Loss-tailoring single-mode high-power supersymmetric lasers.

Diode lasers with high beam quality and high power have many promising applications. However, high beam quality is always in conflict with high power. In this Letter, we theoretically and experimentally confirm the mode instability property of supersymmetric structures at higher operating currents. Meanwhile, we propose a loss-tailoring diode laser based on a supersymmetric structure, which enables the higher-order lateral modes to obtain higher losses, raises the excitation threshold of the higher-order lateral modes, and achieves a stable fundamental-lateral-mode output at higher current operation. The device obtained a quasi-single-lobe lateral far-field distribution with the full width at half maximum (FWHM) of 7.58° at 350 mA under room temperature, which is a 65% reduction compared to the traditional Fabry-Perot (FP) diode lasers. Moreover, the M2 of 2.181@350 mA has an improvement of about 37% over traditional FP and supersymmetric structure lasers.

Electrically driven supersymmetric semiconductor laser arrays with single-lobe far-field patterns.

Semiconductor laser arrays based on the third-order supersymmetric (SUSY) transformation are proposed to increase the mode discrimination between fundamental supermode and high-order supermodes. The distance between the edge waveguide of the main array and that of the superpartners is optimized. Then, the electric field distributions of different modes are also calculated, which show that, except for the fundamental supermode, the high-order supermodes penetrate deeper into the superpartner arrays, which accounts for the increased loss of high-order supermodes. The fabricated third-order SUSY laser array can emit light with a single-lobe far-field pattern under an injection current of 70 mA, which is a promising candidate for optical couplings between lasers and optical elements.

Optimized performance of 905†nm semiconductor lasers by using the high strain quantum well.

We propose and experimentally demonstrate that the lasing power and characteristic temperature (T0) of 905 nm semiconductor lasers can be optimized by use of the high strain quantum well (HSQW). To fix the lasing wavelength around 905 nm, HSQW with a higher ndium (In) content of the InGaAs gain material than that of the commonly used low strain quantum well (LSQW) requires a thickness-reduced quantum well. Thus, the HSQW has the following two advantages: stronger quantum size effects caused by the deep and thin quantum well, and higher compressive strain caused by a high In content of the InGaAs gain material. With the similar epitaxial structure, laser diodes with HSQW have a characteristic temperature T0 of 207 K and can deliver a higher lasing power with less power saturations. The high strain quantum well optimization method can be extended to other laser diodes with a wavelength near 900 nm with low In content InGaAs quantum wells and other similar low-strain gain material systems.

Doping profile architecture towards lower loss and higher efficiency for laser diodes.

A doping optimization model towards lower loss and higher efficiency at the target operating current is investigated. This model considers the effect of doping concentration on the series resistance and the internal loss. 780 nm lasers doped with a normal doping profile (Dop_normal) and an optimized doping profile (Dop_optimize) are both designed and fabricated. After doping optimization, the power loss decreased by 17%, the output power of the lasers increased by 26% and the electro-optical conversion efficiency increased by 22%. The model provides significant theoretical guidance for the optimization of the laser doping.

High-efficiency spectral beam combining of an individual laser diode bar with polarization multiplexing.

In this Letter, a new strategy for the spectral beam combining (SBC) of an individual laser diode (LD) bar based on a polarization multiplexing external cavity is proposed and demonstrated. The maximum combining efficiency is up to 95.51%, which leads to an output power of 76.6 W and an electro-optic conversion efficiency of 48.33% under continuous wave operation at a current of 100 A. Compared to the conventional SBC, the combining efficiency, the output power, and the electro-optical conversion efficiency present improvements of 12%, 10W, and 6%, respectively. The results show that this novel SBC method is a prospective technique for increasing the combining efficiency of LD bars.

Theoretically Revealed and Experimentally Demonstrated Synergistic Electronic Interaction of CoFe Dual-Metal Sites on N-doped Carbon for Boosting Both Oxygen Reduction and Evolution Reactions.

Heteronuclear double-atom catalysts, unlike single atom catalysts, may change the charge density of active metal sites by introducing another metal single atom, thereby modifying the adsorption energies of reaction intermediates and increasing the catalytic activities. First, density functional theory calculations are used to figure out the best combination by modeling two transition-metal atoms from Fe, Co, and Ni onto N-doped graphene. Generally, Fe and Co sites are highly active for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), respectively. The combination of Co and Fe to form CoFe-N-C not only further improves the Fe's ORR and Co's OER activities but also greatly enhances the Co site's ORR and Fe site's OER activities. Then, we synthesize the CoFe-N-C by a two-step pyrolysis process and find that the CoFe-N-C exhibits exceptional ORR and OER electrocatalytic activities in alkaline media, significantly superior to Fe-N-C and Co-N-C and even commercial catalysts.

