RESUMEN
Thermal imaging at the infrared wavelength regime has long been applied to different areas such as agriculture and defense industries. Metasurfaces, 2D engineered ultra-thin structures, have attracted much attention due to their compact size, superior performance, and different functionalities at optical frequencies. This work details the design and fabrication of high transmission metalenses operating at the long-wave infrared (LWIR) spectrum. We minimize the reflection losses through anti-reflection coating (ARC) while maintaining the full wavefront control at the central wavelength 9.07 µm. Our unit cell structure provides an average transmission of 97.5%. We experimentally verify our results and show that the fabricated metalenses perform diffraction-limited imaging at the design wavelength.
RESUMEN
OBJECTIVE: To compare the effectiveness of different mask types in limiting the dispersal of coughed air. METHOD: The Schlieren method with a single curved mirror was used in this study. Coughed air has a slightly higher temperature than ambient air, which generates a refractive index gradient. A curved mirror with a radius of curvature of 10 m and a diameter of 60 cm was used. The spread of the cough wavefront was investigated among five subjects wearing: (1) no mask; (2) a single surgical mask; (3) a double surgical mask; (4) a cloth mask; (5) a valveless N95 mask; and (6) a valved N95 mask. RESULTS: All mask types reduced the size of the contaminated region significantly. The percentage reduction in the cross-sectional area of the contaminated region for the same mask types on different subjects revealed by normalized data suggests that the fit of a mask plays an important role. CONCLUSIONS: No significant difference in the spread of coughed air was found between the use of a single surgical mask or a double surgical mask. Cloth masks may be effective, depending on the quality of the cloth. Valved N95 masks exclusively protect the user. The fit of a mask is an important factor to minimize the contaminated region.