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Tremendous increase in anthropogenic activities and natural disasters have created long term negative impacts to the crop productivity as well as on our ecosystem. In the debate regarding the ongoing ecosystem fluctuations, there is a need to explore an efficient, cost-effective, target-oriented and less manpower-based technologies for sustainable development. Microbial engineering provides a better solution for the growth of a healthy environment and higher agricultural productivity over the existing methods and resolved the challenges worldwide related to development of sustainable agriculture and greener ecosystems. In recent years, researchers are working on the development of different advanced microbial engineering strategies such as gene editing, CRISPR/Cas9, and RNAi to enhance the potential of microorganisms towards higher plant productivity and degradation of pollutants. The present review focused on the potential applications of genetically engineered microbial inoculants for sustainable agriculture and greener ecosystem development.

Abstract Orbital current, defined as the orbital character of Bloch states in solids, can travel with larger coherence length through a broader range of materials than its spin counterpart, facilitating a robust, higher density and energy efficient information transmission. Hence, active control of orbital transport plays a pivotal role in the progress of the evolving field of quantum information technology. Unlike spin angular momentum, orbital angular momentum couples to phonon angular momentum efficiently via orbital-crystal momentum (L-k) coupling, allowing us to control orbital transport through crystal field potential mediated angular momentum transfer. Here, leveraging the orbital dependant efficient L-k coupling, we have experimentally demonstrated the active control of orbital current velocity in Ni/Pt heterostructure. We observe terahertz emission from Ni/Pt heterostructure via long-range ballistic orbital transport, as evidenced by the delay, and chirping in the emitted THz pulse correlating with increased Pt thickness. Additionally, we also have identified a critical energy density required to overcome collisions in orbital transport, enabling a swifter flow of orbital current. Femtosecond light driven active control of the ballistic orbital transport lays the foundation for the development of dynamic optorbitronics for transmitting information over extended distance.

Abstract Topological slow light exhibits potential to achieve stopped light by virtue of its widely known robust and non-reciprocal behaviours. Conventional approach for achieving topological slow light often involves flat-band engineering without disentangling the underlying physical mechanism. Here, we unveil the presence of counter-propagating waves within valley kink states as the distinctive hallmark of the slow light topological photonic waveguides. These counter-propagating waves, supported by topological vortices along glide-symmetric interface, provide significant flexibility for controlling the slowness of light. We tune the group velocity of light by changing the spatial separation between vortices adjacent to the glide-symmetric interface. We also dynamically control the group delay by introducing a non-Hermitian defect using photoexcitation to adjust the relative strength of the counter-propagating waves. This study introduces active slow light topological photonic device on a silicon chip, opening new horizons for topological photon transport through defects, topological light-matter interactions, nonlinear topological photonics, and topological quantum photonics.

As sugarcane molasses is converted into ethanol, a sizable volume of effluent with high biochemical oxygen demand (BOD) and chemical oxygen demand(COD) is generated. This effluent contains melanoidin. Melanodin is a chemical broken down by certain bacteria and can produce peroxidases, phenoxidases, laccases, and mono- and dioxygenases. The primary function of these bacteria is to break down complex hydrocarbons, including aromatics such as coloring pigments. This study aimed to identify melanoidin-decolorizing microorganisms in natural resources that are thermally resistant and have the potential to be used in industrial-scale distillery treatment for effluent applications. A total of 55 distinct isolates were tested on a solid medium, including molasses pigments. Three thermotolerant bacterial isolates were identified as melanoidin-decolorizing agents: Bacillus nitratireducens (B2), Bacillus paramycoides (B1), and Brucellatritici (B3). These isolates under went additional optimization for decolorization under various physicochemical and nutritional conditions. At 40°C, B. nitratireducens (B2) exhibited the highest degree of decolorization (86%) among the three species while using 0.5% glucose(w/v), 0.5% peptone(w/v), 0.05% MgSO4, and 0.01% KH2PO4 at a pH of 6.0 over 40 h of incubation under static conditions. In submerged fermentation, the B2 strain of B.nitratireducens can withstand higher temperatures and requires only a small amount of carbon (0.5%, [w/v]) and nitrogen sources (0.5%, [w/v]). Therefore, it is feasible to use melanoidin on an industrial scale to decolorize distilled effluents.

