Search

Abstract High-power terahertz (THz) quantum cascade laser, as an emerging THz solid-state radiation source, is attracting attention for numerous applications including medicine, sensing, and communication. However, due to the sub-wavelength confinement of the waveguide structure, direct beam brightness upscaling with device area remains elusive due to several mode competition and external optical lens is normally used to enhance the THz beam brightness. Here, we propose a metallic THz photonic crystal resonator with a phase-engineered design for single mode surface emission over a broad area. The quantum cascade surface-emitting laser is capable of delivering an output peak power over 185 mW with a narrow beam divergence of 4.4° × 4.4° at 3.88 THz. A high beam brightness of 1.6 × 107 W sr−1m−2 with near-diffraction-limited M2 factors of 1.4 in both vertical and lateral directions is achieved from a large device area of 1.6 × 1.6 mm2 without using any optical lenses. The adjustable phase shift between the lattices enables a stable and high-intensity surface emission over a broad device area, which makes it an ideal light extractor for large-scale THz emitters. Our research paves the way to high brightness solid-state THz lasers and facilitates new applications in standoff THz imaging, detection, and diagnosis.

Abstract 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.

The photonic crystal surface-emitting laser (PCSEL) has attracted much attention due to the advantages of a small far-field divergence angle and high output power. Here, we report a high-power terahertz (THz) photonic crystal laser with high beam quality through the optimization of the absorption boundary condition and the introduction of the symmetrically distributed electrodes. Single-mode surface emission at 3.4 THz with the maximum peak output power of 50 mW is demonstrated. Meanwhile, a high symmetric far-field pattern with C6 symmetry and a small divergence angle is achieved. In this device, the integration of the stable single-mode operation, high beam quality and high output power is realized, which may have great significance for practical applications.

In this research, we demonstrate a wavelength-stable continuous wave (CW) distributed feedback (DFB) quantum cascade laser (QCL) emitting at 7.2 μm using a surface metal grating approach without epitaxial regrowth. The deep metal grating provides an appropriate DFB coupling coefficient and enhanced thermal extraction, resulting in improved lasing performance and the realization of impressive wavelength stability. Quantitatively, the temperature tuning coefficient of the single-mode emission is only 0.54 nm/°C from 20 °C to 70 °C, and the current tuning coefficient of the single-mode emission is 3.2 nm/A from 1.0 A to 1.6 A. A DFB-QCL with a 2 mm cavity length exhibits a low threshold current of 0.6 A and a power of 1.1 W with a slope efficiency of 1 W/A in the CW mode at 300 K. A single-mode operation with a side mode suppression ratio of 33 dB and a single-lobed far-field without beam steering is obtained in the working temperature range of 20–70 °C The improved wavelength stability using a deep surface metal grating approach promises simplified fabrication, which is meaningful for the commercial applications of QCLs.

BACKGROUND Human health risks and potential environmental geological hazards caused by contaminated sites have been paid much attention. Monitored natural attenuation (MNA) is recognized as a preferred remediation technique. However, for sites with non-aqueous phase liquids (NAPLs), the problem of "tailing rebound" caused by the residue of NAPLs in the source area poses a challenge to the MNA technology. In recent years, the emergence of natural source zone depletion (NSZD) enriches the connotation of MNA remediation, and it is a potential way to solve the problem of "Tailing & Rebound". OBJECTIVES To summarize the research process and latest achievements of NSZD for light non-aqueous phase liquid (LNAPL) contaminated sites. METHODS A comprehensive review was conducted on the literature on NSZD for LNAPL contaminated sites from the end of the 1990's. The conceptual models of vertical zoning natural elimination in LNAPL source areas have been reviewed. The key control factors on NSZD and main scientific and technological challenges for future research have been fully discussed. RESULTS The research shows that: (1) since 2000, the research on MNA remediation has gradually shifted from groundwater pollution plume attenuation to natural depletion of vadose zone source areas; (2) The natural elimination process of aeration zones has proved to be the key biological process of NSZD, accounting for 90%-99% of the total mass loss of LNAPLs; (3) biodegradation in the volatilization process of LNAPL is the major research field of NSZD. The following research methods of NSZD are established: (1) the NSZD method can be divided into three parts: LNAPL source area plume identification, qualitative judgment and quantitative estimation; (2) The Concentration Gradient Method, CO2 Fluxes Method (including Dynamic Closed Chambers and CO2 Traps) and Thermal Gradient Method are three major methods for quantitative estimation. CONCLUSIONS Based on the existing research progress and challenges, the key scientific problems to be solved in the application and promotion of NSZD include identifying the composition change of LNAPLs in the source area, clarifying the speed limiting factor for natural elimination in the source area, and developing appropriate monitoring methods for degassing and bubble escape.

