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In this work, conical cavities with a fixed top diameter and varied bottom diameter have been utilized to improve the signal intensity, signal-to-noise ratio (SNR), and signal stability of laser-induced breakdown spectroscopy (LIBS). It is observed that the postponement of the maximum enhancement of spectral intensity and SNR occurs abnormally with decreasing the bottom diameter due to the energy dissipation from the plasma to the cavity walls. Optimization of the cavity size indicates that the conical cavity is superior to the widely-used cylindrical cavity in improving the performance of LIBS. It is also found that the emission enhancement in the conical cavity with larger bottom diameters is attributed to the increase in plasma temperature and electron number density, but the enhancement in the conical cavity with smaller bottom diameters is ascribed to the growth of electron number density. For the first time, the exact efficiencies of conical cavities suppressing the total number density fluctuation are acquired to evaluate the performance of improving signal stability through analysis of the signal uncertainty composition. [ABSTRACT FROM AUTHOR]

Carbon materials have become a research hotspot in many fields because of their unique properties. In this paper, carbon nanowires (CNWs) were constructed with the finite-difference time-domain (FDTD) technique, and the effects of different structural parameters on the optical absorption properties of CNWS arrays at 350–810 nm were investigated. The results show that different lengths, diameters and spacings of the nanowires lead to different absorption properties of the arrays. In addition to a sharp decrease in the absorption at high incidence or viewing angles, the arrays have strong absorption properties at other angles. However, the array absorption at high incidence or viewing angles can be enhanced to some extent by varying the lengths of the nanowires. The wavelength and polarization direction of the excitation light have little effect on the absorption properties of the arrays. It is very important to determine the corresponding structural parameters of CNWs with the strongest absorption for the fabrication of nanowire arrays and their applications in stealth technologies, nanolight-emitting devices, photoelectric sensors and photovoltaic cells. [ABSTRACT FROM AUTHOR]