By using infrared to ultraviolet (IR-UV) femtosecond laser directing, periodic nanostructures were efficiently fabricated on an F-doped tin oxide (FTO) film with a thickness of 650 nm. The morphology of the nanostructures and duty cycle were studied in detail by changing the laser fluence and scanning speed, where three lasers with central wavelengths of 343, 515, and 1,030 nm were used in the experiments. Under the 515 nm laser irradiation with scanning speed of 0.01 mm/s and laser fluence of 23 mJ/cm2, the periods Λ is 172 nm, the ablated nanogroove with width w2 is 52 nm, the birefringence Δn reached a maximum of 0.21, and the phase retardance was up to 135 nm. The morphology of the nanostructures and the birefringence effects of the FTO film prepared by a femtosecond laser at wavelengths of 1,030 and 343 nm were also studied, where the phase retardance of the nanostructured FTO film was much lesser than for the 515 nm laser because the thickness of the nanoripples layer, and, thus, the duty cycle of periodic nanoripples was smaller. Finally, a large-area FTO film with periodic nanostructures was fabricated efficiently by direct laser writing using a 515 nm fs laser beam focused via a cylindrical lens, and demonstrated the characteristics of a quarter-wave plate for 532 nm light.
Accurate location information is indispensable for the emerging applications of Internet of Vehicles (IoV), such as automatic driving and formation control. In the real scenario, vision-based localization has demonstrated superior performance to other localization methods for its stability and flexibility. In this paper, a scheme of cooperative vision-based localization with communication constraints is proposed. Vehicles collect images of the environment and distance measurements between each other. Then vehicles transmit the coordinates of feature points and distances with constrained bits to the edge to estimate their positions. The Fisher information matrix (FIM) for absolute localization is first obtained, based on which we derive the relative squared position error bound (SPEB) through subspace projection. Furthermore, we formulate the corresponding bit allocation problem for relative localization. Finally, a variancebased gradient descent (V-GD) algorithm is developed by considering the influence of photographing, distance measurements and quantization noises. Compared with conventional bit allocation methods, numerical results demonstrate the localization performance gain of our proposed algorithm with higher computational efficiency.
Ultrafast laser-induced periodic surface structures (LIPSSs) have been studied intensely in the last two decades, which have become a useful method for surface nanostructures and are widely used to tune surface properties. This paper reported the fabrication of high-spatial-frequency LIPSSs (HSFLs) on FTO film induced by 1,030[Formula: see text]nm femtosecond laser. The morphology, duty cycle and birefringence effects of HSFLs were studied in detail by changing the laser fluence and scanning speed. Clear and uniform HSFLs were formed over the entire ablated area when the laser fluence and scanning speed were 89[Formula: see text]mJ/cm2 and 0.01[Formula: see text]mm/s, respectively. The duty cycle of the HSFL was measured to be as high as 0.36, and the thickness of the HSFL layer was found to be in the range of 409–546[Formula: see text]nm. The phase retardation of the FTO film with HSFLs could reach up to 96[Formula: see text]nm and could be used as an optical attenuator with a tunable range of 71–100% for 532[Formula: see text]nm linear polarized light.
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