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In recent years, the metallization of polymers has been intensely studied as it takes advantage of both plastics and metals. Laser direct writing (LDW) is one of the most widely used technologies to obtain metal patterns on polymer substrates. In LDW technology, different methods including injection-molding, drop-casting, dip coating, and spin coating are utilized for surface preparation of polymer materials prior to the laser activation process. In this study, an atomization based dual regime spray coating system is introduced as a novel method to prepare the surface of the materials for LDW of metal patterns. Copper micropatterns on the polymer surface were achieved with a minimum feature size of 30 μm, having a strong adhesion and excellent conductivity. The results show that the dual regime spray deposition system can be potentially used to obtain uniform thin film coating with relatively less material consumption on the substrates for surface preparation of laser direct metallization of polymers.

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In this research, we proposed fabrication process of optical fiber sensors using femtosecond laser and their applications. A beam of femtosecond laser was focused by an objective lens in the optical fiber. By testing different conditions, a group of machining parameters was found that achieve a minimum machining resolution of 3.2 μm. To ablate the core of the optical fiber, which is buried deep inside the cladding, precisely, part of the cladding was removed to expose the core as close as possible to the air. By making a complex pattern to modify the optical path of the laser inside an optical fiber, a sensitivity of 942.8–1015.6 nm per refractive index unit (nm/RIU) was obtained for liquid refractive index sensing. For another sensor, a sensitivity of 1.38 × 105 nm/RIU was obtained, which is high enough to detect small amount of refractive index change of air. It is known to be the first time that we fabricated a complex microstructure in an optical fiber to modify the propagation of the light using femtosecond laser. This research shows the possibility of a complex modification of light in an optical fiber using laser machining.

In this research, we proposed fabrication process of optical fiber sensors using femtosecond laser and their applications. A beam of femtosecond laser was focused by an objective lens on the optical fiber. By testing different conditions, a group of machining parameters was found that achieve a minimum machining resolution of 3.2 μm. To ablate the core of the optical fiber, which is buried deep inside the cladding, precisely, part of the cladding was removed to expose the core as close as possible to the air. By making a complex pattern to modify the optical path of the laser inside an optical fiber, a sensitivity of 942.8 to 1015.6 nm/RIU was obtained for liquid refractive index sensing. For another sensor, a sensitivity of 1.38 × 105 nm/RIU was obtained which is high enough to detect small amount of refractive index change of air. It is known to be the first time that we fabricated a complex microstructure in an optical fiber to modify the propagation of the light using femtosecond laser. This research shows the possibility of a complex modification of light in an optical fiber using laser machining.

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