Tunable Enhanced Second-Harmonic Generation in InP-InAsP Quantum Well Nanomembranes.

Second-harmonic generation (SHG) offers a convenient approach for infrared-to-visible light conversion in tunable nanoscale light sources and optical communication. Semiconductor nanostructures offer rich possibilities to tailor their nonlinear optical properties. In this study, strong second-harmonic generation in InP nanomembranes with InAsP quantum well (QW) is demonstrated. Compared with bulk InP, up to 100 times enhancement of SHG is achieved in the short-wave infrared range. This enhancement is shown to be predominantly induced by the resonance-enhanced absorption and quantum confinement of fundamental wavelengths in the InAsP QW. The thin nanomembrane structure will also provide nanocavity enhancement for second-harmonic wavelengths. The enhanced SHG peak wavelengths can also be tuned by changing the QW composition. These findings provide an effective strategy for enhancing and manipulating the second-harmonic generation in semiconductor quantum-confined nanostructures for on-chip all-optical applications.

Effects of haze pollution and institutional environment on demand for commercial health insurance.

What countermeasures should the public take as they become aware of the dangers of haze pollution? Insurance has the function of risk diversification, and little existing literature has focused on the relationship between haze pollution and commercial health insurance. This paper analyzes the impact of haze pollution on residents' demand for commercial health insurance and the heterogeneous impact of institutional environment using the 2017 China Household Finance Survey cross-sectional data (CHFS). The study finds that haze pollution raises residents' demand for commercial health insurance as their health risk perception level rises. The legal environment, market environment, and traditional culture affect the relationship between haze pollution and the demand for commercial health insurance. Further analysis reveals that the relationship between haze pollution and residents' demand for commercial health insurance can show significant regional heterogeneity, with a significant positive correlation in the eastern region and a significant negative correlation in the central and western regions. In addition, the preventive behaviors adopted by residents in the face of haze pollution can vary significantly depending on individual risk preferences. The findings of this paper are important for the public to take measures to cope with the haze pollution hazards. At the same time, insurance companies should improve their services to meet the needs of the public regarding haze pollution, which will contribute to the healthy development of the insurance industry.

Nonlinear microscopy of lead iodide nanosheets.

Lead iodide (PbI2) is a van der Waals layered semiconductor with a direct bandgap in its bulk form and a hexagonal layered crystalline structure. The recently developed PbI2 nanosheets have shown great promise for high-performance optoelectronic devices, including nanolasers and photodetectors. However, despite being widely used as a precursor for perovskite materials, the optical properties of PbI2 nanomaterials remain largely unexplored. Here, we determine the nonlinear optical properties of PbI2 nanosheets by utilising nonlinear microscopy as a non-invasive optical technique. We demonstrate the nonlinearity enhancement dependent on excitonic resonances, crystalline orientation, thickness, and influence of the substrate. Our results allow for estimating the second- and third-order nonlinear susceptibilities of the nanosheets, opening new opportunities for the use of PbI2 nanosheets as nonlinear and quantum light sources.

Green credit, environmental protection investment and debt financing for heavily polluting enterprises.

The paper takes listed companies in the heavily polluting industry from 2009-2017 as a research sample to explore whether heavy pollution enterprises' environmental protection investment helps their debt financing under the institutional background of China's continuous implementation of green credit policy. It is found that, in general, the environmental protection investment of heavy pollution enterprises helps them to obtain more and relatively long-term new loans; in terms of time, this effect is more evident after the release of China's Green Credit Guidelines in 2012; in addition, the level of regional environmental pollution, the level of financial development and the green fiscal policy also have a moderating effect on this. This paper enriches the study of the economic consequences of corporate environmental protection investment from the perspective of debt financing. It examines the effects of the implementation of China's green credit policy and other institutional factors to provide a reference for the heavy pollution enterprises' environmental protection investment and the implementation of green credit policy by local governments in China.

Tunable unidirectional nonlinear emission from transition-metal-dichalcogenide metasurfaces.

Nonlinear light sources are central to a myriad of applications, driving a quest for their miniaturisation down to the nanoscale. In this quest, nonlinear metasurfaces hold a great promise, as they enhance nonlinear effects through their resonant photonic environment and high refractive index, such as in high-index dielectric metasurfaces. However, despite the sub-diffractive operation of dielectric metasurfaces at the fundamental wave, this condition is not fulfilled for the nonlinearly generated harmonic waves, thereby all nonlinear metasurfaces to date emit multiple diffractive beams. Here, we demonstrate the enhanced single-beam second- and third-harmonic generation in a metasurface of crystalline transition-metal-dichalcogenide material, offering the highest refractive index. We show that the interplay between the resonances of the metasurface allows for tuning of the unidirectional second-harmonic radiation in forward or backward direction, not possible in any bulk nonlinear crystal. Our results open new opportunities for metasurface-based nonlinear light-sources, including nonlinear mirrors and entangled-photon generation.

High-Efficiency Visible Light Manipulation Using Dielectric Metasurfaces.

The development of a miniaturised device that provides efficient beam manipulation with high transmittance is extremely desirable for the broad range of applications including holography, metalens, and imaging. Recently, the potential of dielectric metasurfaces has been unleashed to efficiently manipulate the beam with full 2π-phase control by overlapping the electric and magnetic dipole resonances. However, in the visible range for available materials, it comes with the price of higher absorption that reduces efficiency. Here, we have considered dielectric amorphous silicon (a-Si) nanodisk and engineered them in such a way which provides minimal absorption loss in the visible range. We have experimentally demonstrated meta-deflector with high transmittance which operates in the visible wavelengths. The supercell of proposed meta-deflector consists of 15 amorphous silicon nanodisks numerically shows the transmission efficiency of 95% and deflection efficiency of 95% at operating wavelength of 715 nm. However, experimentally measured transmission and deflection efficiencies are 83% and 71%, respectively, having the experimental deflection angle of 8.40°. Nevertheless, by reducing the supercell length, the deflection angle can be controlled, and the value 15.50° was experimentally achieved using eight disks supercell. Our results suggest a new way to realise the highly transmittance metadevice with full 2π-phase control operating with the visible light which could be applicable in the imaging, metalens, holography, and display applications.