UV-enhanced photorefractive response rate in a thin-film lithium niobate microdisk.

The photorefractive (PR) effect plays a critical role in emerging photonic technologies, including dynamic volume holography and on-chip all-optical functionalities. Nevertheless, its slow response rate has posed a significant obstacle to its practical application. Here, we experimentally demonstrate the enhancement of the PR response rate in a high-Q thin-film lithium niobate (TFLN) microdisk under UV light irradiation. At an irradiation intensity of 30 mW/cm2, the PR effect achieves a high response bandwidth of approximately 256 kHz. By employing this UV-assisted PR effect, we have achieved rapid laser-cavity locking and self-stabilization, where perturbations are automatically compensated. This technique paves the way toward real-time dynamic holography, editable photonic devices on a lithium niobate platform, and high-speed all-optical information processing.

Poling-assisted hydrofluoric acid wet etching of thin-film lithium niobate.

Thin-film lithium niobate (TFLN) has been extensively investigated for a wide range of applications due to continuous advancements in its fabrication methods. The recent emergence of high-fidelity ferroelectric domain poling of TFLN provides an opportunity for achieving a precise pattern control of ferroelectric domains and a subsequent pattern transfer to the TFLN layer using hydrofluoric acid (HF). In this work, we present, to the best of our knowledge, the first demonstration of z-cut TFLN microdisks using a poling-assisted HF wet etching approach. By applying intense electric fields, we are able to induce a domain inversion in the TFLN with a designed microdisk pattern. A HF solution is subsequently utilized to transfer the inverted domain pattern to the TFLN layer with the selective etching of -z LN, ultimately revealing the microdisks.

Distinct spatiotemporal succession of bacterial generalists and specialists in the lacustrine plastisphere.

The assembly processes of generalists and specialists and their driving mechanisms during spatiotemporal succession is a central issue in microbial ecology but a poorly researched subject in the plastisphere. We investigated the composition variation, spatiotemporal succession, and assembly processes of bacterial generalists and specialists in the plastisphere, including non-biodegradable (NBMPs) and biodegradable microplastics (BMPs). Although the composition of generalists and specialists on NBMPs differed from that of BMPs, colonization time mainly mediated the composition variation. The relative abundance of generalists and the relative contribution of species replacement were initially increased and then decreased with colonization time, while the specialists initially decreased and then increased. Besides, the richness differences also affected the composition variation of generalists and specialists in the plastisphere, and the generalists were more susceptible to richness differences than corresponding specialists. Furthermore, the assembly of generalists in the plastisphere was dominated by deterministic processes, while stochastic processes dominated the assembly of specialists. The network stability test showed that the community stability of generalists on NBMPs and BMPs was lower than corresponding specialists. Our results suggested that different ecological assembly processes shaped the spatiotemporal succession of bacterial generalists and specialists in the plastisphere, but were less influenced by polymer types.

Abundance and diversity of eukaryotic rather than bacterial community relate closely to the trophic level of urban lakes.

Scientific understanding of biotic effects on the water trophic level is lacking for urban lakes during algal bloom development stage. Based on the Illumina MiSeq sequencing, quantitative polymerase chain reaction (PCR), and multiple statistical analyses, we estimated distribution patterns and ecological roles of planktonic bacteria and eukaryotes in urban lakes during algal bloom development stage (i.e., April, May, and June). Cyanobacteria and Chlorophyta mainly dominated algal blooms. Bacteria exhibited significantly higher absolute abundance and community diversity than eukaryotes, whereas abundance and diversity of eukaryotic rather than bacterial community relate closely to the water trophic level. Multinutrient cycling (MNC) index was significantly correlated with eukaryotic diversity rather than bacterial diversity. Stronger species replacement, broader environmental breadth, and stronger phylogenetic signal were found for eukaryotic community than for bacterial community. In contrast, bacterial community displayed stronger community stability and environmental constraint than eukaryotic community. Stochastic and differentiating processes contributed more to community assemblies of bacteria and eukaryotes. Our results emphasized that a strong linkage between planktonic diversity and MNC ensured a close relationship between planktonic diversity and the water trophic level of urban lakes. Our findings could be useful to guide the formulation and implementation of environmental lake protection measures.