Exploiting the Synergistic Electronic Interaction between Pt-Skin Wrapped Intermetallic PtCo Nanoparticles and Co-N-C Support for Efficient ORR/EOR Electrocatalysis in a Direct Ethanol Fuel Cell.

The development of low-Pt catalysts with high activity and durability is critical for fuel cells. Here, Pt-skin wrapped sub-5 nm PtCo intermetallic nanoparticles are successfully mounted on single atom Co-N-C support by exploiting the barrier effect of Co-anchor. According to a collaborative experimental and computational investigation, the increased oxygen reduction reaction activity of PtCo/Co-N-C arises from the direct electron transfer from PtCo to Co-N-C, and the resulting optimal d-band center of Pt. Owing to such unique electronic structure interaction and synergistic effect, the specific and mass activities of PtCo/Co-N-C are up to 4.20 mA cm-2 and 2.71 A mgPt-1 , respectively, with barely degraded stability after 40 000 CV cycles. The PtCo/Co-N-C also exhibits outstanding activity as an ethanol electrocatalyst. This work shows a new and effective route to boost the overall efficiency of direct ethanol fuel cells in acidic media by integrating intermetallic low-Pt alloys and single atom carbon support.

High-power laser diode at 9xx nm with 81.10% efficiency.

In this study, a low-resistance, low-loss, continuously gradual composition extreme double asymmetric (CGC-EDAS) epitaxial structure is designed to improve efficiency. The structure and facet reflectivity of the broad area (BA) lasers are optimized to maximize the power conversion efficiency (PCE). In the experiment, the peak PCE of 75.36% is measured at 25°C. At 0°C, a peak PCE of 81.10% is measured and the PCE can still reach 77.84% at an output power of 17.10 W, which, to the best of our knowledge, is the highest value to date for any BA lasers.

High-power tunable dual-wavelength diode laser with a composite external cavity.

A high-power tunable dual-wavelength composite external cavity architecture obtained by means of a holographic grating and a volume Bragg grating is proposed and demonstrated. The tunable frequency difference of the dual-wavelength output is from 0.41 THz to 3.89 THz. We obtain an output power of 2.1 W when the frequency difference is 1.86 THz. The side-mode suppression ratio of more than 29 dB is suppressed over the entire tunable dual-wavelength output range. The two corresponding wavelengths of the dual-wavelength output basically maintain the same intensity with the smallest power difference of only 0.10%.

High-brightness and high-efficiency diode laser module based on double wavelength division multiplexing external cavities.

In this Letter, a new, to the best of our knowledge, external cavity structure based on double wavelength division multiplexing external cavities is proposed and demonstrated. The electro-optical conversion efficiency is improved and the brightness of the spectral beam combining diode lasers is enhanced. One wavelength division multiplexing external cavity is placed on the rear-side of the laser emitters to provide the strong optical feedback for wavelength locking and the other wavelength division multiplexing external cavity is placed on the front-side of laser emitters to combine three emitter beams to one beam. A maximum output power of up to 7.5 W is obtained and the brightness of the laser diode is 100 MW cm-2 sr-1 with an electro-optical conversion efficiency of 46.5%. Compared with a standard cavity for spectral beam combining, the use of double wavelength division multiplexing external cavities results in an electro-optical conversion efficiency improvement of 6.5%. The whole structure provides a new technology to achieve high-brightness and high electro-optical conversion efficiency for a laser diode source.

Electrically injected supersymmetric semiconductor lasers with narrow vertical divergence angle.

Electrically injected supersymmetric (SUSY) semiconductor lasers are proposed and fabricated. Two successive SUSY transformations are applied to the main array arranged along the direction of epitaxial growth, which can remove the propagation constants of the fundamental mode and the leaky mode of the main array from the superpartner while keeping those of other high-order modes. The SUSY laser possesses an excellent mode discrimination and favors the lasing of the fundamental mode. The fabricated SUSY laser can emit light with a single-lobe vertical far-field pattern with the full width at half maximum of 16.87° under an injection current of 1.4 A.

