High-power electrically pumped terahertz topological laser based on a surface metallic Dirac-vortex cavity.

Topological lasers (TLs) have attracted widespread attention due to their mode robustness against perturbations or defects. Among them, electrically pumped TLs have gained extensive research interest due to their advantages of compact size and easy integration. Nevertheless, limited studies on electrically pumped TLs have been reported in the terahertz (THz) and telecom wavelength ranges with relatively low output powers, causing a wide gap between practical applications. Here, we introduce a surface metallic Dirac-vortex cavity (SMDC) design to solve the difficulty of increasing power for electrically pumped TLs in the THz spectral range. Due to the strong coupling between the SMDC and the active region, robust 2D topological defect lasing modes are obtained. More importantly, enough gain and large radiative efficiency provided by the SMDC bring in the increase of the output power to a maximum peak power of 150 mW which demonstrates the practical application potential of electrically pumped TLs.

Targeted and Long-Term Fluorescence Imaging of Plant Cytomembranes Using Main-Chain Charged Polyelectrolytes with Aggregation-Induced Emission.

Fluorescent polyelectrolytes have attracted tremendous attention due to their unique properties and wide applications. However, current research objects of fluorescent polyelectrolytes mainly focus on side-chain charged polyelectrolytes, and the applications of polyelectrolytes in plant cytomembrane imaging with long time and high specificity still remain challenging. Herein, long-time and targeted fluorescence imaging of plant cytomembranes was achieved for the first time using main-chain charged polyelectrolytes (MCCPs) with aggregation-induced emission (AIE). A series of MCCPs were designed and synthesized, among which the red-emissive and AIE-active MCCP with a triphenylamine linker and a cyano group around the cationic ring-fused heterocyclic core showed the best fluorescence imaging performance of plant cells. Unlike other MCCPs and its neutral form of polymer, this cyano-substituted conjugated polyelectrolyte can specifically target the cytomembrane of plant cells within a short staining time with many advantages, including wash-free staining, high photostability and imaging integrity, excellent durability (at least 12 h), and low biotoxicity. In addition to onion epidermal cells, this AIE fluorescence probe also shows good imaging capabilities for other kinds of plant cells such as Glycine max and Vigna radiata. Such an AIE-active MCCP-based imaging system provides an effective design strategy to develop fluorescence probes with high specificity and long-term imaging ability toward plant plasma membranes.

Above 20†GHz high frequency operation of mid-infrared doughnut-shaped microcavity quantum cascade lasers.

Microresonator-based high-speed single-mode quantum cascade lasers are ideal candidates for on-chip optical data interconnection and high sensitivity gas sensing in the mid-infrared spectral range. In this paper, we propose a high frequency operation of single-mode doughnut-shaped microcavity quantum cascade laser at ∼4.6 µm. By leveraging compact micro-ring resonators and integrating with grounded coplanar waveguide transmission lines, we have greatly reduced the parasitics originating from both the device and wire bonding. In addition, a selective heat dissipation scheme was introduced to improve the thermal characteristics of the device by semi-insulating InP infill regrowth. The highest continuous wave operating temperature of the device reaches 288 K. A maximum -3 dB bandwidth of 11 GHz and a cut-off frequency exceeding 20 GHz in a microwave rectification technique are obtained. Benefiting from the notch at the short axis of the microcavity resonator, a highly customized far-field profile with an in-plane beam divergence angle of 2.4° is achieved.

Fine-Grained Lithofacies Types and Sedimentary Model of the Upper Permian Longtan Formation Coal Measures in the Western Guizhou Region, South China.