Multi-color complex spatial light modulation with a single digital micromirror device.

Spatial light modulators enabling complex light field manipulation has opened up many opportunities in biomedical imaging, holographic display, and adaptive optics. However, traditional spatial light modulators do not allow multi-color operations simultaneously due to their physical constraints, while multi-color modulations are highly desirable in many applications. To overcome this limitation, we demonstrate a multi-color spatial complex light field modulation with a single binary hologram on digital micromirror devices (DMD). This method combines several neighboring micro-mirror pixels into a giant single superpixel, in which the light field's amplitude and phase can be individually determined by internal pixel combinations, and the dynamic range of phase modulation can exceed 2π for the single wavelength. As a result, this extra phase modulation range offers an additional degree of freedom for independent multi-wavelength light modulation. Based on this scheme, multi-color light modulations have been demonstrated in a 2D plane as well as in multiple 3D holographic planes. Moreover, a dual-colored Airy beam has been realized using the same technique. These results bring complex light modulation into a multi-color regime, paving the way for practical applications in information display, imaging, and optical trapping.

Controllable EIT-like mode splitting in a chiral microcavity.

Two coupled resonance modes can lead to exotic transmission spectra due to internal interference processes. Examples include electromagnetically induced transparency (EIT) in atoms and mode splitting in optics. The ability to control individual modes plays a crucial role in controlling such transmission spectra for practical applications. Here we experimentally demonstrate a controllable EIT-like mode splitting in a single microcavity using a double-port excitation. The mode splitting caused by internal coupling between two counter-propagating resonances can be effectively controlled by varying the power of the two inputs, as well as their relative phase. Moreover, the presence of asymmetric scattering in the microcavity leads to chiral behaviors in the mode splitting in the two propagating directions, manifesting itself in terms of a Fano-like resonance mode. These results may offer a compact platform for a tunable device in all-optical information processing.

Stronger Geographic Limitations Shape a Rapid Turnover and Potentially Highly Connected Network of Core Bacteria on Microplastics.

Core microbiota is shared microbial taxa within the same habitat, which is important for understanding the stable and consistent components of the complex microbial assembly. However, information on the microplastic core bacteria from the river ecosystems is poor. Here, we investigated the composition and function of microplastic core bacteria from the Three Gorges Reservoir area along the approximate 662 km of the Yangtze River via full-length 16S rRNA gene sequencing, compared with those in water, sediment, and soil. The results showed that the spatial turnover of bacterial communities in four habitats supported deterministic processes dominated by niche differentiation, which shaped their core bacteria. The composition and function of microplastic core bacteria were significantly different from those in the other three habitats. Rhodobacteraceae was the main component of microplastic core bacteria, while the main component of core bacteria in water, sediment, and soil were Burkholderiaceae (21.90%), Burkholderiaceae (5.01%), Nitrosomonadaceae (4.61%), respectively. Furthermore, microplastic core bacteria had stronger geographic limitations along the Yangtze River in the Three Gorges Reservoir area. Stronger geographic limitations shaped the rapid community turnover and a potentially more connected network for the microplastic core bacteria than water, sediment, and soil. More importantly, microplastic core bacteria had strong potential functions of drug resistance and could cause risks to ecosystems and human health. Microplastic core bacteria were mainly influenced by sediment core bacteria, although the bacteria colonizing on microplastics could be from all the contact environments and original sources. These findings provide important insights into the composition, function, and association of microplastic core bacteria with their surrounding environment.

Salinity-triggered homogeneous selection constrains the microbial function and stability in lakes.