Anthropogenic activities and increasing human population has led to one of the major global problems of heavy metal contamination in ecosystems and to the generation of a huge amount of waste material biomass. Hexavalent chromium [Cr(VI)] is the major contaminant introduced by various industrial effluents and activities into the ecosystem. Cr(VI) is a known mutagen and carcinogen with numerous detrimental effects on the health of humans, plants, and animals, jeopardizing the balance of ecosystems. Therefore, the remediation of such a hazardous toxic metal pollutant from the environment is necessary. Various physical and chemical methods are available for the sequestration of toxic metals. However, adsorption is recognized as a more efficient technology for Cr(VI) remediation. Adsorption by utilizing waste material biomass as adsorbents is a sustainable approach in remediating hazardous pollutants, thus serving the dual purpose of remediating Cr(VI) and exploiting waste material biomass in an eco- friendly manner. Agricultural biomass, industrial residues, forest residues, and food waste are the primary waste material biomass that could be employed, with different strategies, for the efficient sequestration of toxic Cr(VI). This review focuses on the use of diverse waste biomass, such as industrial and agricultural by-products, for the effective remediation of Cr(VI) from aqueous solutions. The review also focuses on the operational conditions that improve Cr(VI) remediation, describes the efficacy of various biomass materials and modifications, and assesses the general sustainability of these approaches to reducing Cr(VI) pollution.

Plant-microbe interactions are pivotal for ecosystem dynamics and sustainable agriculture, and are influenced by various factors, such as host characteristics, environmental conditions, and human activities. Omics technologies, including genomics, transcriptomics, proteomics, and metabolomics, have revolutionized our understanding of these interactions. Genomics elucidates key genes, transcriptomics reveals gene expression dynamics, proteomics identifies essential proteins, and metabolomics profiles small molecules, thereby offering a holistic perspective. This review synthesizes diverse microbial-plant interactions, showcasing the application of omics in understanding mechanisms, such as nitrogen fixation, systemic resistance induction, mycorrhizal association, and pathogen-host interactions. Despite the challenges of data integration and ethical considerations, omics approaches promise advancements in precision intervention and resilient agricultural practices. Future research should address data integration challenges, enhance omics technology resolution, explore epigenomics, and understand plant-microbe dynamics under diverse conditions. In conclusion, omics technologies hold immense promise for optimizing agricultural strategies and fortifying resilient plant-microbe alliances, paving the way for sustainable agriculture and environmental stewardship.

Abstract Surface enhanced Resonance Raman spectroscopy (SERRS) is a powerful technique for enhancing Raman spectra by matching the laser excitation wavelength with the plasmonic resonance and the absorption peak of biomolecules. Here, we propose a tunable Tamm plasmon polariton (TPP) cavity based on a metal on distributed Bragg reflector (DBR) as a scalable sensing platform for SERRS. We develop a gold film-coated ultralow-loss phase change material (Sb2S3) based DBR, which exhibits continuously tunable TPP resonances in the optical wavelengths. We demonstrate SERRS by matching the TPP resonance with the absorption peak of the chromophore molecule at 785 nm wavelength. We use this platform to detect cardiac Troponin I protein (cTnI), a biomarker for early diagnosis of cardiovascular disease, achieving a detection limit of 380 fM. This scalable substrate shows great promise as a next-generation tunable biosensing platform for detecting disease biomarkers in body fluids for routine real-time clinical diagnosis.

Intense terahertz (THz) radiation in free space has immense potential for regulating material state, accelerating electrons, producing biological effects, and so on. However, the high cost and challenges involved in constructing strong-field THz sources have limited their developments, making it difficult for the potential applications of strong-field THz radiation to be widely adopted. Spintronic THz emitters (STEs) with numerous merits such as high efficiency, ultrabroadband, ease of integration, and low cost have become ubiquitous, but the majority of these emitters require stable operation in the presence of external magnets, limiting their applications, particularly in generating strong fields that necessitate large-sized samples. Here, we demonstrate the feasibility of generating strong-field THz radiation in 4-inch antiferromagnetic material–ferromagnetic metal (IrMn3 [2 nm]/Co20Fe60B20 [2 nm]/W [2 nm]) without external magnetic field driving. Under the excitation of a Ti:sapphire femtosecond laser amplifier with a 35-fs pulse duration and a 1-kHz repetition rate, we obtain strong-field THz radiation from our STEs with a pulse duration of ~110 fs, and a spectrum covering up to ~10 THz. Further scaling up the pump laser energy up to 55 mJ with a pulse duration of ~20 fs and a repetition rate of 100 Hz provided by the Synergetic Extreme Condition User Facility, the radiated THz electric field strength from the external-magnetic-free 4-inch STEs can exceed 242 kV/cm with a pulse duration of ~230 fs, a spectrum covering up to ~14 THz, and a single pulse energy of 8.6 nJ measured by a calibrated pyroelectric detector. Our demonstrated external-magnetic-field-free high-field STEs have some unique applications such as producing sub-cycle ultrashort strong THz fields in huge size emitters under the excitation of high-energy light sources, accelerating the development of THz science and applications.

