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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., (© 2024. The Author(s).)

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.

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., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

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 N 2 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., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

We report on an index-coupled distributed feedback (DFB) quantum cascade lasers (QCLs) of high single-mode stability by using of a grating reflector (GR) to reflect effectively light of a specific wavelength. Fabrications of the QCLs were performed with λ ∕4 equivalent phase shift (EPS) or sampled Moiré grating (SMG) structure, which regulates the light intensity distribution in the cavity and coupling strength. Both EPS-GR and SMG-GR QCLs demonstrate a high emission wavelength precision and a side-mode-suppression-ratio (SMSR) of 24.5 dB at the injection current of 5 A and the pulse width of 5 μs, offering considerable output power even at the edge of the gain spectrum. Furthermore, we investigated the arrays of EPS-GR and SMG-GR QCLs with lower threshold current and higher output power by introducing semi-insulated InP (Fe) ranging from 8.25 to 8.67 μm and 8.16-8.63 μm, respectively. The present QCLs via a GR are prospective for applications requiring single-mode stability and wide tunability., (© 2023 the author(s), published by De Gruyter, Berlin/Boston.)

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.

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 .

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 (δ 34 S py ) 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%)., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

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.

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/cm 2 . 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, T 0 , is as high as 228 K, and slope-efficiency characteristic temperature coefficient, T 1 , is as high as 680 K, over the heatsink-temperature range of 293 K to 353 K.

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.

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., (© 2022 Wiley-VCH GmbH.)

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.

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 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 m 2 /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., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Distributed feedback quantum cascade lasers emitting at a wavelength of 6.12 µm are reported. Benefitted from the optimized materials epitaxy and the modified bound to continuum transition active region design along with three pairs of phonon scattering, high device performance is achieved. For a 2-mm-long, 8.4-µm-wide device, the threshold current is as low as 130 mA, the corresponding threshold current density is only 0.77 kA/cm 2 , and the optical output power is 69 mW at 20 °C in continuous wave mode. The temperature of continuous wave operation can reach 100 °C, where the optical output power is still more than 8 mW. In addition, it maintains a stable single mode operation from 20 to 100 °C without mode hopping, corresponding to a total wavelength shift of 41 nm. Such low-threshold quantum cascade lasers are highly beneficial to portable and highly integrated system sensor applications.

The marine-continental transitional shale with favorable geological conditions for shale gas accumulation and broad resource prospects is widely distributed in China, which is also well developed in the Ordos Basin. The reservoir characteristic and gas-bearing properties of the transitional Shanxi Formation shale have been studied in previous studies. However, the factors influencing the organic matter (OM) accumulation have not been well studied, which restricts shale gas exploration and development of the Shanxi Formation in the Ordos Basin. According to analyses of organic geochemistry, mineral compositions, and major and trace elements, this paper has studied the paleoenvironment characteristic and its influence on the OM accumulation of the Shanxi Formation shale. The results indicate that the OM is characterized by the high mature stage and type III kerogen while the total organic content (TOC) of Member 1 is higher than that of Member 2. From Member 1 to Member 2, the paleowater depth gradually decreases, along with a gradually relative cold and dry climate, decreasing the terrestrial influx intensity and paleoproductivity and increasing the oxygen content in the water column. For Member 1, the OM accumulation is mainly controlled by the terrestrial influx intensity and paleowater depth, and other paleoenvironment factors have an unobvious contribution to the OM accumulation. For Member 2, the OM accumulation is commonly controlled by the weak terrestrial influx, low paleoproductivity, and oxic water column, resulting in the low TOC of Member 2. This study reveals the paleoenvironment characteristic and controls on the OM accumulation of the Shanxi Formation shale, which is beneficial to the reservoir selection of the Shanxi Formation in the southeastern Ordos Basin and the understanding of the OM accumulation in other transitional shales., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

