Beam combining of a broadly and continuously tunable quantum cascade laser.

We report a cost-efficient method to demonstrate the beam combining of five laser elements in an array of tunable slot waveguide quantum cascade lasers in the mid-infrared region at around 10 µm. An aspherical lens with five fine-tuned mini mirrors was employed to collimate the individual beams from the laser array. To verify the feasibility of this beam combining approach, the combined beams were coupled into a hollow-core fiber gas cell with a low numerical aperture (N.A.) of 0.03 and a coupling efficiency >= 0.82, for gas sensing of binary compound gases of ammonia and ethylene simultaneously.

Reliability of monitoring acid-base and electrolyte parameters through circuit lines during regional citrate anticoagulation-continuous renal replacement therapy.

BACKGROUND: The current practice involves blood sampling from the circuit line to measure acid-base and electrolyte parameters during continuous renal replacement therapy (CRRT). However, there is limited evidence supporting its reliability due to the effects of anticoagulant mechanism and access recirculation associated with regional citrate anticoagulation (RCA). AIM: To evaluate the reliability of monitoring acid-base and electrolyte parameters through circuit lines in regular and reversed connections during RCA-CRRT. STUDY DESIGN: In this prospective cohort study, we included critically ill patients receiving RCA-CRRT via a double-lumen catheter. During the second hour after CRRT initiation, we collected blood samples to monitor acid-base and electrolyte parameters and their levels were compared between samples from the circuit lines (at 0, 3, and 5 minutes) and those from the central venous catheter (CVC) line (at 0 minute). During this time, CRRT switched to the replacement state as controls. RESULTS: We observed 128 CRRT circuits in 60 adult patients receiving RCA-CRRT. Ninety-eight (76.6%) circuits had regular connections, while 30 (23.4%) had reversed connections. Among regular connections, no differences were observed in any acid-base or electrolyte parameters between samples from the CVC line and those from the circuit line at all time points (P > .05). Among reversed connections, ionized calcium levels were dramatically decreased at all three time points in samples from the circuit line compared with those from the CVC line (0.65 ± 0.12, 0.72 ± 0.11, and 0.78 ± 0.99 vs 0.98 ± 0.07 mmol/L, P < .001), with comparable levels of other acid-base or electrolyte parameters between the sampling patterns (P > .05). CONCLUSIONS: Acid-base and electrolyte parameters could be reliably monitored through the circuit line during RCA-CRRT in regular connections. However, in reversed connections, pre-filter ionized calcium concentrations determined through the circuit line were lower than those determined through the CVC line. RELEVANCE TO CLINICAL PRACTICE: We suggest sampling from arterial or CVC lines rather than from the circuit line in a reversed connection during RCA-CRRT.

Enhanced Piezoelectric Effect Derived from Grain Boundary in MoS2 Monolayers.

Recent discovery of piezoelectricity that existed in two-dimensional (2D) layered materials represents a key milestone for flexible electronics and miniaturized and wearable devices. However, so far the reported piezoelectricity in these 2D layered materials is too weak to be used for any practical applications. In this work, we discovered that grain boundaries (GBs) in monolayer MoS2 can significantly enhance its piezoelectric property. The output power of piezoelectric devices made of the butterfly-shaped monolayer MoS2 was improved about 50% by the GB-induced piezoelectric effect. The enhanced piezoelectricity is attributed to the additional piezoelectric effect induced by the existence of deformable GBs which can promote polarization and generates spontaneous polarization with different piezoelectric coefficients along various directions. We further made a flexible piezoelectric device based on the 2D MoS2 with the GBs and demonstrated its potential application in self-powered precision sensors for in situ detecting pressure changes in human blood for health monitoring.

Two-Dimensional van der Waals Materials with Aligned In-Plane Polarization and Large Piezoelectric Effect for Self-Powered Piezoelectric Sensors.

