Parametric Nonlinear Optics with Layered Materials and Related Heterostructures

Nonlinear optics is of crucial importance in several fields of science and technology with applications in frequency conversion, entangled‐photon generation, self‐referencing of frequency combs, crystal characterization, sensing, and ultra‐short light pulse generation and characterization. In recent years, layered materials and related heterostructures have attracted huge attention in this field, due to their huge nonlinear optical susceptibilities, their ease of integration on photonic platforms, and their 2D nature which relaxes the phase‐matching constraints and thus offers a practically unlimited bandwidth for parametric nonlinear processes. In this review the most recent advances in this field, highlighting their importance and impact both for fundamental and technological aspects, are reported and explained, and an outlook on future research directions for nonlinear optics with atomically thin materials is provided

Optical Graphene Gas Sensors Based on Microfibers: A Review

Graphene has become a bridge across optoelectronics, mechanics, and bio-chemical sensing due to its unique photoelectric characteristics. Moreover, benefiting from its two-dimensional nature, this atomically thick film with full flexibility has been widely incorporated with optical waveguides such as fibers, realizing novel photonic devices including polarizers, lasers, and sensors. Among the graphene-based optical devices, sensor is one of the most important branch, especially for gas sensing, as rapid progress has been made in both sensing structures and devices in recent years. This article presents a comprehensive and systematic overview of graphene-based microfiber gas sensors regarding many aspects including sensing principles, properties, fabrication, interrogating and implementations

Analysis of factors influencing vibration reduction and design optimization of damping holes in adjacent tunnel blasting

Drilling and blasting is still the most widely used method for tunnel excavation in hard rocks. However, this method causes damage to adjacent buildings and structures mainly because of tunnel blast-induced vibrations. Currently, no specific guidelines are available for optimizing the design of damping holes during controlled blasting. Therefore, this study analyzes the vibration reduction mechanism of damping holes. Six key factors, namely, hole radius, hole spacing, coverage length, arrangement type, number of rows, and row spacing, that can affect the blasting vibration reduction were analyzed theoretically. Six groups of 30 numerical models were established using LS-DYNA. The influences of the six factors on the average and maximum velocities and stress vibration reduction were analyzed to quantitatively evaluate their damping effects. Then, optimization design suggestions for damping holes were proposed. The results revealed that it is necessary to increase the hole diameter and reduce the hole and row spacings as much as possible. The reasonable coverage length of damping holes is 1.5 times the coverage length of blasting holes. The blossom-type arrangement is recommended for practical engineering applications and the number of rows of damping holes should not exceed four. Guidelines for reducing vibration in adjacent tunnel blasting were formulated. Finally, the optimized damping hole design was applied to a typical tunnel project, which verified its reasonability and applicability

Dynamic and Active THz Graphene Metamaterial Devices

In recent years, terahertz waves have attracted significant attention for their promising applications. Due to a broadband optical response, an ultra-fast relaxation time, a high nonlinear coefficient of graphene, and the flexible and controllable physical characteristics of its meta-structure, graphene metamaterial has been widely explored in interdisciplinary frontier research, especially in the technologically important terahertz (THz) frequency range. Here, graphene’s linear and nonlinear properties and typical applications of graphene metamaterial are reviewed. Specifically, the discussion focuses on applications in optically and electrically actuated terahertz amplitude, phase, and harmonic generation. The review concludes with a brief examination of potential prospects and trends in graphene metamaterial

Numerical and experimental study of laser aided additive manufacturing for melt-pool profile and grain orientation analysis

Laser aided additive manufacturing (LAAM), a blown powder additive manufacturing process, can be widely adopted for surface modification, repair and 3D printing. A robust numerical model was developed to simulate convective fluid flow and balancing of surface tension forces at the air-fluid interface to predict melt-pool free surface curvature and solidified clad dimensions. The free surface physical interface was calculated using the Arbitrary Lagrangian Eulerian (ALE) moving mesh approach. Powder deposition efficiency was considered by activating mesh normal velocity at melted regions based on localized powder mass flux intensity from the discrete coaxial powder nozzles. The heat flux equation used for representing the laser heat source considered attenuation effect from the interaction between the powder jets and laser as well as heat sink effects of un-melted powder particles entering the melt-pool. The predicted thermal gradient directions agree well with grain growth orientations obtained from electron backscatter diffraction (ESBD) analysis in three different cross-sectional orientations. Experimental validation of clad width, height and melt-pool depth shows a maximum error of 10% for a wide range of processing parameters which consider the effects of varying laser power, laser scanning speed and powder feeding rate.ASTAR (Agency for Sci., Tech. and Research, S’pore