Nontrivial phase matching in helielectric polarization helices: Universal phase matching theory, validation, and electric switching.

Second-order optical nonlinearity is the essential concept for realizing modern technologies of optical wavelength conversion. The emerging helical polarization fluid, dubbed helielectric nematic, now makes it possible to design and easily fabricate various polarization structures and control their optical responses. The matter family is demonstrated as an ideal liquid platform for nonlinear optical conversion and amplification with electric-reconfigurable tunability. We here develop a universal phase matching theory and reveal a nonclassic chirality-sensitive phase-matching condition in the polarization helices through both the numerical calculation and the experimental validations. The nonlinear optical amplification can be dramatically modulated with a contrast ratio of >100:1 by an in-plane electric field. Furthermore, we employ the director relaxation under electric fields coupled with nonlinear optical simulation to clarify the topology-light interactions.

Response of helielectric nematics under an in-plane electric field.

In traditional chiral nematic liquid crystals, the apolar cholesterics, the dielectric effect is the main driving force for responding to an electric field. The emerging polar chiral nematics, dubbed helielectric nematics, are the polar counterparts of the cholesterics. The head-to-tail symmetry breaking of the new matter state enables it to respond sensitively to the polarity of an electric field. Here, we report on the observation of a sequential polar winding/unwinding process of polarization helices under an electric field applied perpendicular to the helical axes, which behaves distinctly from the unwinding of the apolar cholesteric helices. Understanding the helix-unwinding behaviors provides insights for developing switchable devices based on helielectric nematics.

Comparative Study of Flavonoid Profiles, Antioxidant, and Antiproliferative Activities in Hot-Air and Vacuum Drying of Different Parts of Pitaya (Hylocereus undatus Britt) Flowers.

Pitaya flower, a medicinal and edible plant commonly used in tropical and subtropical regions, was the focus of this study, which compared the effects of hot-air drying (HAD) and vacuum drying (VD) on phytochemical profiles and biological activities of its four parts: calyx, petals, stamens, and pistils. Both drying methods significantly increased the total phenolic content (TPC) of pitaya flowers, with values ranging from 1.86 to 3.24 times higher than those of fresh samples. Twelve flavonoid compounds were identified in pitaya flowers, with the glycoside derivatives of three flavonols (kaempferol, isorhamnetin, and quercetin) being the most abundant. VD resulted in 1.15 times higher total flavonoid glycoside content than HAD, whereas in petals, HAD yielded a total flavonoid glycoside content 1.21 times higher than VD. Both HAD and VD effectively increased the antioxidant capacities of pitaya flowers, though the difference between the two methods was not significant. Additionally, both drying methods enhanced the antiproliferative activity of pitaya flowers, with HAD showing a more significant effect than VD. The present study emphasized the efficacy of drying methods for enhancing flavonoids in pitaya flowers and provided insights for functional products' innovation with different parts of pitaya flowers.