Abstract Non-radiative bound states in the continuum (BICs) allow construction of resonant cavities with confined electromagnetic energy and high-quality (Q) factors. However, the sharp decay of the Q factor in the momentum space limits their usefulness for device applications. Here we demonstrate an approach to achieve sustainable ultrahigh Q factors by engineering Brillouin zone folding-induced BICs (BZF-BICs). All the guided modes are folded into the light cone through periodic perturbation that leads to the emergence of BZF-BICs possessing ultrahigh Q factors throughout the large, tunable momentum space. Unlike conventional BICs, BZF-BICs show perturbation-dependent dramatic enhancement of the Q factor in the entire momentum space and are robust against structural disorders. Our work provides a unique design path for BZF-BIC-based silicon metasurface cavities with extreme robustness against disorder while sustaining ultrahigh Q factors, offering potential applications in terahertz devices, nonlinear optics, quantum computing, and photonic integrated circuits.

6G communication requires high-speed and advanced functionalities on-chip. Here the authors demonstrate broadband phototunable topological waveguide and demultiplexing chip with record single-channel 160 Gbit/s communication link and excellent channel isolation for 300 GHz band.

A novel laboratory model was designed to study the arsenic (As) biotransformation potential of the microalgae Chlorella vulgaris and Nannochloropsis sp. and the cyanobacterium Anabaena doliolum. The Algae were treated under different concentrations of As(III) to check their growth, toxicity optimization, and volatilization potential. The results revealed that the alga Nannochloropsis sp. was better adopted in term of growth rate and biomass than C. vulgaris and A. doliolum. Algae grown under an As(III) environment can tolerate up to 200 μM As(III) with moderate toxicity impact. Further, the present study revealed the biotransformation capacity of the algae A. doliolum, Nannochloropsis sp., and Chlorella vulgaris. The microalga Nannochloropsis sp. volatilized a large maximum amount of As (4,393 ng), followed by C. vulgaris (4382.75 ng) and A. doliolum (2687.21 ng) after 21 days. The present study showed that As(III) stressed algae-conferred resistance and provided tolerance through high production of glutathione content and As-GSH chemistry inside cells. Thus, the biotransformation potential of algae may contribute to As reduction, biogeochemistry, and detoxification at a large scale.

Spintronic terahertz (THz) emitters are a class of magnetic heterostructure where femtosecond laser excitations generate THz radiation emission. While they have great potential, electric field control of spintronic emitter remains a challenge. Here, by combining a spintronic emitter with a piezoelectric substrate, Agarwal et al. demonstrate electric field control of THz emission through induced piezostrain.

Toxic wastes like heavy metals and dyes are released into the environment as a direct result of industrialization and technological progress. The biosorption of contaminants utilizes a variety of biomaterials. Biosorbents can adsorb toxic pollutants on their surface through various mechanisms like complexation, precipitation, etc. The quantity of sorption sites that are accessible on the surface of the biosorbent affects its effectiveness. Biosorption’s low cost, high efficiency, lack of nutrient requirements, and ability to regenerate the biosorbent are its main advantages over other treatment methods. Optimization of environmental conditions like temperature, pH, nutrient availability, and other factors is a prerequisite to achieving optimal biosorbent performance. Recent strategies include nanomaterials, genetic engineering, and biofilm-based remediation for various types of pollutants. The removal of hazardous dyes and heavy metals from wastewater using biosorbents is a strategy that is both efficient and sustainable. This review provides a perspective on the existing literature and brings it up-to-date by including the latest research and findings in the field.