Approaches to tuning the exceptional point of PT-symmetric double ridge stripe lasers.

Electrically injected Parity-time (PT)-symmetric double ridge stripe semiconductor lasers lasing at 980 nm range are designed and measured. The spontaneous PT-symmetric breaking point or exceptional point (EP) of the laser is tuned below or above the lasing threshold by means of varying the coupling constant or the mirror loss. The linewidth of the optical spectrum of the PT-symmetric laser is narrowed, compared with that of traditional single ridge (SR) laser and double ridge (DR) laser. Furthermore, the far field pattern of the PT-symmetric laser with EP below the lasing threshold is compared with that of the PT-symmetric laser with EP above the lasing threshold experimentally. It is found that when the laser start to lase, the former is single-lobed while the latter is double-lobed. when the current continues to increase, the former develops into double lobe directly while the latter first develops into single lobe and then double lobe again.

Rhomboid intercostal block combined with sub-serratus plane block versus rhomboid intercostal block for postoperative analgesia after video-assisted thoracoscopic surgery: a prospective randomized-controlled trial.

BACKGROUND: Rhomboid intercostal block (RIB) and Rhomboid intercostal block with sub-serratus plane block (RISS) are the two types of plane blocks used for postoperative analgesia after video-assisted thoracoscopic surgery (VATS). This prospective randomized controlled trial was performed to analyze the postoperative analgesic effects of ultrasound-guided RIB block and RISS block after video-assisted thoracoscopic surgery. METHODS: Ninety patients aged between 18 and 80 years, with American Society of Anesthesiologists physical status Classes I-II and scheduled for elective unilateral VATS were randomly allocated into three groups. In group C, no block intervention was performed. Patients in group RIB received ultrasound-guided RIB with 20-mL 0.375% ropivacaine and those in group RISS received ultrasound-guided RIB and serratus plane block using a total of 40-mL 0.375% ropivacaine. All patients received intravenous sufentanil patient-controlled analgesia upon arrival in the recovery room. Postoperative sufentanil consumption and pain scores were compared among the groups. RESULTS: The dosages of sufentanil consumption at 24 h after the surgery in the RIB and RISS groups were significantly lower than that in group C (p < 0.001 and p < 0.001 for all comparisons, respectively), the postoperative Numerical Rating Scale (NRS) scores in the RIB and RISS groups at 0.5, 1, 3, 6, 12, 18, and 24 h after surgery when patients were at rest or active were significantly lower than that in group C (p < 0.05 for all comparisons). The required dosage of sufentanil and time to first postoperative analgesic request in groupRISS were less than those in the group RIB at 24 h after the surgery (p < 0.001 and p < 0.001 for all comparisons, respectively). Similarly, the Numerical Rating Scale scores for group RISS at 12, 18, and 24 h after the surgery when the patients were active were significantly lower than those for group RIB (p < 0.05 for all comparisons). CONCLUSION: Both ultrasound-guided RIB block and RISS block can effectively reduce the demand for sufentanil within 24 h after VATS, and less sufentanil dosage is needed in patient with RISS block. Ultrasound-guided RIB block and RISS block can effectively relieve pain within 24 h after VATS, and RISS block is more effective.

Dexmedetomidine in the prevention of postoperative delirium in elderly patients following non-cardiac surgery: A systematic review and meta-analysis.

The efficacy of dexmedetomidine in the prevention of postoperative delirium (POD) remains ambiguous, however, it has been used to reduce the incidence of delirium in elderly patients. Here, we conducted a meta-analysis study for assessing the effects of dexmedetomidine on POD among elderly patients following non-cardiac surgery. A systematic literature search was performed against the PubMed, EMBASE, Cochrane Library, and Web of Science databases, and all relevant literature published till November 30, 2019, were considered. Our analysis included 16 randomised controlled trials conducted with 4534 patients for exploring the effects of dexmedetomidine on POD in elderly patients following non-cardiac surgery. It was observed that the overall incidence of POD was significantly lower in the dexmedetomidine group than in the control group (risk ratio [RR] 0.51, 95% confidence interval [CI] 0.43-0.61, P < .01). Similar results were obtained from subgroup analysis upon comparison of the placebo (RR 0.52, 95% CI 0.41-0.66, P < .01, moderate quality of evidence), propofol-treated (RR 0.55, 95% CI 0.38-0.78, P < .01, low quality of evidence), and midazolam-treated (RR 0.38, 95% CI 0.20-0.71, P < .01, low quality of evidence) groups. Trial sequential analysis revealed that the cumulative z-value superseded the monitoring boundary and reached the required information size. However, patients who received dexmedetomidine had a higher incidence of bradycardia and hypotension. In conclusion, the meta-analysis revealed that dexmedetomidine appears to decrease the risk of POD in elderly patients following non-cardiac surgery. However, as some of the studies were heterogeneous and of low quality, high-quality trials are necessary for drawing more definitive conclusions.

