Sulfide (MoS2) spheres were fabricated by selective laser irradiation in liquid medium, which can be applied not only in preparation of colloidal spheres, but also in synthesis of micro- and submicromaterials. The phase and size of the resulted MoS2 spheres were found to be easily controlled by modulating input laser fluence. The influence of experimental parameters on colloidal spheres formation, including laser irradiation time, has been investigated systematically. Size-increasing and -reducing phenomenon can be observed by field-emission scanning emission microscope (FESEM), in which the average sizes of the obtained particles gradually increase with increasing laser irradiation time or fluence. Furthermore, the corresponding photocatalytic degradation rate of laser irradiated particles (61%) shows an obvious increasing when compares with the raw materials without laser processing (22%), which may provide a fast preparation way for the potential application in photocatalytic area.
The exciting properties of submicrometre sphere particles have been employed in many fields, such as the selective intervention characteristics and the size effect was widely used in the fields of biomedicine and sensing. However, the main synthesized methods at present were chemical or mechanical types, and several drawbacks existed. Recently, single pulsed laser irradiation in liquid has been confirmed as an innovative approach for fabrication of the submicrometre sphere particles due to the different optical absorption of precursor materials in a liquid phase, and many sphere particles for metal or alloy materials could be successfully synthesized. However, most of the semiconductor materials with low-optical absorption were disabled in this way, due to the laser energy under a proper wavelength was forbidden by the intrinsic wide bandgap of the semiconductor. Herein, based on the property of optical absorption, a double laser system was constructed to heat and assist fabrication by resonating wavelength matching. In the experiment section, the wide bandgap nanomaterials TiO2 was employed as the precursor and irradiated at the proper wavelength that originated from the optical absorption spectrum (532 nm for Nd: YAG laser and 324 nm for OPO laser, respectively). The results indicated that the submicrometre sphere particles could be well synthesized, and the morphology, optical absorption property was obtained improvement than that way of a single pulse.
Using 4×4 transfer matrix method, we investigated the transmission properties of defect mode in one-dimensional photonic crystal. The system can be transformed to be biaxial photonic crystal under one-way stress. It is found that the transmission properties of defect mode are critically depending on the numbers of dielectric layers and degree of asymmetry. For the system without stress, in the case of system with mirror symmetry, the defect mode is appearing gradually and its peak wavelength always keeps stable with the numbers of dielectric layers increasing, and its corresponding transmittance will be sharply decrease from a constant to zero at the same time. In the case of asymmetry, the defect mode is appearing gradually and its peak wavelength still keeps stable with the asymmetric degree continuously growth. Meanwhile, its transmittance exist an evolution from increase to decrease in this progress, and the maximum transmittance can be obtained at Δm=0 . After applying a fixed one-way stress on the system, the single defect mode will be split into Left-side defect mode (LDM) and Right-side defect mode (RDM). In the case of system with mirror symmetry, the two defect modes are appearing gradually and their peak wavelength always keep constant with the numbers of dielectric layers increasing, respectively, and their corresponding transmittance decrease asynchronously from a constant to zero. In the case of asymmetry, the peak wavelengths of LDM and RDM are being a constant with the changing of asymmetric degree and their corresponding transmittance are synchronously increasing or decreasing with the continuously increasing of asymmetric degree. Particularly, the maximum transmittance of defect mode also can be obtained at Δm=0 . This study provided a theoretical guidance for the best choice of numbers of dielectric layers to design a pressure sensor.
In this study, we focus on the analysis of one-dimensional photonic crystal with symmetric double defect. Using the transfer matrix method (TMM), the properties of defect modes including degeneracy and splitting, can be analyzed in detail. It is found that such properties are mainly depending on symmetry and spatial interval of defects. The results show that the degeneracy of defect modes occurs in two defects separate to each other. And defect modes split when two defects close to each other. The results have potential applications in photonic integration and fiber optic sensor.
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