RESUMO
Polarization modulation of electromagnetic waves plays an important role in the field of optics and optoelectronics. Current polarization optics are typically limited to the modulation in a single transverse plane. However, manipulating polarization along the longitudinal direction is also important for full-space polarization modulation. Here, we propose two kinds of all-dielectric terahertz metasurfaces for longitudinally spatial polarization manipulation. The metasurfaces are capable of controlling polarization along the propagation path, namely: i) a longitudinal bifocal metalens with different polarization states at each focal point, and ii) a versatile metalens can simultaneously generate a uniformly polarized focused beam and a vector beam with varying polarization along the propagation path. Furthermore, the measurement of the dielectric thickness is demonstrated based on the polarization modulation feature of the metalens. The proposed metasurfaces allow for effective polarization state alteration along the propagation path, exhibiting significant potential for applications in versatile light-matter interactions, optical communications, and quantum optics.
RESUMO
BACKGROUND: Seasonal late-season water deficits negatively affect the yield and quality of sweet potatoes in northern China. However, the amount of late-season irrigation to achieve high yield and consistent quality storage root remains undetermined. We assessed the yield and some qualitative traits of sweet potatoes such as size, shape, skin/flesh colour and nutritional content, as influenced by five irrigation levels (T0: unirrigated control; T1: 33% ETc; T2: 75% ETc; T3: 100% ETc; and T4: 125% ETc). RESULTS: Late-season irrigation significantly increased yield and marketable yield. Yields for T2 and T3 were significantly higher than other treatments, whereas T2 had the highest Grade A rating in a 2-year test. The vertical length of storage roots gradually increased with an increase in irrigation level, whereas the maximum width remained unchanged. The proportion of long elliptic and elliptic storage roots also increased, whereas the proportion of ovate, obovate and round storage roots gradually decreased. The skin and flesh colours became more vivid as the level of irrigation increased, with the skin colour becoming redder and the flesh colour becoming more orange-yellow. The levels of carotenoids, vitamin C and soluble sugar were significantly higher in irrigated crops, with the highest vitamin C and soluble sugar levels in T2 and the highest carotenoid levels in T3 treatment. CONCLUSION: Taken together, these results demonstrate the potential of moderate irrigation in the late-season to improve both yield production and quality potential. The results are of great importance for improving the market value of sweet potatoes and increasing grower profits. © 2024 Society of Chemical Industry.