Climate change and anthropogenic exploitation have led to the gradual salinization of inland waters worldwide. However, the impacts of this process on the prokaryotic plankton communities and their role in biogeochemical cycles in the inland lake are poorly known. Here, we take a space-for-time substitution approach, using 16S rRNA gene amplicon sequencing and metagenomic sequencing. We analyzed the prokaryotic plankton communities of 11 lakes in northwest China, with average water salinities ranging from 0.002 to 14.370%. The results demonstrated that, among the various environmental parameters, salinity was the most important driver of prokaryotic plankton ß-diversity (Mantel test, r = 0.53, P < 0.001). (1) Under low salinity, prokaryotic planktons were assembled by stochastic processes and employed diverse halotolerant strategies, including the synthesis and uptake of compatible solutes and extrusion of Na+ or Li+ in exchange for H+. Under elevated salinity pressure, strong homogeneous selection meant that only planktonic prokaryotes showing an energetically favorable halotolerant strategy employing an Mnh-type Na+/H+ antiporter remained. (2) The decreasing taxonomic diversity caused by intense environmental filtering in high-salinity lakes impaired functional diversity related to substance metabolism. The prokaryotes enhanced the TCA cycle, carbon fixation, and low-energy-consumption amino acid biosynthesis in high-salinity lakes. (3) Elevated salinity pressure decreased the negative:positive cohesion and the modularity of the molecular ecology networks for the planktonic prokaryotes, indicating a precarious microbial network. Our findings provide new insights into plankton ecology and are helpful for the protecting of the biodiversity and function of inland lakes against the background of salinization. KEY POINTS: • Increased salinity enhances homogeneous selection in the microbial assembly. • Elevated salinity decreases the microbial co-occurrence networks stability. • High salinity damages the microbial function diversity.

Distinct strategies of the habitat generalists and specialists in sediment of Tibetan lakes.

Microbial metacommunities normally comprise generalists and specialists. Uncovering the mechanisms underlying the diversity patterns of these two sub-communities is crucial for aquatic biodiversity maintenance. However, little is known about the ecological assembly processes and co-occurrence patterns of the habitat generalists and specialists across large spatial scales in plateau lake sediments, particularly regarding their environmental adaptations. Here, we investigated assembly processes of the habitat generalists and specialists in sediment of Tibetan lakes and their role in the stability of metacommunity co-occurrence network. Our results showed that the habitat generalists exhibited broader environmental thresholds and closer phylogenetic clustering than specialist counterparts. In contrast, the specialists exhibited stronger phylogenetic signals of ecological preferences compared with the habitat generalists. Stochastic processes dominated the habitat generalist (63.2%) and specialist (81.3%) community assembly. Sediment pH was the major factor mediating the balance between stochastic and deterministic processes in the habitat generalists and specialists. In addition, as revealed by network analysis, the habitat specialists played a greater role in maintaining the stability of metacommunity co-occurrence network. The insights gained from this study can be helpful to understand the mechanisms underlying maintenance of sediment microbial diversity in plateau lakes.

Effective immobilization of heavy metals via reactive barrier by rhizosphere bacteria and their biofilms.

As the portal of plants, rhizosphere microorganisms play an essential role in controlling the species, transformation, and bioavailability of heavy metals, yet the potential passivation mechanism is still unclear. In this study, two heavy metal resistant and growth-promoting rhizosphere bacteria were screened, and their mechanisms in dealing with external stress and immobilizing heavy metal were explored. The results showed that heavy metals inhibited the ability of Pseudomonas sp. H13 and Brevundomonas sp. H16 to promote plant growth, but stimulated the production of extracellular polysaccharides and inorganic labile sulfide, and enhanced biofilm formation, thereby significantly improved the removal efficiency of Cu2+, Zn2+, Cd2+, and Pb2+. Compared with H16, the biofilm of H13 disintegrated rapidly in the later stage, so more metal ions were adsorbed on the planktonic cells. The C-OH and PO groups related to polysaccharides play a crucial role in heavy metal adsorption, and the immobilization mechanism of the planktonic cell is mainly ion exchange and group complex, but for H16, intracellular enrichment cannot be ignored. Functional group complexes played a dominant role in biofilm, and the immobilized heavy metals were more difficult to release into the environment. This study highlighted the potential application prospects of biofilm bacteria in heavy metal remediation and explained the reactive barrier of rhizosphere bacteria to heavy metals.

