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We demonstrate a structure for a vertical-cavity surface-emitting laser (VCSEL) with a mode filter and half-wavelength (λ/2) cavity. The effects of λ/2- and λ-cavities on the threshold current are studied. The thickness and etched diameter of the mode filter are optimised to achieve single-transverse-mode output. The results show that when changing from λ-cavity to λ/2-cavity, the threshold current of the VCSEL decreases by 30.7% (from 0.85 mA to 0.65 mA). In addition, for the mode-filter thickness of 80 nm, and the etched diameter of 2.5 μm, the side mode suppression ratio reaches 90 dB, which meets the requirement of single-transverse-mode output. The VCSELs with the optimised design can overcome many difficulties and have great potential in 3D face recognition.

GGG70L is a kind of cold-working die steel widely used in large automobile cover parts die. In order to ensure the life of the die, laser quenching process is usually used to form a certain hardened layer at a specific part of the die. In this paper, the changes of microstructure and hardness of ductile iron GGG70L after laser quenching were studied through a large number of process experiments, and the influence of quenching process parameters on the microstructure and properties of GGG70L was obtained. The relationship between the depth of hardened layer and the laser energy density is established and a quadratic function relationship was found between the two. It is found that both higher hardness and deeper hardening depth can be obtained when the energy density is 24-28 (J/mm2). The finite element model of the laser quenching process of GGG70L was established, and the temperature of the hardened zone and its evolution law during the laser quenching process were studied numerically.

Friction stir processing (FSP) is a method to produce severe plastic deformation (SPD) of materials, which can well improve and optimize the microstructure and mechanical properties of Mg-Li alloy. In this paper, the FSP experiment of LA103Z Mg-Li alloy was conducted, and the influence of process parameters on the microstructure, tensile strength, elongation after fracture and fracture morphology of the material was studied. The microstructure of the Mg-Li alloy after FSP was significantly refined. With the increasing rotational speed of the stirring head, the grain boundaries became clearer and more distinguishable, and the low angle grain boundaries transformed into the high angle grain boundaries. With the increasing feed speed of the stirring head, the grain refinement became more pronounced, and the dispersion of α-Mg phase in the stir zone became more uniform and distributed at the grain boundaries. When the rotational speed and the feed speed of the stirring head were 800-1000 r/min and 100-200 mm/min respectively, the comprehensive performance of the Mg-Li alloy plate after FSP was expected to be optimal.

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