Piezoelectric two-dimensional (2D) van der Waals (vdWs) materials are highly desirable for applications in miniaturized and flexible/wearable devices. However, the reverse-polarization between adjacent layers in current 2D layered materials results in decreasing their in-plane piezoelectric coefficients with layer number, which limits their practical applications. Here, we report a class of 2D layered materials with an identical orientation of in-plane polarization. Their piezoelectric coefficients (e22) increase with layer number, thereby allowing for the fabrication of flexible piezotronic devices with large piezoelectric responsivity and excellent mechanical durability. The piezoelectric outputs can reach up to 0.363 V for a 7-layer α-In2Se3 device, with a current responsivity of 598.1 pA for 1% strain, which is 1 order of magnitude higher than the values of the reported 2D piezoelectrics. The self-powered piezoelectric sensors made of these newly developed 2D layered materials have been successfully used for real-time health monitoring, proving their suitability for the fabrication of flexible piezotronic devices due to their large piezoelectric responses and excellent mechanical durability.

Shape evolution of two dimensional hexagonal boron nitride single domains on Cu/Ni alloy and its applications in ultraviolet detection.

Two dimensional (2D) hexagonal boron nitride (h-BN) has attracted extensive attention due to its high thermal and chemical stability, excellent dielectric characteristic, and unique optical properties. However, the chemical vapor deposition synthesis of 2D h-BN is not fully explored, such as morphology regulation and size control. Here we demonstrate the growth of 2D h-BN single domains on Cu/Ni alloy via atmospheric chemical vapor deposition (APCVD). We discover that the shape of the as-grown h-BN single domains can be controlled from triangles, hexagons, to circles by adjusting the Ni content of the Cu/Ni substrates. Moreover, we find out that increasing the nickel content can suppress the nucleation density while the average domain size is accordingly improved. The grown single-crystalline h-BN demonstrates ultralow dark current about 0.9 pA and outstanding ultraviolet response with the responsivity up to 5.45 mAW-1. The response time are 376 and 198 ms. Our work sheds light on the controllable synthesis of 2D h-BN and promotes its applications in high ultraviolet detection.

High-performance and flexible photodetectors based on chemical vapor deposition grown two-dimensional In2Se3 nanosheets.

Two-dimensional (2D) In2Se3 with unique optical and electrical properties has great potential in next generation optoelectronics and multilevel phase-change memories. Here, for the first time, we report high-performance rigid and flexible photodetectors based on chemical vapor deposition (CVD) grown 2D In2Se3. Both rigid and flexible 2D In2Se3 photodetectors show a broadband response range from ultraviolet (254 nm) to visible light (700 nm). High photoresponsivities of 578 and 363 A · W-1 are achieved using rigid and flexible 2D In2Se3 photodetectors, respectively, under 700 nm light illumination, which are higher than those of photodetectors based on mechanically exfoliated 2D In2Se3 and physical vapor deposition grown 2D In2Se3. Furthermore, flexible 2D In2Se3 photodetectors show good mechanical durability and photoresponse stability under repeated bending tests. A high and stable photoresponse provides an opportunity for CVD-grown 2D In2Se3 applications in flexible optoelectronic and photovoltaic devices.

On-chip photodetection of angular momentums of vortex structured light.

Structured vortex light with orbital angular momentum (OAM) shows great promise for high-bandwidth optical communications, quantum information and computing, optical tweezers, microscopy, astronomy, among others. Generating, controlling, and detecting of vortex light by all-electrical means is at the heart of next generation nanophotonic platforms. However, on-chip electrical photodetection of structured vortex light remains challenging. Here, we propose an on-chip photodetector based on 2D broadband thermoelectric material (PdSe2) with a well-designed spin-Hall couplers to directly characterize angular momentum modes of vortex structured light. Photothermoelectric responses in the PdSe2 nanoflake, excited by the focusing surface plasmons, show a magnitude proportional to the total angular momentum modes of the infrared vortex beams, thereby achieving direct detection of spin and orbital angular momentum, as well as the chirality and ellipticity of scalar vortex lights. Our works provide a promising strategy for developing on-chip angular momentum optoelectronic devices, which play a key role in the next-generation high-capacity optical communications, quantum information and computing, imaging, and other photonic systems.

