Generation of a vortex point adjustable vortex array based on decentered annular beam pumping.

An adjustable optical vortex array (OVA) based on decentered annular beam pumping has been demonstrated in an end-pumped Nd:YVO4 laser. This method allows for not only the transverse mode locking of different modes, but also the ability to adjust the mode weight and phase by manipulating the position of the focusing lens and axicon lens. To explain this phenomenon, we propose a threshold model for each mode. Using this approach, we were able to generate optical vortex arrays with 2-7 phase singularities, achieving a maximum conversion efficiency of 25.8%. Our work represents an innovative advancement in the development of solid-state lasers capable of generating adjustable vortex points.

Transverse mode locking of different frequency-degenerate families based on annular beam pumping.

Optical vortex arrays have been achieved in an end-pumped Nd:YVO4 laser pumped by an annular beam. Spontaneous transverse mode locking of Laguerre-Gaussian modes in different frequency-degenerate families has been obtained by merely adjusting the pump power. A maximum output power of 0.88 W and optical conversion efficiency of 13.6% are achieved for optical vortex arrays. Optical vortex arrays formed in different frequency-degenerate families of Laguerre-Gaussian modes can be actively controlled by the position of the axicon. This work provides a way to research transverse mode locking of Laguerre-Gaussian modes in different frequency-degenerate families based on annular beam pumping.

Design and optical characterization of an efficient polarized organic light emitting diode based on refractive index modulation in the emitting layer.

Luminescent liquid Crystal (LC) material is regarded as the most promising material for polarized organic light emission due to their intrinsic characteristics including orderly alignment and luminescence. Nevertheless, the optical extraction efficiency of LC based organic light emitting diodes (OLEDs) devices still requires significant effort and innovation towards real-world applications. In this paper, we propose the design of a highly linearly polarized light-emission from OLEDs with integrated refractive index nanograting in the emissive layer (EML) based on photo aligned luminescent liquid crystal material. The simulation results indicate that the geometrically optimized polarized device yields an external quantum efficiency (EQE) up to 47% with a polarized ratio up to 28 dB at a 550 nm emission wavelength. This conceptual design offers a new opportunity to achieve efficient polarized organic luminescence, and it is (to the best of our knowledge) the first approach that enhances the light extraction of OLEDs based on luminescent liquid crystal via index grating in the EML.

Endovascular and open surgical repair of abdominal aortic aneurysms: A comparative analysis of western and Chinese studies.

Abdominal aortic aneurysms (AAA) are life-threatening serious conditions that require effective and quick management. Although it is generally acknowledged that patients with AAA obtain the greatest benefit from endovascular repair (EVAR) compared to open surgical repair (OSR), there are few comparisons between the surgical approaches in Western versus Chinese patients. We aimed to perform a meta-analysis of studies in which EVAR was compared with OSR in the management of abdominal aortic aneurysms. We searched the Western literature through PubMed, OVID and Web of Science from 1991 until December 2018 and the Chinese-language literature from 1998 until December 2018. We pooled the results in January 2019 based on standardized inclusion and exclusion criteria and analyzed them using a conventional meta-analysis. Forty-five English papers with 31,074 AAA patients and twenty-one Chinese studies with 1,405 patients were included in this study. Chinese subjects were more likely to undergo endovascular repair than Western subjects (44.5% versus 41.5%, P = 0.012). The 30-day post-discharge mortality rate in Western studies was significantly lower for EVAR than for OSR (odds ratio (OR) = 0.481, P < 0.001). However, there was no significant reduction in the 30-day mortality rate following EVAR compared to OSR (OR = 0.733, P = 0.425) for Chinese patients. In Western patients, the postoperative complication rate of respiratory system and cardiac system was lower in the EVAR group than in the OSR group (OR = 0.270, P < 0.001 and OR = 0.411, P < 0.001, respectively), nevertheless, for Chinese patients, limb ischaemia was more common (OR = 1.539, P = 0.049) in the EVAR group. Whether in Western patients with an eight-year follow-up period or Chinese patients with a maximum four-year follow-up period, there was no significant difference between the EVAR and OSR groups in the all-cause death rate (hazard ratio (HR) = 1.026, P = 0.483 and HR = 1.173, P = 0.247, respectively). Chinese patients were more likely to receive EVAR than OSR and the 30-day mortality was significantly lower for EVAR than for OSR in Western patients but not in Chinese patients. Endovascular repair can be applied to Chinese patients with a reasonable safety margin. Further work is needed to explore the causes of these treatment differences.