The presence of dye in wastewater causes substantial threats to the environment, and has negative impacts not only on human health but also on the health of other organisms that are part of the ecosystem. Because of the increase in textile manufacturing, the inhabitants of the area, along with other species, are subjected to the potentially hazardous consequences of wastewater discharge from textile and industrial manufacturing. Different types of dyes emanating from textile wastewater have adverse effects on the aquatic environment. Various methods including physical, chemical, and biological strategies are applied in order to reduce the amount of dye pollution in the environment. The development of economical, ecologically acceptable, and efficient strategies for treating dye-containing wastewater is necessary. It has been shown that microbial communities have significant potential for the remediation of hazardous dyes in an environmentally friendly manner. In order to improve the efficacy of dye remediation, numerous cutting-edge strategies, including those based on nanotechnology, microbial biosorbents, bioreactor technology, microbial fuel cells, and genetic engineering, have been utilized. This article addresses the latest developments in physical, chemical, eco-friendly biological and advanced strategies for the efficient mitigation of dye pollution in the environment, along with the related challenges.

Context: Serum complement proteins and autoantibodies play an important role in the pathogenesis and diagnosis of systemic lupus erythematosus (SLE). Abnormalities in various immunoglobulin levels are described in patients of SLE. Aims: To study the spectrum of clinical manifestations and measure the serum levels of complement C3, complement C4, autoantibodies and immunoglobulin G (IgG) in patients of SLE and compare with healthy controls. Settings and Design: The present study is a prospective hospital-based observational study conducted between May 2014 and December 2018. Statistical Analysis Used: Unpaired t-test was used to compare the mean values between the SLE patients and healthy controls. Material and Methods: A total of 100 cases of SLE and 100 healthy controls were included in the study. The clinical data were retrieved. Serum antinuclear antibody, anti-ds DNA antibody, and anti-Smith antibody levels, and complements C3, C4 and IgG were measured. Results: Arthritis (89%) and anaemia (65%) were two common clinical presentations. The low complement C3 levels and C4 were detected in 64 and 62% of the SLE patients. Serum IgG was increased in 41% of the patients. A reduced level of IgG was detected in 6% of the patients. Conclusion: Primary care physicians should be aware of the clinical and serological manifestations of SLE as early detection will reduce end-organ damage. Autoantibody testing and complement testing should be done in all suspected cases. This study showed a significantly reduced C3 and C4 and elevated IgG in many cases of SLE as compared to control. Hypogammaglobulinemia was also present in a minority of the cases.

Manipulating photon dynamics is becoming increasingly important especially for quantum optics applications. In this work, the authors provide a mechanism that functions as a ‘photon brake’ which relies on the concept of temporal loss boundary to manipulate the dynamics of cavity photons.

Jackfruit is a potential natural resource for many valuable biomaterials. The wastes from jackfruit are rich in carbohydrate, proteins, fats and phytochemicals. These wastes can be used as feedstock for the development of various bioproducts. The pretreatment strategies like biological, physical and chemical methods are being used for effective valorization of fruit wastes into value added products, like bioethanol, biogas, bioplastics, feeds, functional food additives, and other useful compounds. Bioenergy production from such renewable resources is an eco-friendly and cost-effective alternative option of fuels, unlike fossil fuels. The efficient bioconversion of fruit waste into useful biomaterials is facilitated by microbial fermentation process. Also, jackfruit peel is applied in the pollution abatement by remediation of dyes color from contaminated aquatic environment. Such technology can be used to develop a green economic model for waste utilization. This review addressed the utilization feasibility of jackfruit waste to produce value added products in order to reduce wastes and protect environment in a sustainable way.

The current investigation is the first report of utilization of Aspergillus brasiliensis for the decolorization of melanoidin in distillery effluent. The effluent generated from alcohol distilleries is one of the most complex wastewater with a high biological oxygen demand (BOD) and other organic, inorganic, and toxic constituents. The effluent contains melanoidin, a dark brown compound, which is difficult to remediate by using conventional technologies. The disposal of spent wash in the natural environment is hazardous and can deteriorate land and water resources. The decolorization of spent wash through physical and chemical methods remains unsuitable, and the only alternative to decolorize spent wash is biological treatment. In the current study, three fungal strains were isolated from the distillery waste and screened for their ability to decolorize melanoidin.The isolate RS2 exhibited maximum decolorization of 83% and was identified as Aspergillus brasiliensis. Its optimum growth temperature was 37EC, and the maximum efficiency was recorded after 120 h of incubation. Nutritional sources were investigated for the fungi showing the maximum decolorization of melanoidin, and starch and peptone were found to be the best carbon and nitrogen sources, respectively. At 1.5% starch concentration and 1.5% peptone concentration, the decolorization level attained was 87.45% and 88.74%, respectively. A. brasiliensis exhibited a high potential to decolorize melanoidin. The decolorization percentage was high, which makes this fungus a potential candidate for use at the industrial scale for the bioremediation of spent wash.