[Analysis of mutations of 14 genes among 87 patients with myelodysplastic syndrome].

OBJECTIVE: To explore the correlation of genetic mutations and clinical features of myelodysplastic syndromes (MDS) with scores of Revised International Prognostic Scoring System (IPSS-R). METHODS: Eighty-seven patients with de novo MDS were enrolled. Mutations of MDS-related genes and clinical features were used to determine the incidence and subtype of mutations. Clinical features and IPSS-R scores of the patients with high frequency mutations involving TET2, TP53, ASXL1, RUNX1 and SF3B1 genes were compared. RESULTS: Fifty-four patients (62.1%) harbored at least one point mutation. The incidences of various mutations were significantly different, with the incidence of MDS-EB-2 being 100% and MDS-SLD being only 38.9%. Compared with the wild types, patients harboring mutations had higher lactate dehydrogenase, higher ß2 microglobulin, higher percentage of bone marrow blast cells and lower hemoglobin levels (P=0.027, <0.01, <0.01, 0.046, respectively). The IPSS-R scores of MDS patients with mutations were significantly higher than the wild types (P<0.01). The IPSS-R scores of the TP53 mutation groups were 7.82±1.83, which was significantly higher than the control group (3.77±1.66, P<0.01). No difference was found between the IPSS-R between patients carrying TET2, ASXL1, RUNX1, and SF3B1 mutations or the wild types (P>0.05). CONCLUSION: Genetic mutations are commonly found in MDS. MDS patients with mutations have unique clinical laboratory characteristics. Although the prognostic value of most genes is controversial, TP53 is an definite indicator of poor prognosis.

Uncoiling of helical boron nitride-graphene nanoribbons in a single-walled carbon nanotube.

Molecular dynamics simulation has been employed to study the encapsulation of boron nitride-graphene nanoribbons (BNCNRs) in a single-walled carbon nanotube (SWNT). The simulation results show that a helical BNCNR with large curvature can uncoil repeatedly and spontaneously in the SWNT, like the unwinding of the DNA in the nucleus. The uncoiling of the BNCNRs is accompanied by a system energy exchange between non-bonding energy and elastic potential energy due to the competition between the induction of graphene nanoribbon (GNR) segments and the resistance of boron nitride nanoribbon (BNNR) segments. The electronic transmission capacity of the BNCNR changes with the helical angle of the BNCNR, suggesting a changing electrical signal in the uncoiling and spiraling process. This study provides the opportunity to understand the encapsulation of the BNCNR in the SWNT in detail.

Liquid-Liquid Phase Transition in Nanoconfined Silicon Carbide.

We report theoretical evidence of a liquid-liquid phase transition (LLPT) in liquid silicon carbide under nanoslit confinement. The LLPT is characterized by layering transitions induced by confinement and pressure, accompanying the rapid change in density. During the layering transition, the proportional distribution of tetracoordinated and pentacoordinated structures exhibits remarkable change. The tricoordinated structures lead to the microphase separation between silicon (with the dominant tricoordinated, tetracoordinated, and pentacoordinated structures) and carbon (with the dominant tricoordinated structures) in the layer close to the walls. A strong layer separation between silicon atoms and carbon atoms is induced by strong wall-liquid forces. Importantly, the pressure confinement phase diagram with negative slopes for LLPT lines indicates that, under high pressure, the LLPT is mainly confinement-induced, but under low pressure, it becomes dominantly pressure-induced.

[Effects of intrathecal injection PI3K antagonist on inflammatory cytokines in spinal cord of bone cancer pain model in rats].

