Two Ultraviolet Radiation Datasets that Cover China

Ultraviolet（UV） radiation has significant effects on ecosystems, environments, and human health, as well as atmospheric processes and climate change. Two ultraviolet radiation datasets are described in this paper. One contains hourly observations of UV radiation measured at 40 Chinese Ecosystem Research Network stations from 2005 to 2015. CUV3 broadband radiometers were used to observe the UV radiation, with an accuracy of 5%, which meets the World Meteorology Organization＇s measurement standards. The extremum method was used to control the quality of the measured datasets. The other dataset contains daily cumulative UV radiation estimates that were calculated using an all-sky estimation model combined with a hybrid model. The reconstructed daily UV radiation data span from 1961 to 2014. The mean absolute bias error and root-mean-square error are smaller than 30% at most stations, and most of the mean bias error values are negative, which indicates underestimation of the UV radiation intensity. These datasets can improve our basic knowledge of the spatial and temporal variations in UV radiation. Additionally, these datasets can be used in studies of potential ozone formation and atmospheric oxidation, as well as simulations of ecological processes.

Symmetry-protected third-order exceptional points in staggered flatband rhombic lattices

Higher-order exceptional points(EPs), which appear as multifold degeneracies in the spectra of non-Hermitian systems, are garnering extensive attention in various multidisciplinary fields. However, constructing higher-order EPs still remains a challenge due to the strict requirement of the system symmetries. Here we demonstrate that higher-order EPs can be judiciously fabricated in parity–time(PT)-symmetric staggered rhombic lattices by introducing not only on-site gain/loss but also non-Hermitian couplings. Zero-energy flatbands persist and symmetry-protected third-order EPs(EP3s) arise in these systems owing to the non-Hermitian chiral/sublattice symmetry, but distinct phase transitions and propagation dynamics occur. Specifically, the EP3 arises at the Brillouin zone(BZ) boundary in the presence of on-site gain/loss. The single-site excitations display an exponential power increase in the PT-broken phase. Meanwhile, a nearly flatband sustains when a small lattice perturbation is applied. For the lattices with non-Hermitian couplings, however, the EP3 appears at the BZ center. Quite remarkably, our analysis unveils a dynamical delocalization-localization transition for the excitation of the dispersive bands and a quartic power increase beyond the EP3. Our scheme provides a new platform toward the investigation of the higher-order EPs and can be further extended to the study of topological phase transitions or nonlinear processes associated with higher-order EPs.

Nontrivial coupling of light into a defect:the interplay of nonlinearity and topology

The flourishing of topological photonics in the last decade was achieved mainly due to developments in linear topological photonic structures.However,when nonlinearity is introduced,many intriguing questions arise.For example,are there universal fingerprints of the underlying topology when modes are coupled by nonlinearity,and what can happen to topological invariants during nonlinear propagation?To explore these questions,we experimentally demonstrate nonlinearity-induced coupling of light into topologically protected edge states using a photonic platform and develop a general theoretical framework for interpreting the mode-coupling dynamics in nonlinear topological systems.Performed on laser-written photonic Su-Schrieffer-Heeger lattices,our experiments show the nonlinear coupling of light into a nontrivial edge or interface defect channel that is otherwise not permissible due to topological protection.Our theory explains all the observations well.Furthermore,we introduce the concepts of inherited and emergent nonlinear topological phenomena as well as a protocol capable of revealing the interplay of nonlinearity and topology.These concepts are applicable to other nonlinear topological systems,both in higher dimensions and beyond our photonic platform.

Generation of all-fiber femtosecond vortex laser based on NPR mode-locking and mechanical LPG

An all-fiber femtosecond vortex laser based on common fiber components is constructed. It can produce femtosecond orbital angular momentum modes whose time pulse width is 398 fs. The topological charge of output orbital angular momentum （OAM） modes from this laser can be adjusted among 0, ＋1, and -1 easily while it is also easy to convert between continuous OAM modes and pulse OAM modes.

Synthetic optical vortex beams from the analogous trajectory change of an artificial satellite

We propose a method to generate specially shaped high-order singular beams of pre-designed intensity distributions. Such a method does not a priori assume a phase formula, but rather relies on the 'cake-cutting and assembly' approach to achieve the azimuthal phase gradient for beam shaping, inspired by the orbital motion trajectory change of an artificial satellite. Based on our method, several typical vortex beams with desired intensity patterns are experimentally generated. As an example, we realize optical trapping and transportation of microorganisms with a triangle-shaped vortex beam, demonstrating the applicability of such unconventional vortex beams in optical trapping and manipulation.