The upper Permian Longtan Formation is widely distributed in southwestern China and is well known for multilayer coal and high organic shale, with significant shale gas potential that has yet to be fully explored and developed. The Longtan coal-bearing strata are composed of complex lithological assemblages of fine-grained sedimentary rocks such as sandstone, coal, shale, and limestone, which exhibit significant differences from marine shale. To better understand the organic-rich lithofacies, their distribution, and their controlling factors, this study carried out a detailed survey of the outcrop and drill cores in the western Guizhou region and examined the fine-grained lithofacies, their assemblages, and their geochemical characteristics. The results showed that (1) the total organic carbon of the Longtan Formation shale in western Guizhou ranged from 1.44 to 14.79%, with an average of 6.41%, and the organic matter was mainly composed of vitrinite. The mineral composition was mainly clay minerals and brittle minerals; the clay minerals were mainly composed of kaolinite (average 11.13%) and illite/smectite mixed layers (average 26.69%) and the brittle minerals were mainly composed of quartz (average 31.63%) and feldspar (average 12.88%). (2) Eight types of lithofacies were identified, including silty mudstone, muddy siltstone, carbonaceous mudstone, carbonaceous shale, bioclastic-bearing mudstone, bioclastic-bearing sandstone, fine sandstone, and coal seam. (3) The six typical lithofacies assemblages were developed in the Longtan Formation, which represented different sedimentary environments of the marine-continental transitional facies in the study area. The lithofacies assemblages A and C represent sedimentation in the lagoon environment. The lithofacies assemblage B represents peat swamp facies. The lithofacies assemblage D represents a tidal flat facies peat flat-mixed flat-sand flat sedimentary environment. The lithofacies assemblage E and F represent the delta sedimentary environment. (4) The sedimentary model of the Longtan Formation in western Guizhou was predominantly deltaic and tidal flat sedimentary systems. Lithological and lithofacies studies of Longtan fine-grained rocks were used to provide a geological framework for examining the fine grain deposition distribution and shale gas resource evaluation. This study is highly important for understanding the sedimentology and oil and gas exploration in the region, providing a basis for identifying and exploring coal-bearing shale gas potential and a reference for the analysis of shale in the world's continental transitional areas.

Siliceous Origin of the Cambrian Qiongzhusi Formation Shale in the Middle Part of the Upper Yangtze Platform: Significance of Organic Matter Enrichment.

The early Cambrian Qiongzhusi Formation shale is rich in organic matter and is a high-quality marine Source rock. However, the origin of Qiongzhusi Formation siliceous rocks is unknown, and the role of siliceous rocks in the process of organic matter enrichment or preservation is also lacking. This study combines thin section, scanning electron microscopy, SEM/EDS, major and trace element analysis, and N2 adsorption experiments to analyze and evaluate the shale of the Qiongzhusi Formation in the central region of the Sichuan Basin. The quartz types in the shale of the Qiongzhusi Formation are divided into four types, namely, bioclastic siliceous rocks, terrestrial detrital quartz, siliceous microcrystalline quartz particles, and microcrystalline quartz aggregates; at the same time, according to petrographic and geochemical parameters, the content of authigenic quartz in Qiongzhusi Formation shale decreases from top to bottom, and terrigenous detrital quartz tends to increase, and biogenic silicon accounts for the majority of authigenic quartz components; autogenous quartz has a positive impact on the pore structure of shale, providing sufficient pore space for the development of organic pores and protecting the internal pore network by forming intergranular pores as rigid frameworks. At the same time, it plays a crucial role in the enrichment and preservation of organic matter.

Analysis of genetic diversity and genetic structure of Qinchuan cattle conservation population using whole-genome resequencing.