A set of high-quality marine facies organic-rich shales developed in the Lower Carboniferous Dawuba Formation, which is considered to be the main target of shale gas exploration and development in Guizhou Province. In this paper, 53 samples from Well ZY1 are selected, and the core observation data, field-emission scanning electron microscopy (FE-SEM) images, and geochemical data of these samples are analyzed. On the basis of these data, the main influencing factors of organic matter enrichment in the Dawuba Formation shale were identified and an organic matter accumulation model was established. The results show that total organic carbon (TOC) values of the Dawuba Formation in the ZY1 well vary between 1.97 and 4.11%, with high values appearing at the depths of 2796-2814 m (3.00-4.11) and 2877-2894 m (1.97-3.49). The redox-sensitive element enrichments are generally low, indicating that these samples were deposited under oxic-suboxic conditions. The micronutrients (Zn, Cu, and Ni), biological Ba (Ba XS ), and P/Al also show low values, indicating low primary productivity. The chemical index of alteration (CIA) and terrigenous clastic input index (Ti/Al) showed two obvious high-value zones, indicating that shale in the study area was affected by terrigenous inputs. Similarly, the calculation results show that Fe/Mn and Rb/K values have two abnormal data segments at the same depth. The anomaly of these data at the same depth section further suggests that the shale was affected by terrigenous input during deposition. Moreover, the terrigenous input reaches the maximum in the above TOC high-value region, and it is inferred by combining with the core observation results that the gravity flow occurs in this depth. The carbon isotope of kerogen (δ 13 C org ) ranges from -26.84 to -24.36%, indicating that the source of organic matter is likely to be terrestrial plants. This is further supported by the widespread presence of filamentous organic matter using FE-SEM, despite the low productivity and poor preservation conditions during deposition of the Dawuba Formation; the enhanced terrigenous input may have provided additional sources of organic matter for the Dawuba shale., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

A dual-wavelength quantum cascade laser (QCL) with two shallow-etched distributed Bragg reflectors is designed and fabricated. Based on a heterogeneous active region within a single waveguide, single-mode emission at 7.6μm and 8.2μm was achieved. The two wavelengths can be independently controlled by selective current injection on different regions of the device, which are electrically isolated. High optical powers of about 275mW and 218mW at room temperature were obtained for the single-mode emission at 7.6μm and 8.2μm, respectively. The presented design concept for high power, dual-wavelength switchable, mid-infrared QCLs is significant in developing miniaturized multi-species gas detection systems.

We have demonstrated a mid-wave/long-wave dual-color infrared quantum cascade detector enhanced by antenna-coupled microcavity. By optimizing the size of patches, the coupling wavelength of the antenna-coupled microcavity can be conveniently tuned to match the targeted intersubband transition energy. At 77 K, the peak responsivity of our detector is 4.1 mA/W for long wave (10.4 µm) and 0.6 mA/W for mid wave (5.8 µm), while the detectivity is 1.8×10 9 cm·Hz 1/2 /W (Jones) and 2.6×10 8 cm·Hz 1/2 /W (Jones), respectively. Compared with a reference device with a 45° multi-pass geometry, the responsivity of our detector has been increased by a factor of 9.1 for the long wave and 2.7 for the mid wave. Our results illustrate how to realize a dual-color infrared detector and improve the optoelectronic performance through the concept of antenna-coupled microcavity.

Sepiolite was modified with Al 3+ via hydrothermal reaction. The substitution amount of Al 3+ for Mg 2+ and Si 4+ located at sepiolite lattice and the influence of substitution amount on the structure, specific surface area, and surface acidity of Al-modified sepiolite were investigated. On this basis, indigo-sepiolite composite pigments were prepared by Al-modified sepiolite and indigo via grinding method to evaluate the influence of Al-modified sepiolite on the structure, bonding strength, and weather resistance of composite pigment. The crystal structure of Al-modified sepiolite had no obvious change after modification. Al 3+ mainly substituted Mg 2+ located at the octahedron of the sepiolite lattice, and the substitution amount was positively related to the dosage of Al 3+ . The specific surface area of Al-modified sepiolite decreased and the distribution of channel size became wider after Al modification. In addition, the absolute value of zeta potential decreased as well as the solid acid sites increased with the increase of Al substitution in Al-modified sepiolite. For indigo-sepiolite composite pigments, the structure of Al-modified sepiolite had no obvious change as well. The adsorption amount of indigo in composite pigment after treating by DMSO and Al content as well as weak acid amount in Al-modified sepiolite presented linear correlation, indicating that Al modification could enhance the bonding strength between indigo and Al-modified sepiolite by increasing the amount of coordinated water with Al. For indigo, Al-modified sepiolite could brighten the color and reduce the weather resistance of the prepared composite pigment. The results of this study provide a new idea and basis for regulating the structure and properties of clay and for studying the preparation of composite pigment and clay functional materials., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Chen, Geng, Zhang, Jiang, Zhai and Zhang.)