Petroleum hydrocarbons (PHCs) can be biodegraded into CO2, and PHC‐contaminated aquifers are always deemed as carbon sources. Fortunately, some carbon fixation microorganisms have been found in PHC‐contaminated sites. However, most of the studies are related to volatile short‐chain PHC, and few studies focus on long‐chain PHC‐contaminated sites. To reveal the carbon fixation microorganisms in these sites, in the study, a long‐chain PHC polluted site in North China was selected. Through hydrochemical and metagenomics analysis, the structure and capacity of carbon fixing microorganisms in the site were revealed. Results showed that there were many kinds of carbon fixed microorganisms that were identified such as Flavobacterium, Pseudomonas. HP/4HB, rTCA, and DC/4HB cycles were dominated carbon fixation pathways. The long‐chain PHC were weakly correlated with carbon fixation microorganisms, but it may stimulate the growth of some carbon fixation microorganisms, such as microorganisms involved in rTCA cycle. Practitioner Points: The microorganisms with carbon fixation gene exist in the aquifer contaminated by long‐chain petroleum hydrocarbon.Microorganisms that have the ability to degrade petroleum also have the ability to carbon fixation.Long‐chain petroleum hydrocarbon may promote the growth of carbon fixation microorganisms. [ABSTRACT FROM AUTHOR]

Microorganisms in groundwater at petroleum hydrocarbon (PHC)‐contaminated sites are crucial for PHC natural attenuation. Studies mainly focused on the microbial communities and functions in groundwater contaminated by PHC only. However, due to diverse raw and auxiliary materials and the complex production processes, in some petrochemical sites, groundwater suffered multi‐component contamination, but the microbial structure remains unclear. To solve the problem, in the study, a petrochemical enterprise site, where the groundwater suffered multi‐component pollution by PHC and sulfates, was selected. Using hydrochemistry, 16S rRNA gene, and metagenomic sequencing analyses, the relationships among electron acceptors, microbial diversity, functional genes, and their interactions were investigated. Results showed that different production processes led to different microbial structures. Overall, pollution reduced species richness but increased the abundance of specific species. The multi‐component contamination multiplied a considerable number of hydrocarbon‐degrading and sulfate‐reducing microorganisms, and the introduced sulfates might have promoted the biodegradation of PHC. Practitioner Points: The compound pollution of the site changed the microbial community structure.Sulfate can promote the degradation of petroleum hydrocarbons by hydrocarbon‐degrading microorganisms.The combined contamination of petroleum hydrocarbons and sulfates will decrease the species richness but increase the abundance of endemic species. [ABSTRACT FROM AUTHOR]

IntroductionSerum albumin levels at a single time point have been shown to predict mortality in peritoneal dialysis (PD) patients. However, we believe that the dynamic change in albumin after PD may be more significant. In this study, we investigated the relationship between dynamic serum albumin and the clinical outcome of patients undergoing continuous ambulatory peritoneal dialysis (CAPD).MethodsThe participants in this study enrolled 586 patients who underwent CAPD at the peritoneal dialysis center of Second Xiangya Hospital in China. We retrospectively reviewed medical records from January 1, 2010, to December 31, 2019. Baseline serum albumin (Alb), time-averaged albumin level (TA-ALB) and serum albumin reach rate (SR: defined as the percentage of serum albumin measurements that reached ≥ 35 g/L) were applied as the predictor variables. All-cause mortality and cardiovascular mortality were used as the outcome variables. Hazard function of all-cause mortality and cardiovascular mortality in the study participants were examined by using Cox proportional hazard regression models.ResultsAge (HR = 1.03, 95% CI 1.00–1.05), cardiovascular disease (HR = 1.80, 95% CI 1.07–3.03) and TA-ALB (HR = 0.92, 95% CI 0.85–0.99) were independent risk factors for all-cause mortality in PD patients. Patients with TA-ALB of