In the conservation of livestock and poultry resources, population genetic diversity and genetic structure of the conservation population are important factors affecting the effectiveness of conservation. In this study, whole-genome resequencing technology was used to detect genomic variation in 100 Qinchuan cattle (30 bulls and 70 cows). By analyzing population genetic diversity, runs of homozygosity (ROH) distribution features, kinship relationships, and family structure, the conservation effectiveness of Qinchuan cattle was comprehensively evaluated. The results showed that a total of 20,968,017 high-quality SNPs were detected in 100 Qinchuan cattle, the average minimum allele frequency was 0.191±0.124, the average polymorphic information content was 0.279±0.131, and the average observed heterozygosity was 0.275±0.131, the average expected heterozygosity is 0.279±0.131, indicating that the genetic diversity of the Qinchuan cattle conservation population is relatively rich. The average identity by state (IBS) distance of the Qinchuan conservation population was 0.243±0.020, with a value of 0.242±0.021 for the bulls. The results of the kinship G-matrix were consistent with the results of the IBS distance matrix, both showing that some individuals in the conservation population had close kinship. A total of 8258 genomic ROH were detected in 100 Qinchuan cattle, with a total length of 9.64 GB. The average length of ROH fragments was 1.167±1.203 Mb, 69.35% of the ROH were short ROH with a length of 0.5~1 Mb, and the average total length of ROH per individual was 96.40 Mb. The average inbreeding coefficient based on ROH was 0.039±0.039, with a value of 0.044±0.035 for the bulls, indicating that some bulls had a certain degree of inbreeding accumulation. The results of the phylogenetic tree combined with kinship analysis showed that the individuals in the Qinchuan cattle conservation population could be divided into eight families, including seven families with bulls and one family without bulls. This study demonstrated that the genetic diversity of the Qinchuan conservation population is relatively rich, with no significant inbreeding accumulation, but there is a risk of inbreeding among some individuals. Therefore, it is necessary to strengthen selection and mating to ensure the sustainable development of Qinchuan cattle resources.

M-plane GaN terahertz quantum cascade laser structure design and doping effect for resonant-phonon and phonon-scattering-injection schemes.

Non-polar m-plane GaN terahertz quantum cascade laser (THz-QCL) structures have been studied. One is traditional three-well resonant-phonon (RP) design scheme. The other is two-well phonon scattering injection (PSI) design scheme. The peak gains of 41.8 and 44.2 cm-1 have been obtained at 8.2 and 7.7 THz respectively at 300 K according to the self-consistent non-equilibrium Green's function calculation. Different from the usual GaAs two-well design, the upper and lower lasing levels are both ground states in the GaN quantum wells for the PSI scheme, mitigating the severe broadening effect for the excited states in GaN. To guide the fabrication of such devices, the doping effect on the peak gain has been analyzed. The two designs have demonstrated distinct doping density dependence and it is mainly attributed to the very different doping dependent broadening behaviors. The results reveal the possibility of GaN based THz-QCL lasing at room temperature.

Inserting self-assembled InAs quantum dots into quantum cascade lasers to achieve a broadband free-running frequency comb and effective radio-frequency injection.

We present what we belive to be a new band design in which self-assembled InAs quantum dots (QD) are embedded in InGaAs quantum wells (QW) to fabricate broadband single-core quantum dot cascade lasers (QDCLs) operating as frequency combs. The hybrid active region scheme was exploited to form upper hybrid QW/QD energy states and lower pure QD energy states, which expanded the total laser bandwidth by up to 55 cm-1 due to a broad gain medium provided by the inherent spectral inhomogeneity of self-assembled QDs. The continuous-wave (CW) output power of these devices was as high as 470 mW with optical spectra centered at ∼7 µm, which allowed CW operation at temperatures up to 45 °C . Remarkably, measurement of the intermode beatnote map revealed a clear frequency comb regime extending over a continuous 200 mA current range. Moreover, the modes were self-stabilized with intermode beatnote linewidths of approximately 1.6 kHz. Furthermore, what we believe to be a novel π-shaped electrode design and coplanar waveguide transition way were used for RF signal injection. We found that RF injection modified the laser spectral bandwidth by up to 62 cm-1. The developing characteristics indicate the potential for comb operation based on QDCLs as well as the realization of ultrafast mid-infrared pulse.

Near-Full Current Dynamic Range THz Quantum Cascade Laser Frequency Comb.

