Du Wang, Yaguo Li, Chuanchao Zhang, Wei Liao, Zeyu Li, Qinghua Zhang, and Qiao Xu
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| Fig. 1 (a) Experimental set-up of CO2 laser processing system. (b) Effective refractive index of SWS layer along the depth direction. For rectangular arrays the index step from the material to the air is from 1.35 to 1 and for hexagonal arrays the index step is from 1.16 to 1. (c) AR-SWSs of rectangular crater arrays. |
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-13-18351
Anti-reflection (AR) coating is a critical technology and an ongoing challenge for terahertz systems. The subwavelength structure (SWS) is an effective AR method, whereas the current manufacturing techniques, such as chemical etching and ultrafast laser processing, are low-efficient and low-quality for processing structures at the hundred-micron scale on hard brittle materials. We present a study of broadband SWSs directly ablated on the surface of quartz crystal by precisely controlled CO2 laser pulses, instead of commonly used ultra-fast lasers. The processing time of SWS can be shortened by two orders of magnitude compared with that by ultra-fast laser pulses. The SWS samples exhibit excellent AR properties with maximum transmittance of 97% at 0.71 THz, peak transmittance improvement of 13.5%, and optimal efficiency spectrum of 0.28–1.21 THz with transmittance >90%. The AR properties of SWS samples are in agreement with the simulated expectation and exist over a wide range of incidence angles up to ∼40°. The imaging of an object using SWS as the substrate shows an obvious improvement in imaging quality. We present an efficient and practical way to improve the transmission of optical components of materials, such as quartz crystal, alumina, and sapphire, in the terahertz band.
© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
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