ObjectiveThe number of elderly patients on peritoneal dialysis (PD) has rapidly increased in the past few decades. We sought to explore the microbiology and outcomes of peritonitis in elderly PD patients compared with younger PD patients.MethodsWe conducted a retrospective study to analyze the clinical characteristics, causative organism distribution, and outcome of all PD patients who developed peritonitis between September 1, 2014 and December 31, 2020, from Second Xiangya Hospital, Central South University, China. Patients who experienced peritonitis were separated into elderly and younger groups. The elderly was defined as ≥ 65 years old at the initiation of PD.ResultsAmong 1,200 patients, 64(33.9%) in elderly (n = 189) and 215 (21.3%) in younger (n = 1,011) developed at least one episode of peritonitis. A total of 394 episodes of peritonitis occurred in 279 patients. Of these, 88 episodes occurred in 64 elderly patients, and 306 episodes occurred in 215 younger patients. Gram-positive bacteria were the main causative organisms in elderly and younger patients (43.2% and 38.0%, respectively). Staphylococcus and Escherichia coli were the most common gram-positive and gram-negative bacteria, respectively. Fungal peritonitis in elderly patients was higher compared with younger patients (χ2 = 6.55, P = 0.01). Moreover, Acinetobacter baumannii (χ 2=9.25, P = 0.002) and polymicrobial peritonitis (χ 2 = 6.41, P = 0.01) in elderly patients were also significantly higher than that in younger patients. Additionally, elderly PD patients had higher peritonitis-related mortality than younger patients (χ 2 = 12.521, P = 0.000), though there was no significant difference in catheter removal between the two groups. Kaplan-Meier analysis showed that cumulative survival was significantly lower in elderly patients than younger patients (log rank = 7.867, p = 0.005), but similar technical survival in both groups (log rank = 0.036, p = 0.849).ConclusionsThis retrospective study demonstrated that elderly PD patients were more likely to develop Acinetobacter baumannii, fungal and polymicrobial peritonitis than younger PD patients. In addition, peritonitis-related mortality was significantly higher in elderly patients, whereas peritonitis-related catheter removal was comparable between elderly and younger PD patients. Understanding microbiology and outcome in elderly patients will help to reduce the incidence of PD-associated peritonitis and improve the quality of life.

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.

In this article, we report a high-performance λ ~ 4.6 μm quantum cascade laser grown by metal-organic chemical vapor deposition. Continuous wave power of 3 W was obtained from an 8 mm-long and 7.5 μm wide coated laser at 285 K. The maximum pulsed and CW wall-plug efficiency reached 15.4% and 10.4%, respectively. The device performance shows the great potential of metal-organic chemical vapor deposition growth for quantum cascade material and devices.

Abstract A high‐speed, room‐temperature quantum cascade laser packaged module emitting at 8.14 μm is presented. The cavity length of the laser is as small as 0.5 mm, and the threshold current at 298 K is 110 mA. A matching printed circuit board is inserted into the packaged module to reduce the RC constant. As a result, the rectification response of packaged module is relatively flat upto 2 GHz and the –3 dB cut‐off frequency is increased from 0.9 to 2.2 GHz.

A typical interband cascade laser wafer contains more than 2000 multilayers composed of InAs, AlSb, GaSb, and GaInSb. The lattice constants of the three materials except GaSb have a certain degree of mismatch with the GaSb substrate. Therefore, to grow a high-quality epitaxial layer, it is necessary to optimize the growth conditions to achieve strain balance in the entire epitaxial layer. In this work, the strained superlattice structure was characterized via scanning transmission electron microscopy and high-resolution x-ray diffraction. The strain distribution was mapped using geometric phase analysis of high-angle annular dark-field images. We demonstrate that strain compensation has been achieved in both the InAs/AlSb superlattice clad layers and the InAs/InGaSb/InAs W quantum well active region.

Abstract In this paper, an anomalous spectral data of distributed Bragg reflector (DBR) quantum cascade lasers (QCLs) emitting around 7.6 μm is presented. The two-section DBR lasers, consisting of a gain section and an unpumped Bragg reflector, display an output power above 0.6 W in continuous wave (CW) mode at room temperature. The anomalous spectral data is defined as a longitudinal mode which moves toward shorter wavelengths with increasing temperature or injection current, which is unexpected. Although the longer wavelength modes are expected to start lasing when raising device temperature or injection current, occasional mode hops to a shorter wavelength are seen. These anomalous mode transitions are explained by means of modal analysis. The thermal-induced change of the refractive index implied by an increase in the temperature or injection current yields nearly periodic transitions between cavity modes.