The present study proposes a terahertz quantum cascade laser frequency comb (THz QCL FC) with a semi-insulated surface plasma waveguide characterized by a low threshold current density, high power and a wide current dynamic range. The gain dispersion value and the nonlinear susceptibility were optimized based on the combination of a hybrid bound-to-continuum active region with a semi-insulated surface plasmon waveguide. Without any extra dispersion compensator, stable frequency comb operation within a current dynamic range of more than 97% of the total was revealed by the intermode beat note map. Additionally, a total comb spectral emission of about 300 GHz centered around 4.6 THz was achieved for a 3 mm long and 150 µm wide device. At 10 K, a maximum output power of 22 mW was obtained with an ultra-low threshold current density of 64.4 A·cm-2.

Changing Hydrocarbon-Producing Potential of the Cambrian Niutitang Shale: Insights from Pyrite Morphology and Geochemical Characteristics.

The characteristics of shale gas enrichment conditions at different depositional positions of organic-rich shale in the Niutitang Formation of the Lower Cambrian of the Upper Yangtze in South China vary greatly. The study of pyrite provides a basis for the restoration of the ancient environment and a reference for the prediction of organic-rich shale. In this paper, the organic-rich shale of the Cambrian Niutitang Formation in the Cengong area is analyzed by means of the optical microscope, scanning electron microscope observation, carbon and sulfur analysis, X-ray diffraction whole rock mineral analysis, sulfur isotope test, and image analysis. The morphology and distribution characteristics, genetic mechanism, water column sedimentary environment, and influence of pyrite on the preservation conditions of organic matter are discussed. This study shows that the upper, middle, and lower sections of the Niutitang Formation are rich in pyrite (framboid, euhedral pyrite, subhedral pyrite, etc.). Meanwhile, the sulfur isotopic composition of pyrite (δ34Spy) shows a tight correlation with the framboid size distribution throughout the shale deposits of the Niutang Formation, and the average particle size (9.6 µm; 6.8 µm; 5.3 µm) and distribution range of framboids (2.7-28.1 µm; 2.9-15.8 µm; 1.5-13.7 µm) in the upper, middle, and lower sections show a downward trend. In contrast, the sulfur isotopic composition of pyrite shows a tendency to become heavier from above and below (mean = 0.25‰ to 5.64‰). Together with the covariant mode of pyrite trace elements (such as Mo, U, V, Co, Ni, etc.), the results showed significant differences in the oxygen levels in the water column. They show that the transgression led to long-term anoxic sulfide conditions in the lower water column of the Niutitang Formation. In addition, the main and trace elements in pyrite jointly indicated that there was hydrothermal action at the bottom of the Niutitang Formation, which led to the destruction of the preservation environment of organic matter and the decrease of TOC, which can also explain the reason why the TOC content in the middle part (6.59%) was higher than that in the lower part (4.29%). Finally, the water column became an oxic-dysoxic condition due to the decline of sea level, and the TOC content decreased (1.79%).

Continuous-wave microcavity quantum cascade lasers in whispering-gallery modes up to 50 °C.

Micro-resonator-based lasers are well suited for high-density optoelectronic integration because of their small volumes and low thresholds. However, microcavity quantum cascade lasers for on-chip sensing have high thermal loads that make continuous-wave operation challenging. In this work, we designed an selective thermal dissipation scheme for the selective electrical isolation process to improve the thermal conductivity of the devices. The lasers operated at 50 °C, with 4.7-µm emission. They were fabricated as a notched elliptical resonator, resulting in a highly unidirectional far-field profile with an in-plane beam divergence of 1.9°. Overall, these directional-emission quantum cascade lasers pave the way for portable and highly integrated sensing applications.

High-performance quantum cascade lasers at λ ∼ 9†µm grown by MOCVD.