Multidimensional detection enabled by twisted black arsenic-phosphorus homojunctions.

A light field carrying multidimensional optical information, including but not limited to polarization, intensity and wavelength, is essential for numerous applications such as environmental monitoring, thermal imaging, medical diagnosis and free-space communications. Simultaneous acquisition of this multidimensional information could provide comprehensive insights for understanding complex environments but remains a challenge. Here we demonstrate a multidimensional optical information detection device based on zero-bias double twisted black arsenic-phosphorus homojunctions, where the photoresponse is dominated by the photothermoelectric effect. By using a bipolar and phase-offset polarization photoresponse, the device operated in the mid-infrared range can simultaneously detect both the polarization angle and incident intensity information through direct measurement of the photocurrents in the double twisted black arsenic-phosphorus homojunctions. The device's responsivity makes it possible to retrieve wavelength information, typically perceived as difficult to obtain. Moreover, the device exhibits an electrically tunable polarization photoresponse, enabling precise distinction of polarization angles under low-intensity light exposure. These demonstrations offer a promising approach for simultaneous detection of multidimensional optical information, indicating potential for diverse photonic applications.

Extraordinary Enhancement of Nonlinear Optical Interaction in NbOBr2 Microcavities.

2D materials are burgeoning as promising candidates for investigating nonlinear optical effects due to high nonlinear susceptibilities, broadband optical response, and tunable nonlinearity. However, most 2D materials suffer from poor nonlinear conversion efficiencies, resulting from reduced light-matter interactions and lack of phase matching at atomic thicknesses. Herein, a new 2D nonlinear material, niobium oxide dibromide (NbOBr2) is reported, featuring strong and anisotropic optical nonlinearities with scalable nonlinear intensity. Furthermore, Fabry-Pérot (F-P) microcavities are constructed by coupling NbOBr2 with air holes in silicon. Remarkable enhancement factors of ≈630 times in second harmonic generation (SHG) and 210 times in third harmonic generation (THG) are achieved on cavity at the resonance wavelength of 1500 nm. Notably, the cavity enhancement effect exhibits strong anisotropic feature tunable with pump wavelength, owing to the robust optical birefringence of NbOBr2. The ratio of the enhancement factor along the b- and c-axis of NbOBr2 reaches 2.43 and 5.27 for SHG and THG at 1500 nm pump, respectively, which leads to an extraordinarily high SHG anisotropic ratio of 17.82 and a 10° rotation of THG polarization. The research presents a feasible and practical strategy for developing high-efficiency and low-power-pumped on-chip nonlinear optical devices with tunable anisotropy.

Light-Induced Electric Field Enhanced Self-Powered Photodetector Based on Van der Waals Heterojunctions.

Self-powered photodetectors have attracted widespread attention due to their low power consumption which can be driven by the built-in electric field instead of external power, but it is very difficult to achieve high responsivity and fast response speed concurrently. Here, a self-powered photodetector with light-induced electric field enhancement based on a 2D InSe/WSe2 /SnS2 van der Waals heterojunction is designed. The light-induced electric field derived from the photo-generated electrons of SnS2 accumulated at the SnS2 /WSe2 interface produces an additional negative gate voltage applied to the WSe2 layer, which enhances the built-in electric field in the InSe/WSe2 /SnS2 heterojunction. Accordingly, the photocurrent and photoresponse speed of the heterostructure device are largely improved. The self-powered photodetector based on the InSe/WSe2 /SnS2 heterostructure exhibits a high responsivity of 550 mA W-1 , which is a 50 times increase compared to the InSe/WSe2 photodetector, and the response speed (110/120 µs) is one order of magnitude faster than that of the InSe/WSe2 photodetector. The high responsivity and fast speed are caused by the stronger built-in electric field modulated by a light-induced electric field, which can separate carriers effectively and reduce drift times. This device architecture can provide a new avenue to fabricate high-responsivity, fast self-power photodetectors by utilizing the van der Waals heterojunction.

Long-wave infrared photothermoelectric detectors with ultrahigh polarization sensitivity.