This paper presents an experimental investigation on the propagation of chemical grouting in a two-dimensional permeated fracture network with various aperture widths. As grouting engineering is often concealed in most experiments, the propagation of grout in fractures is not fully understood. The anisotropic permeability of geological masses with different aperture widths was found and has been investigated since 1960. The deflection flow effect was first found by Tian for groundwater flow in two groups of fractures with different aperture widths. Field grouting indicated that the grout propagates along a group of fractures with larger apertures that are longer while propagating a shorter distance along fractures with small apertures. This phenomenon implies a deflection for grout propagation in fractures with different aperture widths. The results of our study confirm this and indicate that there would be an anisotropy of grout propagation when the two groups of aperture widths are different. The water flow conditions also cause the difference in grout propagation length. When the aperture widths of the two groups of fractures are the same, the propagation shows symmetrical ellipse propagation. The results show the anisotropy of the grout increases as the aperture width ratio increases. This study helps in understanding the mechanism of chemical grouting in fractures with different apertures and flowing water and outlines some implications for grouting design in a fractured rock mass., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

The black shale in the upper Permian Dalong Formation is considered as an excellent source rock in the Lower Yangtze region. However, mechanisms of organic matter (OM) accumulation in such a setting are scarcely understood. Here, the characteristics of total organic carbon (TOC) and elemental geochemistry of 33 rock samples from GD1 well are systematically investigated to characterize the paleoenvironmental conditions and OM accumulation mechanisms. Results show that the lower and middle parts of Dalong Formation (section A) display high TOC contents ranging from 1.19 to 6.45% (average 3.19%), whereas the upper part (section B) exhibits medium TOC contents varying from 1.18 to 4.90% (average 2.09%). These data also elucidate that the target shales were deposited in a complex paleoenvironment with moderate to strong water-mass restriction that was characterized by warm and semiarid-semihumid paleoclimate, high biotic productivity, fluctuating plaeoredox conditions, and a relatively high sedimentary rate. Compared to the organic-rich shales from section A mainly developed under an anoxic condition, shales from section B formed in an oxic-to-dysoxic water environment exhibited a comparatively higher sedimentary rate. Moreover, among all these factors that might affect OM accumulation, the paleoredox conditions appear to be the dominant controlling factors for section A, whereas the biotic productivity, paleoredox conditions, and sedimentary rate are the main controlling factors for section B. Finally, two formation models for OM accumulation in Dalong Formation shale in the Lower Yangtze region are proposed. The "preservation model" for OM accumulation in section A emphasizes that the reducing deep-water environment, which was mainly caused by the regional sea level rise, is favorable for OM preservation. The "integrated model" for OM accumulation in section B stresses that greater biotic productivity intensifies respiratory oxygen consumption in a water column and a higher sedimentary rate can greatly shorten OM exposure time for respiration by oxygen, both of which cause OM accumulation under an oxidizing water environment. These findings also add to our knowledge that despite the oxygenated water environment during shale deposition, TOC contents are not necessarily lower., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Fractal dimension is closely related to the nanoscale pore structure of shale, and it also has an important influence on the gas content of shale. To investigate the correlation between the fractal dimension and the methane (CH₄) bearing features of shale, seven Permian shale samples were analyzed with field emission scanning electron microscopy (FE-SEM), low temperature nitrogen (N₂), carbon dioxide (CO₂) and CH₄ adsorption and on-site gas desorption experiments. Based on the N₂ adsorption and desorption data, we proposed a new method to better determine the gas adsorption stage at different relative pressure ( P / P 0 ) points in the multilayer adsorption or capillary condensation stage. On this basis, two fractal dimensions, D 1 (representing the surface roughness) and D ₂ (representing pore irregularity), were obtained. By correlating the fractal dimensions and nanoscale pore structure parameters, we found that D 1 does not correlate with the pore structure parameters except for the micropore volume. Influenced by the aggregation of porous and nonporous materials, D ₂ has a positive linear relationship with the specific surface area (SSA) and micropore volume but has a negative linear correlation with the average diameter of pores. D 1 is negatively correlated with water saturation and positively correlated with free CH₄ content. The CH₄ adsorption content is positively correlated with D ₂. By fitting the on-site desorption data, the positive correlation between the total desorbed CH₄ content and the desorbed CH₄ content in stage 2 and D ₂ was also confirmed. D ₂ better reflects the CH₄ adsorption capacity of organic-rich shale than D 1 . However, D 1 can be used to reflect the influence of shale surface properties on water saturation and to indirectly reflect the free CH₄ content in shale. The fractal dimension ( D 1 and D ₂) is a clear indicator of the total free and adsorbed CH₄ content, but cannot indicate the desorbed CH₄ content at different stages.