OBJECTIVE: To investigate the roles of PI3K in bone cancer pain, the present study was performed to demonstrate the changes of pain-related behavior and the production of IL-1ß, IL-6 and TNF-α after intrathecal injection of wortmannin (antagonist of PI3K receptors) in rat model. METHODS: A total of 44 SD rats were randomly divided into 4 groups, sham group (group S), sham + wormannin group (group SW), cancer group (group A), cancer + wortmannin group (group AW). Group S and group W were injected with 10 µl Hank's solution into left tibial medullary cavity; group A and group AW received injections of Walker 256 mammary cancer cells(10 µl, 2×10 cells/ml) into the same place to establish the model of bone cancer pain. In the meantime intratheacal catheterization was performed between L3 and L4 vertrbra on the rats of every group. Nine days after the operation, group S and group A received a single intratheacal injection of saline (0.9%, 10 µl), group SW and group AW received intratheacal wortmannin 0.5 µg/10 µl. Mechanical withdrawal thresholds were measured on the left hind paw before and every 10 min after intrathecal injection. Then the L4-L6 sections of spinal cord 30 min after injection were collected to determine the expression of IL-1ß, IL-6 and TNF-α. RESULTS: At 30 min post-injection, mechanical withdrawal thresholds of groups S, SW, A and AW were (30.1±4.3), (31.7±1.3), (17.2±2.0), (24.8±2.3) g respectively at Day 9 postinoculation (F=22.403, P<0.01), the mechanical withdrawal thresholds in group AW increased obviously versus group A. The expressions of TNF-α in groups S, SW, A and AW were (84.5±6.3), (78.7±12.5), (110.5±7.3), (57.8±4.6) pg/ml. Compared with groups S and W, the expression of TNF-α in group A showed a significant upregulation (F=28.119, P<0.01). CONCLUSIONS: An intrathecal injection of wortmannin may alleviate hyperalgesia, and inhibit the up-regulated expression of spinal cord inflammatory cytokines TNF-α in rats with bone cancer. PI3K may be involved in the development of bone cancer pain by regulating the expressions of TNF-α.

Theoretical study of the pathway to heterogeneous nucleation of liquid copper on the groove substrate with different wedge angles.

Heterogeneous nucleation is of significance in controlling the crystal growth, but the key route is still limited. Simulations are performed to explore the microscopic details of how the wedge substrate spreads its structural information to a growing crystal and further affects the solidification process. The simulation results show that, owing to the induced effect from the substrate, the copper atoms become layered at the liquid-solid interface in a "V"-shaped pattern and tend to form a twin crystal. The structural information delivery of the substrate decays with the distance away from the substrate, and the final solidified structure would gradually recover its inherent structure. Interestingly, the wedge angle of 90° seems to be an exception at which the solidified structure exhibits a perfect crystal due to the nearly perfect match with the Cu atoms. Moreover, the cooling rate and the atomic structure of the substrate are also found to have striking correlations with the final structures. These research results are favorable for a better understanding of the inherent relation between the solidified structure and the substrate.

[Combined inflating lung and insufflating calf pulmonary surfactant under general anesthesia in the treatment of postoperative intractable atelectasis].

OBJECTIVE: To explore the efficacy and safety of combined inflating lung and insufflating calf pulmonary surfactant under general anesthesia for treating postoperative intractable atelectasis. METHODS: From August 2006 to January 2013, 15 patients with obstinate postoperative atelectasis receiving pressure control lung expansion were enrolled. The bronchial cannula was intubated into the affected side to assist the expanding of the lung, and the calf pulmonary surfactant was insufflated selectively. The chest auscultation and computed tomography (CT) scan was performed at 1 d and 5 d after the procedure respectively, to evaluation the effect. The airway pressure, mean arterial pressure (MAP), heart rate (HR), respiratory rate (RR) and oxygen saturation (SpO2) were recorded before the treatment, during the treatment and after the treatment.Monitoring arterial blood gas before and after treatment. RESULTS: After the expansion of the lung and insufflation of calf pulmonary surfactants, the iconographic scan showed that collapsed alveolar was reinflated in 12 (80.0%) patients at 1 d after the treatment and in 14 patients(93.3%) at 5 d after the procedure.There were not notable vital sign change and complications during the treatment.At after the treatment, 1, 3, 5 and 7 d after the treatment, PaO2 was higher (P < 0.05), and there were not significantly difference in the PaCO2 and pH (P > 0.05) . CONCLUSION: Combined pressure control lung expansion with selectively insufflating calf pulmonary surfactant under general anesthesia may be an effective therapy for postoperative intractable atelectasis.