Associations between PM2.5 exposure and Alzheimer's Disease prevalence Among elderly in eastern China.

BACKGROUND: Studies showed that PM2.5 might be associated with various neurogenic diseases such as Alzheimer's Disease (AD). However, this topic had been little studied in Zhejiang province of China.  METHODS: In 2018, we established a cohort of AD high-risk population with 1,742 elderly aged 60 and above. In 2020, the cohort was followed up, a total of 1,545 people participated the 2 surveys. Data collection included questionnaires and basic physical examinations. The average residential exposure to PM2.5 for each participant, that in a 5-years period prior to the first survey, was estimated using a satellite-based spatial statistical model. We determined the association between PM2.5 and AD prevalence by cox proportional hazards regression model.  RESULTS: This study showed that an increase in the PM2.5 level was an important associated risk factor that contributed to AD. The average PM2.5 exposure levels among the study population ranged from 32.69 µg/m3 to 39.67 µg/m3 from 2013 to 2017, which were much higher than 5 µg/m3 that specified in the WHO air quality guidelines. There was an association between PM2.5 exposure and AD, and the correlations between PM2.5 and Mini-Mental State Examination, Montreal cognitive assessment scale scores were statistically significant. An increase in the PM2.5 level by 10 µg/m3 elevated the risk of AD among residents by 2%-5% (HR model 2-model 4 = 1.02 to 1.05, CI model 2-model 4 = 1.01-1.10). The subgroups of male, with old age, with low education levels, used to work as farmers or blue-collar workers before retirement, overweight and obese were associated with a higher effect of PM2.5. CONCLUSIONS: Reducing PM2.5 exposure might be a good way to prevent AD.

High Salinity Inhibits Soil Bacterial Community Mediating Nitrogen Cycling.

Salinization is considered a major threat to soil fertility and agricultural productivity throughout the world. Soil microbes play a crucial role in maintaining ecosystem stability and function (e.g., nitrogen cycling). However, the response of bacterial community composition and community-level function to soil salinity remains uncertain. Here, we used multiple statistical analyses to assess the effect of high salinity on bacterial community composition and potential metabolism function in the agricultural ecosystem. Results showed that high salinity significantly altered both bacterial alpha (Shannon-Wiener index and phylogenetic diversity) and beta diversity. Salinity, total nitrogen (TN), and soil organic matter (SOM) were the vital environmental factors shaping bacterial community composition. The relative abundance of Actinobacteria, Chloroflexi, Acidobacteria, and Planctomycetes decreased with salinity, whereas Proteobacteria and Bacteroidetes increased with salinity. The modularity and the ratio of negative to positive links remarkedly decreased, indicating that high salinity destabilized bacterial networks. Variable selection, which belongs to deterministic processes, mediated bacterial community assembly within the saline soils. Function prediction results showed that the key nitrogen metabolism (e.g., ammonification, nitrogen fixation, nitrification, and denitrification processes) was inhibited in high salinity habitats. MiSeq sequencing of 16S rRNA genes revealed that the abundance and composition of the nitrifying community were influenced by high salinity. The consistency of function prediction and experimental verification demonstrated that high salinity inhibited soil bacterial community mediating nitrogen cycling. Our study provides strong evidence for a salinity effect on the bacterial community composition and key metabolism function, which could help us understand how soil microbes respond to ongoing environment perturbation. IMPORTANCE Revealing the response of the soil bacterial community to external environmental disturbances is an important but poorly understood topic in microbial ecology. In this study, we evaluated the effect of high salinity on the bacterial community composition and key biogeochemical processes in salinized agricultural soils (0.22 to 19.98 dS m-1). Our results showed that high salinity significantly decreased bacterial diversity, altered bacterial community composition, and destabilized the bacterial network. Moreover, variable selection (61% to 66%) mediated bacterial community assembly within the saline soils. Functional prediction combined with microbiological verification proved that high salinity inhibited soil bacterial community mediating nitrogen turnover. Understanding the impact of salinity on soil bacterial community is of great significance for managing saline soils and maintaining a healthy ecosystem.