We demonstrate a high power InP-based quantum cascade laser (QCL) (λ ∼ 9 µm) with high characteristic temperature grown by metalorganic chemical vapor deposition (MOCVD) in this article. A 4-mm-long cavity length, 10.5-µm-wide ridge QCL with high-reflection (HR) coating demonstrates a maximum pulsed peak power of 1.55 W and continuous-wave (CW) output power of 1.02W at 293 K. The pulsed threshold current density of the device is as low as 1.52 kA/cm2. The active region adopted a dual-upper-state (DAU) and multiple-lower-state (MS) design and it shows a wide electroluminescence (EL) spectrum with 466 cm-1 wide full-width at half maximum (FWHM). In addition, the device performance is insensitive to the temperature change since the threshold-current characteristic temperature coefficient, T0, is as high as 228 K, and slope-efficiency characteristic temperature coefficient, T1, is as high as 680 K, over the heatsink-temperature range of 293 K to 353 K.

Phase-locked terahertz quantum cascade laser array integrated with a Talbot cavity.

Increasing the power of a quantum cascade laser by widening laser ridges will lead to the degradation of the beam quality because of the operation of high-order transverse modes. We report on a phase-locked array scheme of terahertz quantum cascade laser (THz QCL) utilizing Talbot effect. By adjusting the absorbing boundary width of each ridge in the array, stable operation of the fundamental supermode is realized. A five-element array shows 4 times power amplification than that of a single ridge device. Due to the large power amplification efficiency, stable mode selection, and simple fabricating process, the phase-locked array scheme is very promising to further improve the performance of THz QCL.

Monolithically integrated mid-infrared sensor with a millimeter-scale sensing range.

On-chip sensors based on quantum cascade laser technology are attracting broad attention because of their extreme compactness and abundant absorption fingerprints in the mid-infrared wavelength range. Recent continuous wave operation microcavity quantum cascade lasers are well suited for high-density optoelectronic integration because their volumes are small and thresholds are low. In this experimental work, we demonstrate a monolithically integrated sensor comprising a notched elliptical resonator as transmitter, a quantum cascade detector as receiver, and a surface plasmon structure as light-sensing waveguide. The sensor structure is designed to exploit the highly unidirectional lasing properties of the notched elliptical resonator to increase the optical absorption path length. Combined with the evanescent nature of the dielectric loaded surface plasmon polariton waveguides, the structure also ensures a strong light-matter interactions. The sensing transmission distance obtained is approximately 1.16 mm, which is about one order of magnitude improvement over the traditional Fabry-Perot waveguide. This sensor opens new opportunities for long-range and high-sensitivity on-chip gas sensing and spectroscopy.

Broad tuning range, high power quantum cascade laser at λ ∼ 7.4 µm.

In this article, we report a high power quantum cascade laser (QCL) at λ∼7.4 µm with a broad tuning range. By carefully designing and optimizing the active region and waveguide structure, a continuous-wave (CW) output power up to 1.36 W and 0.5 W is achieved at 293 K and 373 K which shows the excellent temperature stability. A high wall-plug efficiency (WPE) of 8% and 13.6% in CW and pulsed mode at 293 K are demonstrated. The laser shows a characteristic temperature T0 of 224 K and T1 of 381 K over a temperature range from 283 K to 373 K. In addition, a far field of pure zero order transverse mode and a fairly wide external cavity (EC) tuning range (280 cm-1) from 6.54 µm to 8 µm are achieved in pulsed operation. In addition, an EC single mode output power of 226 mW is obtained under CW operation at 293K.

GaSb surface grating distributed feedback interband cascade laser emitting at 3.25 µm.

A second-order distributed feedback interband cascade laser emitting at 3.25 µm was designed, grown, and fabricated. By coherent epitaxy of a GaSb cap layer instead of the conventional thin InAs cap on top of the laser structure, a high-quality surface grating was made of GaSb and gold. Enough coupling strength and a significant inter-modal loss difference were predicted according to the simulation within the framework of couple-wave theory. Lasers having 2-mm-long cavities and 4.5-µm-wide ridges with high-/anti-reflection coatings were fabricated. The continuous-wave threshold current and maximum single-mode output power were 60 mA and 24 mW at 20°C, respectively. The output power of 5 mW was still kept at 55°C. Continuous tuning free from mode hopping and high single-mode suppression ratios (>20 dB) were realized at all injection currents and heat-sink temperatures, covering a spectral range of over 20 cm-1.