Immunoglobulin G4-related disease (IgG4-RD) is an autoimmune inflammatory disease characterized by infiltration of IgG4+ plasma cells that can simulate a tumor manifesting as a tumor-like mass. This disease involves the pancreas, biliary tract, kidneys, salivary glands, lymph nodes, aorta, and retroperitoneum amongst other organs. However, testicular involvement is a rare entity in this disease. The treatment of testicular involvement in IgG4-RD is currently controversial. We present the case of a 65-year-old man with swelling and pain in his right scrotum three months ago. On examination, a mobile mass of approximately 2 cm in diameter was found in the right scrotum. Serological tests showed elevated levels of IgG4 and negative for tumor markers. Enhanced computed tomography of the scrotum showed a nodular hyperdense shadow with a diameter of approximately 23 mm on the right epididymis. Pathological biopsy of the right epididymis showed infiltration of plasma cells, lymphocytes, and a few neutrophils. IgG4+ plasma cells stained positive, with an IgG4/IgG ratio of more than 40% and more than 30 IgG4+ plasma cells per high-power field. A diagnosis of IgG4-RD involving the testicles was made. Prednisone 30 mg/d was given for three weeks. No scrotum swelling or pain was observed at the follow-up after six months. IgG4-related disease should be considered whenever a mass-like lesion with typical histomorphologic features involving multiple organs/anatomical sites is encountered. The testicles are an important male reproductive organ, especially for young male patients with fertility requirements. For patients with IgG4-RD testicular involvement, surgical or medical treatment requires further study.

Abstract High-power, low-threshold stable single-mode operation buried distributed feedback quantum cascade laser by incorporating sampled grating emitting at λ ~ 4.87 μm is demonstrated. The high continuous wave (CW) output power of 948 mW and 649 mW for a 6-mm and 4-mm cavity length is obtained at 20 °C, respectively, which benefits from the optimized optical field distribution of sampled grating. The single-mode yields of the devices are obviously enhanced by controlling cleaved positions of the two end facets precisely. As a result, stable single-mode emission and mode tuning linearly without any mode hopping of devices are obtained under the different heat sink temperatures or high injection currents.

Abstract We present a low threshold-current and fast wavelength-tuning external cavity quantum cascade laser (EC-QCL) using a scanning galvanometer in the Littman-Metcalf cavity geometry. The EC-QCL could repeatedly swept at 100 Hz over its full tuning range of about 290 nm (2105 cm−1 to 2240 cm−1), providing a scan rate of 59.3 μm s−1. The continuous-wave (CW) threshold current of the EC-QCL was as low as 250 mA and the maximum output power was 20.8 mW at 400 mA for a 3-mm-long QCL gain chip. With a sawtooth wave modulation, a scan resolution of

We have demonstrated a room temperature, low power consumption, high-speed, and single-mode tunable quantum cascade laser at λ ∼ 4.6 µm. Combining a 300 µm buried hetero-structure ultra-short cavity with optimized facet coatings, a single-mode tuning range covering ∼40 nm is obtained at room temperature under low electrical power consumption below 1.1 W. The single-mode emission is observed with more than 25 dB side mode suppression ratio in the whole tuning range. The high frequency modulation is achieved with a microwave package, resulting in the −3 dB cutoff frequency of 5.6 GHz.

Abstract Power scaling in broad area quantum cascade laser (QCL) usually leads to the deterioration of the beam quality with an emission of multiple lobes far-field pattern. In this letter, we demonstrate a tapered QCL array integrated with Talbot cavity at one side of the array. Fundamental supermode operation is achieved in the arrays with taper straight-end connected to the Talbot cavity. Lateral far-field of the fundamental supermode shows a near diffraction limited beam divergence of 2.7°. The output power of a five-element array is about three times as high as a single-ridge laser with an emission wavelength of around 4.8 μm. However, arrays with the taper-end connected to the Talbot cavity always show a high-order supermode operation whatever Talbot cavity length is.

Abstract In this work, quantum cascade lasers (QCLs) based on strain compensation combined with two-phonon resonance design are presented. Distributed feedback (DFB) laser emitting at ~ 4.76 μm was fabricated through a standard buried first-order grating and buried heterostructure (BH) processing. Stable single-mode emission is achieved under all injection currents and temperature conditions without any mode hop by the optimized antireflection (AR) coating on the front facet. The AR coating consists of a double layer dielectric of Al2O3 and Ge. For a 2-mm laser cavity, the maximum output power of the AR-coated DFB-QCL was more than 170 mW at 20 °C with a high wall-plug efficiency (WPE) of 4.7% in a continuous-wave (CW) mode.

Abstract In the present work, an ultra-low power consumption substrate-emitting distributed feedback (DFB) quantum cascade laser (QCL) was developed. The continuous-wave (CW) threshold power dissipation is reduced to 0.43 W at 25 °C by shortening the cavity length to 0.5 mm and depositing high-reflectivity (HR) coating on both facets. As far as we know, this is the recorded threshold power dissipation of QCLs in the same conditions. Single-mode emission was achieved by employing a buried second-order grating. Mode-hop free emission can be observed within a wide temperature range from 15 to 105 °C in CW mode. The divergence angles are 22.5o and 1.94o in the ridge-width direction and cavity-length direction, respectively. The maximum optical power in CW operation was 2.4 mW at 25 °C, which is sufficient to spectroscopy applications.