A compact, low-noise, single-frequency fiber laser by using a newly developed ${\mathrm{Yb}}^{3+}$ heavily doped single-mode phosphate glass fiber has been demonstrated. Over $400\mathrm{mW}$ stable continuous wave single transverse and longitudinal mode laser at $1.06\mathrm{\mu m}$ was achieved from a $0.8\mathrm{cm}$ long active fiber. The measured slope efficiency and estimated quantum efficiency of laser emission are 72.7% and 93%, respectively. The signal-to-noise ratio is higher than $72\mathrm{dB}$, and the linewidth of the fiber laser is less than $7\mathrm{kHz}$, while the measured relative intensity noise is less than $-130\mathrm{dB}/\mathrm{Hz}$ at frequencies of over $1.5\mathrm{MHz}$.

Scintillators, which can convert high‐energy ionizing radiation into visible light, have been serving as the core component in radiation detectors for more than a century of history. To address the increasing application demands along with the concern on nuclear security, various strategies have been proposed to develop a next‐generation scintillator with a high performance in past decades, among which the novel approach via structure control has received great interest recently due to its high feasibility and efficiency. Herein, the concept of “structure engineering” is proposed for the exploration of this type of scintillators. Via internal or external structure design with size ranging from micro size to macro size, this promising strategy cannot only improve scintillator performance, typically radiation stopping power and light yield, but also extend its functionality for specific applications such as radiation imaging and therapy, opening up a new range of material candidates. The research and development of various types of structured scintillators are reviewed. The current state‐of‐the‐art progresses on structure design, fabrication techniques, and the corresponding applications are discussed. Furthermore, an outlook focusing on the current challenges and future development is proposed.

For first-order topological semimetals, non-Hermitian perturbations can drive the Weyl nodes into Weyl exceptional rings having multiple topological structures and no Hermitian counterparts. Recently, it was discovered that higher-order Weyl semimetals, as a novel class of higher-order topological phases, can uniquely exhibit coexisting surface and hinge Fermi arcs. However, non-Hermitian higher-order topological semimetals have not yet been explored. Here, we identify a new type of topological semimetal, i.e., a higher-order topological semimetal with Weyl exceptional rings. In such a semimetal, these rings are characterized by both a spectral winding number and a Chern number. Moreover, the higher-order Weyl-exceptional-ring semimetal supports both surface and hinge Fermi-arc states, which are bounded by the projection of the Weyl exceptional rings onto the surface and hinge, respectively. Noticeably, the dissipative terms can cause the coupling of two exceptional rings with opposite topological charges, so as to induce topological phase transitions. Our studies open new avenues for exploring novel higher-order topological semimetals in non-Hermitian systems.

We demonstrate a fundamentally mode-locked Yb-fiber laser with 3 GHz repetition rate and $\sim 206\mathrm{fs}$ pulse duration. The laser incorporates two enabling technologies: a 1 cm heavily Yb-doped phosphate glass fiber as the gain medium and a high-dispersion ($-1300{\mathrm{fs}}^2$) output coupler to manage cavity dispersion. The oscillator self-starts and generates up to 53 mW average power.

The purity of the synthesized orbital-angular-momentum (OAM) light in the fiber is inversely proportional to channel crosstalk level in the OAM optical fiber communication system. Here the relationship between the fiber structure and the purity is firstly demonstrated in theory. The graded-index optical fiber is proposed and designed for the OAM light propagation with the purity higher than 99.9%. 16 fiber modes (10 OAM modes) have been supported by a specific designed graded-index optical fiber with dispersion less than 35 ps/(km∙nm). Such fiber design has suppressed the intrinsic crosstalk to be lower than −30 dB, and can be potentially used for the long distance OAM optical communication system.