Metasurfaces have seen a great evolution over the last few years, demonstrating a high degree of control over the amplitude, phase, polarization, and spectral properties of reflected or transmitted electromagnetic waves. Nevertheless, the inherent limitation of static metasurface realizations, which cannot be controlled after their fabrication, engages an ongoing pursuit for reconfigurable metasurfaces with profound tunability. In this paper, we mitigate this grand challenge by demonstrating a new method for free-space rapid optical tunability and modulation, utilizing a planar aluminum nanodisk metasurface coated with indium tin oxide (ITO) on a thin film of lithium niobate (LiNbO) with a chromium/gold (Cr/Au) substrate. Resonance coupling gives rise to an enhanced, confined electromagnetic field residing in the thin film, leading to a narrow and high contrast dip in reflectance of around 1.55 μm. The precise spectral position of this resonance is tuned using the electro-optic Pockels effect by applying an electric bias voltage across the thin film of LiNbO. By doing so, we show that we can likewise modulate the optical reflectance from the metasurface around a wavelength of 1.54 μm. Following that, we experimentally demonstrate a free-space, planar optical modulator with a modulation depth of 40%. The device paves the way for the integration of metasurfaces in applications requiring tunable optical components such as tunable displays, spatial light modulators for advanced imaging, free-space communication, beam scanning LIDARs with no moving parts, and more.
Volumetric imaging with high spatiotemporal resolution is of utmost importance for various applications ranging from aerospace and defense to real-time imaging of dynamic biological processes. To facilitate three-dimensional sectioning, current technology relies on mechanisms to reject light from adjacent out-of-focus planes either spatially or by other means. Yet, the combination of rapid acquisition time and high axial resolution is still elusive, motivating a persistent pursuit for emerging imaging approaches. Here we introduce and experimentally demonstrate a concept named spectrally gated microscopy (SGM), which enables a single-shot interrogation over the full axial dimension while maintaining a submicron sectioning resolution. SGM utilizes two important features enabled by flat optics (i.e., metalenses or diffractive lenses), namely, a short focal length and strong chromatic aberrations. Using SGM we demonstrate three-dimensional imaging of millimeter-scale samples while scanning only the lateral dimension, presenting a significant advantage over state-of-the-art technology.
Surface water pollution is one of the serious environmental problems in urban centers ofNepal due to the discharge of untreated wastewater. Almost all conventional type wastewaterplants are not functioning well and practically not sustainable due to lack of regularmaintenance and high operation cost. To overcome this, Constructed Wetland (CW)technology for wastewater treatment arises as alternative technology in Nepal. Now, there are12 sub-surface flow CW systems in operation all over the country.This study aims to checking the efficiency and performance evaluation of three CW located atvarious locations in Nepal. The performance evaluation was conducted through collection ofwastewater samples from inlet and outlet sources of treatment plants and measuringsignificant water qualities determining physical and chemical parameters such as BiochemicalOxygen Demand (BOD), Chemical Oxygen Demand (COD), Hydrogen ion concentration(pH), Conductivity, Phosphorus, Total Suspended Solids (TSS), Total Dissolved Solids (TDS)and Total Solids (TS).The CW systems were found efficiently removing and reducing different pollutionparameters. Performance of CW system were excellent for Kathmandu University (KU) andMalpi International School (Malpi) where the efficiency levels ranged between 82% to 96%for BOD, 68% to 85% for COD, 91 % to 99% for TSS, 60% to 83% for TDS and for TS 84%to 92%. The performance efficiency was relatively lower for Thimi Community ScaleWastewater Treatment Plant (Thimi) where the efficiency levels was 56% for BOD, 64% forCOD, 17% for Conductivity, 88% for TSS, 59% for TDS and 80% for TS. The results showthat, the CW systems are useful and efficient for waste water treatment in growing urbanareas. They are cost effective and easy to maintain. It is recommended that CW system couldbe replicate in other growing urban areas.
We demonstrate a tunable metasurface made of aluminum nanodisk array coated with ITO on a thin film of lithium niobate. A spectral resonant shift of few nanometers and modulation contrast of ~40% are observed.
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