Environmental adaptation is stronger for abundant rather than rare microorganisms in wetland soils from the Qinghai-Tibet Plateau.

Disentangling the biogeographic patterns of rare and abundant microbes is essential in order to understand the generation and maintenance of microbial diversity with respect to the functions they provide. However, little is known about ecological assembly processes and environmental adaptation of rare and abundant microbes across large spatial-scale wetlands. Using Illumina sequencing and multiple statistical analyses, we characterized the taxonomic and phylogenetic diversity of rare and abundant bacteria and fungi in Qinghai-Tibet Plateau wetland soils. Abundant microbial taxa exhibited broader environmental thresholds and stronger phylogenetic signals for ecological traits than rare ones. By contrast, rare taxa showed higher sensitivity to environmental changes and closer phylogenetic clustering than abundant ones. The null model analysis revealed that dispersal limitation belonging to stochastic process dominated community assemblies of abundant bacteria, and rare and abundant fungi, while variable selection belonging to deterministic process governed community assembly of rare bacteria. Neutral model analysis and variation partitioning analysis further confirmed that abundant microbes were less environmentally constrained. Soil ammonia nitrogen was the crucial factor in mediating the balance between stochasticity and determinism of both rare and abundant microbes. Abundant microbes may have better environmental adaptation potential and are less dispersed by environmental changes than rare ones. Our findings extend knowledge of the adaptation of rare and abundant microbes to ongoing environmental change and could facilitate prediction of biodiversity loss caused probably by climate change and human activity in the Qinghai-Tibet Plateau wetlands.

Imaging through dynamical scattering media by two-photon absorption detectors.

Imaging through a dynamical opaque scattering medium is an almost impossible task, where strong multiple light scattering from moving scatters dynamically prevents imaging formations even with state-of-art techniques like correlation imaging or adaptive optics. Meanwhile, a small number of ballistic photons can still penetrate through but require demanding detection in terms of a ultrashort time gate and high sensitivity. However, visible light is strongly scattered for most of scattering media. Here we experimentally demonstrate a non-invasive coherent imaging scheme based on two-photon absorption capable of imaging through dynamical scattering media with a length equivalent to 28 times mean free paths for single photon transport, where two-photon absorption in a conventional semiconductor photodetector when phase matching is not required works over a wide bandwidth so it can support a fast time gate down to femtosecond level, short enough to distinguish ballistic photons from scattering background, and allows accessing longer wavelengths for deeper penetration. This technique combined with successful optical coherence tomography may pave a new way for imaging through fog, storm, and rain as well as biomedical imaging applications.

Label-free plasmonic assisted optical trapping of single DNA molecules.

DNA molecules are hard to catch using traditional optical trapping due to the nanometer width of their chains. Here we experimentally demonstrate a label-free optical trapping of a single micrometer λ-DNA in solution by the aid of plasmonic gold nanoparticles (GNPs), where a double-laser trap induces strong optical interparticle forces for the tweezer. We examine such sub-resolved interparticle forces by tracking the GNP dynamics in solution. Moreover, surface-enhanced Raman scattering signals of trapped λ-DNA have also been measured simultaneously in the same setup. In comparison with prior works, ours benefit from the excitation in a dynamic configuration without fabrication. This technique opens a new avenue for all-optical manipulation of biomolecules, as well as ultra-sensitive bio-medical sensing applications.

Vibrational modes in an optically levitated droplet.