Abstract Lipases are very versatile enzymes, and produced the attention of the several industrial processes. Lipase can be achieved from several sources, animal, vegetable, and microbiological. The uses of microbial lipase market is estimated to be USD 425.0 Million in 2018 and it is projected to reach USD 590.2 Million by 2023, growing at a CAGR of 6.8% from 2018. Microbial lipases (EC 3.1.1.3) catalyze the hydrolysis of long chain triglycerides. The microbial origins of lipase enzymes are logically dynamic and proficient also have an extensive range of industrial uses with the manufacturing of altered molecules. The unique lipase (triacylglycerol acyl hydrolase) enzymes catalyzed the hydrolysis, esterification and alcoholysis reactions. Immobilization has made the use of microbial lipases accomplish its best performance and hence suitable for several reactions and need to enhance aroma to the immobilization processes. Immobilized enzymes depend on the immobilization technique and the carrier type. The choice of the carrier concerns usually the biocompatibility, chemical and thermal stability, and insolubility under reaction conditions, capability of easy rejuvenation and reusability, as well as cost proficiency. Bacillus spp., Achromobacter spp., Alcaligenes spp., Arthrobacter spp., Pseudomonos spp., of bacteria and Penicillium spp., Fusarium spp., Aspergillus spp., of fungi are screened large scale for lipase production. Lipases as multipurpose biological catalyst has given a favorable vision in meeting the needs for several industries such as biodiesel, foods and drinks, leather, textile, detergents, pharmaceuticals and medicals. This review represents a discussion on microbial sources of lipases, immobilization methods increased productivity at market profitability and reduce logistical liability on the environment and user.

The enzymatic saccharification of sugarcane bagasse was significantly increased by alkali pretreatment under mild conditions. The effectiveness of different concentrations of alkali and acid pretreatment of sugarcane bagasse for improving the enzymatic saccharification of lignocellulose has been evaluated. The sugarcane bagasse was characterized to contain 39.52% celluloses, 25.63% hemicelluloses, and 30.36% lignin. After that, sugarcane bagasse was pretreated with 5 and 10% of H2SO4 and NaOH at 121°C for 60 min. FTIR, XRD, and SEM analyses also showed significant molecular and surface structure changes of the sugarcane bagasse with 10% NaOH. Maximum saccharification was 489.5 mg/g from 10% NaOH pretreatment followed by 322.75, 301.25, and 276.6 mg/g from 10% H2SO4, 5% NaOH, and 5% H2SO4, respectively, which were 55.1, 32.0, 27.1, and 20.6 times higher than the that of the control. Cellulase and xylanase produced by Pseudomonas sp. CVB-10 (MK443365) and Bacillus paramycoides T4 (MN370035) were used to hydrolyze the pretreated bagasse, and the optimal condition was determined to be 30 h of the enzymatic reaction with the 3:1 ratio of enzymes under the temperature of 55°C, pH 5.0, and substrate concentration of 3%, leading to celluloses and hemicelluloses conversion in the enzymatic hydrolysis/saccharification that is more proficient.

The agricultural sector generates a significant amount of waste, the majority of which is not productively used and is becoming a danger to both world health and the environment. Because of the promising relevance of agro-residues in the agri-food-pharma sectors, various bioproducts and novel biologically active molecules are produced through valorization techniques. Valorization of agro-wastes involves physical, chemical, and biological, including green, pretreatment methods. Bioactives and bioproducts development from agro-wastes has been widely researched in recent years. Nanocapsules are now used to increase the efficacy of bioactive molecules in food applications. This review addresses various agri-waste valorization methods, value-added bioproducts, the recovery of bioactive compounds, and their uses. Moreover, it also covers the present status of bioactive micro- and nanoencapsulation strategies and their applications.

Abstract Space‐time wave packets are electromagnetic waves with strong correlations between their spatial and temporal degrees of freedom. These wave packets have gained much attention for fundamental properties like propagation invariance and user‐designed group velocities, and for potential applications like optical microscopy, micromanipulation, and laser micromachining. Here, free‐electron radiation is presented as a natural and versatile source of space‐time wave packets that are ultra‐broadband and highly tunable in frequency. For instance, ab initio theory and numerical simulations show that the intensity profile of space‐time wave packets from Smith‐Purcell radiation can be directly tailored through the grating properties, as well as the velocity and shape of the electron bunches. The result of this work indicates a viable way of generating space‐time wave packets at exotic frequencies such as the terahertz and X‐ray regimes, potentially paving the way toward new methods of shaping electromagnetic wave packets through free‐electron radiation.