Filter-free miniaturized polarization-sensitive photodetectors have important applications in the next-generation on-chip polarimeters. However, their polarization sensitivity is thus far limited by the intrinsic low diattenuation and inefficient photon-to-electron conversion. Here, we implement experimentally a miniaturized detector based on one-dimensional tellurium nanoribbon, which can significantly improve the photothermoelectric responses by translating the polarization-sensitive absorption into a large temperature gradient together with the finite-size effect of a perfect plasmonic absorber. Our devices exhibit a zero-bias responsivity of 410 V/W and an ultrahigh polarization ratio (2.5 × 104), as well as a peak polarization angle sensitivity of 7.10 V/W•degree, which is one order of magnitude higher than those reported in the literature. Full linear polarimetry detection is also achieved with the proposed device in a simple geometrical configuration. Polarization-coded communication and optical strain measurement are demonstrated showing the great potential of the proposed devices. Our work presents a feasible solution for miniaturized room-temperature infrared photodetectors with ultrahigh polarization sensitivity.

Mid-Infrared Bipolar and Unipolar Linear Polarization Detections in Nb2 GeTe4 /MoS2 Heterostructures.

Detecting and distinguishing light polarization states, one of the most basic elements of optical fields, have significant importance in both scientific studies and industry applications. Artificially fabricated structures, e.g., metasurfaces with anisotropic absorptions, have shown the capabilities of detecting polarization light and controlling. However, their operations mainly rely on resonant absorptions based on structural designs that are usually narrow bands. Here, a mid-infrared (MIR) broadband polarization photodetector with high PRs and wavelength-dependent polarities using a 2D anisotropic/isotropic Nb2 GeTe4 /MoS2 van der Waals (vdWs) heterostructure is demonstrated. It is shown that the photodetector exhibits high PRs of 48 and 34 at 4.6  and 11.0 µm wavelengths, respectively, and even a negative PR of -3.38 for 3.7 µm under the zero bias condition at room temperature. Such interesting results can be attributed to the superimposed effects of a photovoltaic (PV) mechanism in the Nb2 GeTe4 /MoS2 hetero-junction region and a bolometric mechanism in the MoS2 layer. Furthermore, the photodetector demonstrates its effectiveness in bipolar and unipolar polarization encoding communications and polarization imaging enabled by its unique and high PRs.

Inventory of cadmium-transporter genes in the root of mangrove plant Avicennia marina under cadmium stress.

Mangrove Avicennia marina has the importantly potential for cadmium (Cd) pollution remediation in coastal wetlands. Unfortunately, the molecular mechanisms and transporter members for Cd uptake by the roots of A. marina are not well documented. In this study, photosynthetic and phenotypic analysis indicated that A. marina is particularly tolerant to Cd. The content and flux analysis indicated that Cd is mainly retained in the roots, with greater Cd influx in fine roots than that in coarse roots, and higher Cd influx in the root meristem zone as well. Using transcriptomic analysis, a total of 5238 differentially expressed genes were identified between the Cd treatment and control group. Moreover, we found that 54 genes were responsible for inorganic ion transport. Among these genes, AmHMA2, AmIRT1, and AmPCR2 were localized in the plasma membrane and AmZIP1 was localized in both plasma membrane and cytoplasm. All above gene encoding transporters showed significant Cd transport activities using function assay in yeast cells. In addition, the overexpression of AmZIP1 or AmPCR2 in Arabidopsis improved the Cd tolerance of transgenic plants. This is particularly significant as it provides insight into the molecular mechanism for Cd uptake by the roots of mangrove plants and a theoretical basis for coastal wetland phytoremediation.

Electrically-pumped compact topological bulk lasers driven by band-inverted bound states in the continuum.