In this article, a InP based strain-balanced In 0.58 Ga 0.42 As/In 0.47 Al 0.53 As quantum cascade laser emitting at 7.7µm is reported. The active region is based on a slightly-diagonal bound to continuum design with 50 cascade stages and a low voltage defect Δ inj of 96 meV. By optimizing the active region and waveguide structure, the waveguide loss α w of 1.18cm -1 are obtained, which contribute to a high wall-plug efficiency (WPE) of 9.08% and low threshold current of only 1.09 kA/cm 2 in continuous-wave(CW) operation at 293K. The maximum single facet output power of 1.17W in CW operation and 2.3W in pulsed operation are measured at 293K. The narrow ridge and buried ridge structure epi-side-down-mounted on the diamond heatsink improved the heat dissipation of the device. A beam of pure zero order mode and a broad external-cavity tuning range from 7.16µm to 8.16µm are also achieved.

We report an ultralow power consumption of a quantum cascade laser (QCL) emitting at λ ∼ 4.6 µm operating in continuous-wave mode at room temperature. The ultralow power consumption is achieved by using a high gain active region and shortening the device size. For the device with a 0.5-mm-long cavity and 3.2-µm-wide ridge, the threshold power consumption is as low as 0.26 W with an optical output power of 12.6 mW at 10 °C in continuous-wave mode, which represents the world's most advanced level. Furthermore, the threshold power consumption varies linearly with the operating temperature, where the linear change rate of 2.3 mW/K from 10 to 40 °C is low. As a result, the devices also show low threshold power consumption values of 0.33 W even at 40 °C in continuous-wave mode with an optical output power of 6.1 mW. In addition, the lasers can maintain a single-mode operation due to the short cavity length even if no distributed feedback grating is applied.

Effectively restraining random fluctuation of layer thickness (RFT) during the thin-film epitaxy plays an essential part in improving the quality of low-dimensional materials for device application. While it is already challenging to obtain an ideal growth condition for thickness control, the tangle of RFT with interfacial problems makes it even more difficult to guarantee the properties of heterostructures and the performance of devices. In our research, the RFT of potential barriers and wells within a semiconductor multilayer is demonstrated to correlate with the interfacial grading effect (IFG) and to affect the band offset strongly. Then, the synergetic effect of RFT and IFG that serves as the first domino is shown to impact the subband structure and the electron transport successively. On the basis of an investigation of a quantum cascade structure, statistical results indicate a normal distribution of RFT with a standard deviation of about 1 Å and an extreme value of 3 Å (about one monolayer) for all the layers within 38 cascade periods. The "seemingly negligible" RFT could actually reduce the conduction band offset for tens to hundreds of meV and alter the subband gaps at a rate of 40 meV/monolayer at most. Furthermore, the dependence of different subband gaps on the barrier/well thickness differs from one another. In addition, the distribution of wave function could also be regulated dramatically by RFT to change the type of electron transition and thus the carrier lifetime. Further impacts of RFT and the RFT-modulated subband alignment on electron transport result in two different mechanisms (injection-dominant and extraction-dominant) of electron population inversion (PI), which is manifested by comparatively discussing the results of in situ electron holography and macro performances.