Levitation by optical tweezers provides a unique non-invasive tool for investigating a microscale object without external perturbations. Here we experimentally levitate a micrometer-sized water droplet in the air using an optical tweezer. Meanwhile, vibrational modes of a levitated water droplet are excited by modulating the trapping laser. From their backscattered light, vibrational modes with mode numbers are observed in the spectra. Additionally, their corresponding free spectral ranges are analyzed and compared with theory and numerical simulations. This Letter, establishing a non-invasive and all-optical detection technique of optomechanical properties of levitated droplets, paves the way for their practical applications in aerosol and biomedical science.

Generation of Optical Frequency Comb via Giant Optomechanical Oscillation.

Optical frequency combs (OFCs) are essential in precision metrology, spectroscopy, distance measurement, and optical communications. Significant advances have been made recently in achieving micro-OFC devices based on parametric frequency conversion or electro-optic phase modulation. Here, we demonstrate a new kind of microcomb using a cavity optomechanical system with giant oscillation amplitude. We observe both optical and microwave frequency combs in a microtoroid resonator, which feature a flat OFC with 938 comb lines and a repetition rate as low as 50.22 MHz, as well as a flat microwave frequency comb with 867 comb lines. To generate such giant oscillation amplitude, we excite an overcoupled optical mode with a large blue detuning that is assisted with the thermo-optic nonlinearity. A new type of nonlinear oscillation, induced by competition between the optomechanical oscillation and thermo-optic nonlinearity, is also observed.

Counting-loss correction method based on dual-exponential impulse shaping.

Under the condition of high counting rate, the phenomenon of nuclear pulse signal pile-up using a single exponential impulse shaping method is still very serious, and leads to a severe loss in counting rate. A real nuclear pulse signal can be expressed as a dual-exponential decay function with a certain rising edge. This paper proposes a new dual-exponential impulse shaping method and shows its deployment in hardware to test its performance. The signal of a high-performance silicon drift detector under high counting rate in an X-ray fluorescence spectrometer is obtained. The result of the experiment shows that the new method can effectively shorten the dead-time caused by nuclear signal pile-up and correct the counting rate.

Controllable coupling between an ultra-high-Q microtoroid cavity and a graphene monolayer for optical filtering and switching applications.

Whispering-gallery-mode optical microresonators have found impactful applications in various areas due to their remarkable properties such as ultra-high quality factor (Q-factor), small mode volume, and strong evanescent field. Among these applications, controllable tuning of the optical Q-factor is vital for on-chip optical modulation and various opto-electronic devices. Here, we report an experimental demonstration with a hybrid structure formed by an ultra-high-Q microtoroid cavity and a graphene monolayer. Thanks to the strong interaction of the evanescent wave with the graphene, the structure allows the Q-factor to be controllably varied in the range of 3.9 × 105 ∼ 6.2 × 107 by engineering optical absorption via changing the gap distance in between. At the same time, a resonant wavelength shift of 32 pm was also observed. Besides, the scheme enables us to approach the critical coupling with a coupling depth of 99.6%. As potential applications in integrated opto-electronic devices, we further use the system to realize a tunable optical filter with tunable bandwidth from 116.5 MHz to 2.2 GHz as well as an optical switch with a maximal extinction ratio of 31 dB and response time of 21 ms.

Resolution enhanced photothermal imaging by high-order correlation.

Laser scanning photothermal imaging offers a powerful non-destructive testing tool to visualize subsurface structures of opaque materials, but it suffers the resolution limit imposed by thermal diffusion. To overcome this physical obstacle, a tightly focused excitation beam with a high repetition rate is usually used to improve the spatial resolution. Here, we demonstrate that the resolution of photothermal imaging could be enhanced using the high-order correlation imaging method inspired by correlated optical imaging. By carefully designing the laser scanning and modulation behavior, we can individually control the statistical properties of isolated hotspots induced by lasers. Imaging reconstructions of subsurface structures are performed afterward by reading out time-fluctuated thermal images. Moreover, the resolution can be further enhanced by using the high-order correlation, which enables a new way for highly resolved thermal imaging and metrology applications.