One of the most exciting breakthroughs in physics is the concept of topology that was recently introduced to photonics, achieving robust functionalities, as manifested in the recently demonstrated topological lasers. However, so far almost all attention was focused on lasing from topological edge states. Bulk bands that reflect the topological bulk-edge correspondence have been largely missed. Here, we demonstrate an electrically pumped topological bulk quantum cascade laser (QCL) operating in the terahertz (THz) frequency range. In addition to the band-inversion induced in-plane reflection due to topological nontrivial cavity surrounded by a trivial domain, we further illustrate the band edges of such topological bulk lasers are recognized as the bound states in the continuum (BICs) due to their nonradiative characteristics and robust topological polarization charges in the momentum space. Therefore, the lasing modes show both in-plane and out-of-plane tight confinements in a compact laser cavity (lateral size ~3λlaser). Experimentally, we realize a miniaturized THz QCL that shows single-mode lasing with a side-mode suppression ratio (SMSR) around 20 dB. We also observe a cylindrical vector beam for the far-field emission, which is evidence for topological bulk BIC lasers. Our demonstration on miniaturization of single-mode beam-engineered THz lasers is promising for many applications including imaging, sensing, and communications.

A two-dimensional mid-infrared optoelectronic retina enabling simultaneous perception and encoding.

Infrared machine vision system for object perception and recognition is becoming increasingly important in the Internet of Things era. However, the current system suffers from bulkiness and inefficiency as compared to the human retina with the intelligent and compact neural architecture. Here, we present a retina-inspired mid-infrared (MIR) optoelectronic device based on a two-dimensional (2D) heterostructure for simultaneous data perception and encoding. A single device can perceive the illumination intensity of a MIR stimulus signal, while encoding the intensity into a spike train based on a rate encoding algorithm for subsequent neuromorphic computing with the assistance of an all-optical excitation mechanism, a stochastic near-infrared (NIR) sampling terminal. The device features wide dynamic working range, high encoding precision, and flexible adaption ability to the MIR intensity. Moreover, an inference accuracy more than 96% to MIR MNIST data set encoded by the device is achieved using a trained spiking neural network (SNN).

High-Performance, Polarization-Sensitive, Long-Wave Infrared Photodetection via Photothermoelectric Effect with Asymmetric van der Waals Contacts.

Long-wavelength infrared (LWIR) photodetection is important for heat-seeking technologies, such as thermal imaging, all-weather surveillance, and missile guidance. Among various detection techniques, photothermoelectric (PTE) detectors are promising in that they can realize ultra-broadband photodetection at room temperature without an external power supply. However, their performance in terms of speed, responsivity, and noise level in the LWIR regime still needs further improvement. Here, we demonstrated a high-performance PTE photodetector based on low-symmetry palladium selenide (PdSe2) with asymmetric van der Waals contacts. The temperature gradient induced by asymmetric van der Waals contacts even under global illumination drives carrier diffusion to produce a photovoltage via the PTE effect. A responsivity of over 13 V/W, a response time of ∼50 µs, and a noise equivalent power of less than 7 nW/Hz1/2 are obtained in the 4.6-10.5 µm regime at room temperature. Furthermore, due to the anisotropic absorption of PdSe2, the detector exhibits a linear polarization angle sensitive response with an anisotropy ratio of 2.06 at 4.6 µm and 1.21 at 10.5 µm, respectively. Our proposed device architecture provides an alternative strategy to design high-performance photodetectors in the LWIR regime by utilizing van der Waals layered materials.

On-chip mid-infrared photothermoelectric detectors for full-Stokes detection.

On-chip polarimeters are highly desirable for the next-generation ultra-compact optical and optoelectronic systems. Polarization-sensitive photodetectors relying on anisotropic absorption of natural/artificial materials have emerged as a promising candidate for on-chip polarimeters owing to their filterless configurations. However, these photodetectors can only be applied for detection of either linearly or circularly polarized light, not applicable for full-Stokes detection. Here, we propose and demonstrate three-ports polarimeters comprising on-chip chiral plasmonic metamaterial-mediated mid-infrared photodetectors for full-Stokes detection. By manipulating the spatial distribution of chiral metamaterials, we could convert polarization-resolved absorptions to corresponding polarization-resolved photovoltages of three ports through the photothermoelectric effect. We utilize the developed polarimeter in an imaging demonstration showing reliable ability for polarization reconstruction. Our work provides an alternative strategy for developing polarization-resolved photodetectors with a bandgap-independent operation range in the mid-infrared.

