Nonlinear harmonic generation of terahertz waves in a topological valley polaritonic microcavity

Compact terahertz(THz)devices,especially for nonlinear THz components,have received more and more attention due to their potential applications in THz nonlinearity-based sensing,communications,and computing devices.However,effective means to enhance,control,and confine the nonlinear harmonics of THz waves remain a great challenge for micro-scale THz nonlinear devices.In this work,we have established a technique for nonlinear harmonic generation of THz waves based on phonon polariton-enhanced giant THz nonlinearity in a 2D-topologically protected valley photonic microcavity.Effective THz harmonic generation has been observed in both noncentrosymmetric and centrosymmetric nonlinear materials.These results can provide a valuable reference for the generation and control of THz high-harmonics,thus developing new nonlinear devices in the THz regime.

Insights into genetic variation and demographic history of sharpnose rays:examinations of three species of Telatrygon(Elasmobranchii,Dasyatidae)from the Indo-West Pacific

Coastal and demersal chondrichthyans(sharks,rays,and skates)are expected to exhibit high levels of genetic differentiation in areas of complex geomorphology.Population genetic studies investigating the extent to which demographic history shapes the genetic structure of thesefishes are rare.Here,we combined mitochondrial DNA(Cytb and ND2)and 8 nuclear microsatellite loci from 244 individuals to examine the population genetic structure and demographic history of the 3 Indo-West Pacific species of sharpnose rays(Telatrygon zugei,Telatrygon biasa,and Trygon crozieri).High levels of genetic variation both within and between species were identified.Phylogenetic analysis partitioned haplotypes into 2 lineages supporting divergence of T.zugei from T.crozieri and T.biasa during the Pleistocene.Furthermore,microsatellite-based clustering analyses identified 4 genetic groups(i.e.T.zugei from Japan,T.zugei from coastal China,T.biasa from Gulf of Thailand,and T.crozieri from the Andaman Sea).Measurements of genetic differentiation also support these 4 groups.Additionally,Pleistocene demographic expansions were examined in all genetic groups.The climate oscillations and current hydrologic cycles in the Indo-West Pacific appear to coincide with the hypothesis regarding speciation and the observed demographic history trends of the sharpnose rays.Considering the species group has,until recently,been thought to be one species,these results are critical for defining management units and guiding conservation efforts to preserve stingray biodiversity.