This article experimentally demonstrates that the relative intensity noise (RIN) of a mid-infrared quantum cascade laser is insensitive to the optical feedback for feedback ratios up to 31% (-5.1 dB). The RIN of the free-running laser is in the range of -150 dB/Hz to -160 dB/Hz, while the optical feedback induced RIN variation is less than ± 2.0 dB. In addition, the feedback-induced lasing frequency variation is less than 2.0 GHz. Rate equation analyses of the laser are in good agreement with the experimental observations.

Mid-infrared (MIR) room-temperature (RT) and continuous-wave (CW) broadband quantum cascade superluminescent light emitters (QCSLEs) have emerged as ideal broadband light sources for a number of applications of biomedical imaging, security inspection, and gas detection. It is quite challenging to attain a RT-CW output power up to milliwatt level due to the very low efficiency of the spontaneous emission in the intersubband transitions in QCSLEs. In this work, for the first time to the best of our knowledge, a compact light emitter array is realized by integrating several single emitters exhibiting a very high RT-CW power of 2.4 mW, which is attributed to the sufficient low reflectivity provided by the waveguide structure that includes three sections with a short straight part adjacent to a tilted stripe and to a J-shaped waveguide, and the two-phonon resonance QC active structure. This advancement is certainly a big step forward to the applications of broadband light sources towards MIR photonics.

The realization of room-temperature (RT) mid-infrared (MIR) broadband light sources is fundamentally interesting and highly desirable for a number of applications. Recently, superluminescent light emitters (SLEs) based on quantum cascade (QC) structures have emerged as excellent candidates among mid-infrared broadband light sources. However, it is challenging to achieve RT-QCSLEs due to the very low efficiency of the spontaneous emission in the intersubband transitions. Here, we demonstrate the realization of a set of ~5 μm RT-SLEs under continuous wave (CW) or quasi-CW (10% duty circle) operation by using a two-phonon resonant QC active region and monolithic integrated waveguide structures. In addition, with the design of an inclined tapered cavity, the SLEs exhibit high milliwatt power, large spectral width of more than 200 cm -1 and good temperature characteristic. These demonstrated results are believed to be a big step forward to the applications of broadband MIR semiconductor light sources.

A consensus has been reached through previous studies that organic matter (OM) pores are crucial to porosity in many shale gas reservoirs; however, their origins and types remain controversial. Here, we report the OM pore types hosted in algae, bitumen, graptolite and other fossil fragments in the Wufeng-Longmaxi Formations of the Sichuan Basin, Southwest China. Algae types mainly include multicellular algae, unicellular algae, etc. The OM pores in multicellular algae usually exhibit irregular, bubble-like, spherical and/or elliptical profiles, and their diameters vary between 300 and 800 nm. The shapes of the OM pores in unicellular algae are either irregular or oval, and the pores are hundreds of nanometres in size. The pores associated with solid bitumen are sporadic, isolated and variable in size, ranging from 500 nm to 3 μm. The pores in the graptolite, sponge spicule, radiolarian and other fossil fragments are much smaller and fewer. The pores may only have developed in the surface of the graptolite and bitumen by filling in the biological cavity of the sponge spicule. These new findings provide stronger evidence that multicellular algae are the main hydrocarbon generating organisms of OM pores development.

We show a phase-locked array of three quantum cascade lasers with an integrated Talbot cavity at one side of the laser array. The coupling scheme is called diffraction coupling. By controlling the length of Talbot to be a quarter of Talbot distance (Z t /4), in-phase mode operation can be selected. The in-phase operation shows great modal stability under different injection currents, from the threshold current to the full power current. The far-field radiation pattern of the in-phase operation contains three lobes, one central maximum lobe and two side lobes. The interval between adjacent lobes is about 10.5°. The output power is about 1.5 times that of a single-ridge laser. Further studies should be taken to achieve better beam performance and reduce optical losses brought by the integrated Talbot cavity.