Strong In-Plane Optical and Electrical Anisotropies of Multilayered γ-InSe for High-Responsivity Polarization-Sensitive Photodetectors.

Recently, identifying promising new two-dimensional (2D) materials with low-symmetry structures has aroused great interest for developing monolithic polarization-sensitive photodetectors with small volume. Here, after comprehensive research of the in-plane anisotropic structure and electronic and optoelectronic properties of layered γ-InSe, a superior responsivity polarization-sensitive photodetector based on multilayer γ-InSe is constructed by a facile method. Notably, the conductance and carrier mobility of the device along the armchair direction are 11.8 and 2.35 times larger than those along the zigzag direction, respectively. Benefitting from the high efficiency of light absorption and excellent carrier mobility (221 cm2 V-1 s-1) of our multilayered γ-InSe along the armchair direction, the device exhibits a superior responsivity of 127 A/W and an external quantum efficiency (EQE) of 104%. Especially, the highest responsivity along the armchair direction of our γ-InSe polarization-sensitive photodetectors can reach as high as 78.5 A/W under polarized light. This value is much higher than those of other devices even under unpolarized light. This work not only provides an insight into the in-plane anisotropic properties of 2D layered γ-InSe but also proposes a stable and environmentally friendly candidate for anisotropic optoelectronic applications.

Carrier Recirculation Induced High-Gain Photodetector Based on van der Waals Heterojunction.

Two-dimensional (2D) materials have attracted great attention in the field of photodetection due to their excellent electronic and optoelectronic properties. However, the weak optical absorption caused by atomically thin layers and the short lifetime of photocarriers limit their optoelectronic performance, especially for weak light detection. In this work, we design a high-gain photodetector induced by carrier recirculation based on a vertical InSe/GaSe heterojunction. In this architecture, the photogenerated holes are trapped in GaSe due to the built-in electric field, suppressing the recombination rate of photocarriers, so the electrons can recirculate for multiple times in the InSe channel following the generation of a single electron-hole pair, resulting a high photoconductive gain (107). The responsivity and detectivity of the InSe/GaSe heterojunction can reach 1037 A/W and 8.6 × 1013 Jones, which are 1 order of magnitude higher than those of individual InSe. More importantly, the InSe/GaSe heterojunction can respond to weaker light (1 µW/cm2) compared to individual InSe (10 µW/cm2). Utilizing GaSe as the channel and InSe as the electrons trapped layer, the same experimental phenomenon is achieved. This work can provide an approach for designing a highly sensitive device utilizing a 2D van der Waals heterojunction, and it also possesses wide applicability for other materials.

Cadmium promotes the absorption of ammonium in hyperaccumulator Solanum nigrum L. mediated by ammonium transporters and aquaporins.

Cadmium (Cd) is a toxic heavy metal affecting the normal growth of plants. Nitrate (NO3-) and ammonium (NH4+) are the primary forms of inorganic nitrogen (N) absorbed by plants. However, the mechanism of N absorption and regulation under Cd stress remains unclear. This study found that: (1) Cd treatment affected the biomass, root length, and Cd2+ flux in Solanum nigrum seedling roots. Specifically, 50 µM Cd significantly inhibited NO3- influx while increased NH4+ influx compared with 0 and 5 µM Cd treatments measured by non-invasive micro-test technology. (2) qRT-PCR analysis showed that 50 µM Cd inhibited the expressions of nitrate transporter genes, SnNRT2;4 and SnNRT2;4-like, increased the expressions of ammonium transporter genes, SnAMT1;2 and SnAMT1;3, in the roots. (3) Under NH4+ supply, 50 µM Cd significantly induced the expressions of the aquaporin genes, SnPIP1;5, SnPIP2;7, and SnTIP2;1. Our results showed that 50 µM Cd stress promoted NH4+ absorption by up-regulating the gene expressions of NH4+ transporter and aquaporins, suggesting that high Cd stress can affect the preference of N nutrition in S. nigrum.