Extraction-Dominated Temperature Degradation of Population Inversion in Terahertz Quantum Cascade Lasers.

Degraded population inversion (PI) at elevated temperature, regarded as an important temperature degradation factor in terahertz quantum cascade lasers (THz QCL), has hindered the widespread use of these devices. Herein, the mechanism of the temperature degradation of PI is investigated microscopically. It is demonstrated that the limited extraction efficiency of the extraction system dominates the decrease of PI at elevated temperatures. To be specific, the increased temperature brings about intense thermally activated longitudinal optical phonon scattering, leading to large amounts of electrons scattering to lower level state. In this case, the resonant-phonon extraction system is incapable of depleting all the electrons from lower level states. So even though the resonant-tunneling injection seems efficient enough to compensate the electron runoff at the upper state, the electron density at lower level state increases and the overall PI turns out lower. In addition, it is found that strong electron-ionized donor separation at high temperature can induce level misalignment, which can stagger the optimal conditions of injection and extraction. Also, the extraction efficiency gets lower as the extraction system requires accurate coupling between several energy levels.

Lateral waveguide scanner integration on surface-emitting mid-infrared lasers.

In this paper, a novel, to the best of our knowledge, monolithic non-mechanical semiconductor laser scanner in the mid-infrared (MIR) spectrum is proposed. A deflector above the active region at the substrate side is used for coupling the vertical light into a lateral substrate waveguide, which creates a chain of coherent emitters such as optical phased arrays (OPAs) for beam steering. The numerical simulation reveals that GaSb-based surface-emitting interband cascade lasers (SE-ICLs) are an excellent platform for waveguide scanner integration. Due to the hundreds of micrometers of optical path difference and the narrow gap between each emitter, an extremely high angle tuning coefficient of 0.84°/nm covering the whole 28.6° steering range is obtained. This work theoretically verifies the feasibility of integrating an OPA scanner into the GaSb-based SE-ICLs, providing a practical solution to fabricate compact steerable MIR laser sources. Note that this substrate OPA concept has strong adaptation potential to extend to even longer wavelength devices such as InP and GaAs-based quantum cascade lasers.

Pore Structure and Fractal Characteristics of Deep Shale: A Case Study from Permian Shanxi Formation Shale, from the Ordos Basin.

Pore structure has certain significance for the preservation and enrichment of shale gas. However, less attention is paid to deep shale (>3000 m) which has unique pore characteristics that distinguish it from the shallow and medium layers. In order to study the pore structure characteristics of deep shale, 10 samples of the Shanxi Formation are collected from well YP-1 within the depth of 3550-3610 m in the Fuxian block of the Ordos Basin. The pore structure characteristics of shale samples are quantitatively studied by scanning electron microscopy (SEM), low-temperature nitrogen adsorption-desorption, and high-pressure mercury injection experiments. The pore surface area (SA) and pore volume (PV) of the deep shale of Shanxi formation are low, with average values of 4.282 m2/g and 0.0126 mL/g, respectively. The content of total organic carbon (TOC) is high, which is in the high over mature stage, with undeveloped organic pores and developed microfractures. The main mineral components are clay (51.6%∼89.1%) and quartz (8%∼41.7%). By establishing the relationship between SA, PV, and TOC for quartz and clay minerals, it is found that these three parameters have little contribution to SA and PV. The pore diameter is mainly mesoporous, 2.5-4 nm and 8-11 nm. The complexity of pore structure is discussed through the fractal dimension calculated by the fractal Frenkel-Halsey-Hill (FHH) model. The pore fractal dimension D 2 (2.6240) is greater than D 1 (2.5608), and the complexity of the pore structure is greater than that of the pore surface. The fractal dimension of deep shale in Shanxi is negatively correlated with TOC content and weakly correlated with quartz and clay minerals. It shows that the mineral composition of deep shale in Shanxi Formation in the study area has little effect on pore development, and the development of microfractures is the main contribution of SA and PV.