenous solid thin films, which requires only the structuring of the surface of the material to be measured with the profile of a diffraction grating. The refractive index of an exemplary soft-moldable material is successfully estimated over a wide wavelength range by simply incorporating the measured topography and diffraction efficiency of the grating into a convenient scalar theory-based diffraction model. Without the need for specialized expertise and equipment, the method can serve as a simple and widely accessible optical characterization of materials useful in material science and photonics applications.

Biomimetic macroscopic hierarchical moire gratings

Large-scale hierarchical macroscopic moire gratings resembling the surface structure of Peruvian lily flower petals are fabricated on azobenzene molecular glass thin films using a Lloyd's mirror interferometer. It is shown that nanostructured linear and crossed moire gratings can be made with pitch values reaching a few millimeters. Also, using atomic force microscopy, scanning electron microscopy, optical microscopy, and surface profilometry techniques, it is shown that the obtained moire gratings have two-fold or three-fold hierarchical structures fabricated using a simple all optical technique.