Investigation of a highly compact intracavity actively Q-switched cascade diamond Raman laser.

A laser diode (LD) pumped intracavity chemical vapor deposition (CVD) diamond cascade Raman laser is reported here. By rotating a Brewster plate (BP) in the laser resonator, the Raman laser with tunable output coupling rate is achieved. The highly compact diamond laser emitted 1240 nm and 1485 nm Stokes light simultaneously via optimization of the pumping direction. The slope efficiency of the intracavity diamond laser is improved by optimizing the output coupling rate and adjusting the repetition rate of the 1064 nm fundamental laser. Ultimately, the maximum slope efficiency of the first Stokes light (1240 nm) is 16.8%, and the corresponding output power is about 0.6 W. The maximum peak power is 2.5 kW when the power of 808 nm LD is 34.7 W.

DNDMH-mediated direct nitration of aryl alkenes.

N-nitro type reagents have been demonstrated as mild nitration tools in recent years. This work presents an exploration of direct nitration of aryl alkenes mediated by DNDMH, a novel N-nitro type reagent developed in our previous study. It exhibits herein a new property of DNDMH as an effective direct nitration reagent for aryl alkenes, through probably the delivery of nitro radicals with the aid of TEMPO and Cu(OAc)2.

Dinitro-5,5-Dimethylhydantoin: An Arene Nitration Reagent.

The development of a new N-nitro type compound, dinitro-5,5-dimethylhydantoin (DNDMH), has been reported as an arene nitration reagent. The exploration demonstrated that arene nitration with DNDMH exhibited good tolerance with diverse functional groups. It is notable that, among the two N-nitro units of DNDMH, only the N-nitro unit on N1 was delivered to the nitroarene products. The N-nitro type compound with a single N-nitro unit on N2 cannot promote the arene nitration.

Solving the overlapped absorbance profile in gas detection by Lorentz distribution solution based on direct absorption spectroscopy method.

A novel method of Lorentz distribution solution (LDS) from overlapped absorbance profile in time domain (incomplete absorbance profile in frequency domain) based on the direct absorption spectroscopy method (DAS) was experimentally demonstrated. It utilized the ratio of the integral in a certain interval on the lower horizontal axis of the Lorentzian profile to the integral in the entire interval on the horizontal axis has a certain relationship and can be expressed by a formula. This method effectively solves the difficulties of extracting gas concentration from incomplete absorbance profile. Formulation and detection procedure were presented, experiments were carried out to prove the method on the extraction of gas concentration from different overlapped absorbance profile and different concentration. Compared with the conventional DAS (C-DAS), the maximum relative errors on the concentration extraction are minimized from 25.55% to 2.64% at different concentration and absorbance profile. Meanwhile, the experimental results show that the obtained gas concentration by LDS presents a good linear relationship while those measured by C-DAS are significantly different.

High-power high-repetition-rate UV light at 355 nm generated by a diode-end-pumped passively Q-switched Nd:YAG laser.

We describe experimental results with a diode-pumped, passively Q-switched extracavity second- and third-harmonic generation. Cr:YAG is used as a saturable absorber for pulse generation. Taking into account the thermal effects of Nd:YAG at high incident pump power, we use a short plane-to-plane cavity configuration to take advantage of the maximum pump power and obtain the compactness structure. At the same time, we use the type-I critical phase-matched lithium triborate crystal to generate light at 532 nm and mix the residual fundamental at 1064 nm and the second-harmonic wave at 532 nm in the type-II critical phase-matched lithium triborate crystal for UV light generation at 355 nm. A third-harmonic-generation output power of 1.32 W is achieved at the incident pump power of 27.5 W, corresponding to an optical-to-optical efficiency of 4.8%. The instability of the UV laser power is less than 5% for 4 h.