The present study was conducted to examine the photosynthetic performance, nutrient status and lipid yield in microalgae Chlorococcum humicola and Chlorella vulgaris under different durations of UV-B exposure (1/2 h, 1 h, 2 h, 3 h and 4 h). Results revealed that UV-B reduces the photosynthetic performance of photosystem II by altering photosynthetic performance index (Pi ABS), maximum quantum yield (Fv/Fm), net closing rate of reaction centre (Mo), trapping flux (TRo/RC) and effective antenna size with their respective control. Scanning Electron Microscopy (SEM) exhibited variegated structure and increased cell size by ~15–65% which was more pronounced in the case of C. humicola at 4 h of UV-B. The Energy Dispersive Spectroscopy (EDS) data showed that the content of microelements (C, O, Na, and K) in terms of atomic weight % was found to be significantly increased in C. vulgaris while with C. humicola, it was restricted to carbon (C) only. Further, the high antioxidant (ascorbic acid, cysteine and proline) potential and carotenoid/chl a photoprotection response reflects protection against UV-B in the both algae. In the case of lipid, comparative greater increase in cell size of C. humicola correlated with high lipid yield as compare to C. vulgaris at 2 h of UV-B could be employed in the production of biofuel in sustainable manner. Thus, algae C. humicola could be a best alternative feed stock of lipid and biofuel production in the area receiving high solar radiation.

A toroidal dipole is a new class of electromagnetic excitations and are different from traditional electric and magnetic dipoles. Toroidal dipoles are described by the poloidal currents flowing on the surface of torus and have opened a new route to control radiative losses via near field coupling mechanism or radiation cancellation approach in the unit cell of metasurface. Radiative loss engineering in metamaterials is one of the most fundamental requirements to gauge the suitability of a metaphotonic device for a specific on-demand application. Here, we discuss strategies to excite toroidal dipolar modes in a planar metasurface which were initially thought to exist only in three-dimensional (3D) arrangements. Two dimensional (2D) toroidal metasurfaces are conceptual simplification of 3D toroid configurations, which pose fabrication challenges at micro-nanoscales. We further discuss the destructive interference between electric and toroidal dipoles to realize non-radiating modes in the form of an anapole excitation that fulfills the requirement for the excitation of extremely large quality factor resonances. Overall, the intriguing features of a toroidal dipole could have significant implications on the design of resonant metamaterials that are important for the development of low-loss sensors, modulators, filters, and efficient cavities for strong light matter interactions.

Here, the authors demonstrate excitation and active tuning of sharp Fano resonances in a MEMS reconfigurable metasurface possessing multiple-input-output states. They realize XOR, XNOR, NOT and NAND logic gate operations by using two independently controllable electrical inputs and an optical readout using terahertz beam.

Abstract The observation of Fano resonance phenomena is universal across several branches of physics. Photonics is one of the most important areas of physics that mainly deals with the control of light propagation and localization through its interaction with natural and artificially engineered media. In an era of miniaturization, manipulation of light at micro-nanoscales has assumed unprecedented significance due to its potential to satisfy the mankind with disruptive future technologies. In this work, we present our study on the universality of high quality factor Fano resonances in planar metamaterials across terahertz and infrared parts of the electromagnetic spectrum. The narrow linewidth asymmetric Fano resonant metamaterials have tremendous potential to find applications in micro-nanoscale flat lasers, sensors, and ultra-resolution spectrometers.

Optical sensors generally rely on abrupt phase changes to detect the presence of an analyte, but oftentimes they require complex nanostructures. Here, Sreekanth et al. use a simple asymmetric thin-film multilayer stack to demonstrate a point of darkness and phase singularity to develop a sensitive biosensor.

Abstract Excitation and manipulation of surface plasmons (SPs) are essential in developing cutting-edge plasmonic devices for medical diagnostics, biochemical spectroscopy and communications. The most common approach involves designing an array of periodic slits or grating apertures that enables coupling of the incident light to the SP modes. In recent years, plasmonic resonances, including extraordinary optical transmission through periodic arrays, quasicrystals and random aperture arrays, have been investigated in the free space. However, most of the studies have been limited to the far field detection of the transmission resonance. Here, we perform near-field measurements of the SPs on quasicrystal metasurfaces. We discover that the reciprocal vector determines the propagation modes of the SPs in the quasicrystal lattice which can be well explained by the quasi-momentum conservation rule. Our findings demonstrate vast potential in developing plasmonic metasurfaces with unique device functionalities that are controlled by the propagation modes of the SPs in quasicrystals.

Optical chirality is central to many industrial photonic technologies including enantiomer identification, ellipsometry-based tomography, and spin multiplexing in optical communications. However, a substantial chiral response requires a three-dimensional constituent, thereby making the morphology highly complex to realize structural reconfiguration. Moreover, an active reconfiguration demands intense dosage of external stimuli that pose a major limitation for on-chip integration. Here, we report a low bias, electrically programmable synthetic chiral paradigm with a remarkable reconfiguration among levorotatory, dextrorotatory, achiral, and racemic conformations. The switchable optical activity induced by the chiral conformations enables a transmission-type duplex spatial light modulator for terahertz single pixel imaging. The prototype delivers a new strategy towards reconfigurable stereoselective photonic applications and opens up avenues for on-chip programmable chiral devices with tremendous applications in biology, medicine, chemistry, and photonics.

Terahertz (THz) technique has become one of the most promising analytical methods and has been applied in many fields. Attenuated total reflection (ATR) technique applied in THz spectroscopy and imaging has been proven to be superior in functionalities such as modulation, sensing, analyzing, and imaging. Here, we first provide a concise introduction to the principle of ATR, discuss the factors that impact the ATR system, and demonstrate recent advances on THz wave modulation and THz surface plasmon sensing based on the THz-ATR system. Then, applications on THz-ATR spectroscopy and imaging are reviewed. Towards the later part, the advantages and limitations of THz-ATR are summarized, and prospects of modulation, surface plasmon sensing, spectroscopy and imaging are discussed.

Diffraction of light in periodic structures is observed in a variety of systems including atoms, solid state crystals, plasmonic structures, metamaterials, and photonic crystals. In metamaterials, lattice diffraction appears across microwave to optical frequencies due to collective Rayleigh scattering of periodically arranged structures. Light waves diffracted by these periodic structures can be trapped along the metamaterial surface resulting in the excitation of surface lattice resonances, which are mediated by the structural eigenmodes of the metamaterial cavity. This has brought about fascinating opportunities such as lattice-induced transparency, strong nearfield confinement, and resonant field enhancement and line-narrowing of metamaterial structural resonances through lowering of radiative losses. In this review, we describe the mechanisms and implications of metamaterial-engineered surface lattice resonances and lattice-enhanced field confinement in terahertz metamaterials. These universal properties of surface lattice resonances in metamaterials have significant implications for the design of resonant metamaterials, including ultrasensitive sensors, lasers, and slow-light devices across the electromagnetic spectrum.

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We present a review of the different coupling schemes in a planar array of terahertz metamaterials. The gap-to-gap near-field capacitive coupling between split-ring resonators in a unit cell leads to either blue shift or red shift of the fundamental inductive-capacitive (LC) resonance, depending on the position of the split gap. The inductive coupling is enhanced by decreasing the inter resonator distance resulting in strong blue shifts of the LC resonance. We observe the LC resonance tuning only when the split-ring resonators are in close proximity of each other; otherwise, they appear to be uncoupled. Conversely, the higher-order resonances are sensitive to the smallest change in the inter particle distance or split-ring resonator orientation and undergo tremendous resonance line reshaping giving rise to a sharp subradiant resonance mode which produces hot spots useful for sensing applications. Most of the coupling schemes in a metamaterial are based on a near-field effect, though there also exists a mechanism to couple the resonators through the excitation of lowest-order lattice mode which facilitates the long-range radiative or diffractive coupling in the split-ring resonator plane leading to resonance line narrowing of the fundamental as well as the higher order resonance modes.

We report the observation of a nonlinear terahertz response of split-ring resonator arrays made of high-temperature superconducting films. Intensity-dependent transmission measurements indicate that the resonance strength decreases dramatically (i.e. transient bleaching) and the resonance frequency shifts as the intensity is increased. Pump–probe measurements confirm this behaviour and reveal dynamics on the few-picosecond timescale.