We demonstrated a passively mode-locked fiber laser operating at 1982 nm by using a gold nanorods (GNRs) saturable absorber (SA). The GNRs SA was fabricated by mixing GNRs with sodium carbonxymethyl cellulose. By inserting the GNRs SA into a Tm-doped fiber laser cavity pumped by a 1570 nm fiber laser, stable passively mode-locking was achieved with a threshold pump power of 224 mW, ~4.02 ps pulses at 1982 nm with a repetition rate of ~37.49 MHz, and a maximum average power of ~6 mW was obtained for a pump power of ~265 mW.

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Recently, it was pointed out that all chiral crystals with spin-orbit coupling (SOC) can be Kramers Weyl semimetals (KWSs) which possess Weyl points pinned at time-reversal invariant momenta. In this work, we show that all achiral non-centrosymmetric materials with SOC can be a new class of topological materials, which we term Kramers nodal line metals (KNLMs). In KNLMs, there are doubly degenerate lines, which we call Kramers nodal lines (KNLs), connecting time-reversal invariant momenta. The KNLs create two types of Fermi surfaces, namely, the spindle torus type and the octdong type. Interestingly, all the electrons on octdong Fermi surfaces are described by two-dimensional massless Dirac Hamiltonians. These materials support quantized optical conductance in thin films. We further show that KNLMs can be regarded as parent states of KWSs. Therefore, we conclude that all non-centrosymmetric metals with SOC are topological, as they can be either KWSs or KNLMs.

In recent years, it had been shown that Berry curvature monopoles and dipoles play essential roles in the anomalous Hall effect and the nonlinear Hall effect respectively. In this work, we demonstrate that Berry curvature multipoles (the higher moments of Berry curvatures at the Fermi energy) can induce higher-order nonlinear anomalous Hall (NLAH) effect. Specifically, an ac Hall voltage perpendicular to the current direction emerges, where the frequency is an integer multiple of the frequency of the applied current. Importantly, by analyzing the symmetry properties of all the 3D and 2D magnetic point groups, we note that the quadrupole, hexapole and even higher-order Berry curvature moments can cause the leading-order frequency multiplication in certain materials. To provide concrete examples, we point out that the third-order NLAH voltage can be the leading-order Hall response in certain antiferromagnets due to Berry curvature quadrupoles, while the fourth-order NLAH can be the leading response in the surface states of topological insulators induced by Berry curvature hexapole. Our results are established by symmetry analysis, effective Hamiltonian and first-principles calculations. Other materials that support the NLAH effect are further proposed, including 2D antiferromagnets and ferromagnets, Weyl semimetals and twisted bilayer graphene near the quantum anomalous Hall phase.

Based on gold nanorods as saturable absorbers, diode-end-pumped passively Q-switched Nd:YAG lasers at 1064.3 and 1112 nm were demonstrated. In the 1064.3 nm laser, the maximum average output power was 101 mW. Pulses with 223 ns pulse width and pulse repetition rate of 300 kHz were achieved. In the 1112 nm laser, the maximum average output power of 236 mW was obtained. The shortest pulse width was 504 ns at a pulse repetition rate of 120 kHz.

Weyl semimetal (WSM), a novel state of quantum matter, hosts Weyl fermions as emergent quasiparticles resulting from the breaking of either inversion or time-reversal symmetry. Magnetic WSMs that arise from broken time-reversal symmetry provide an exceptional platform to understand the interplay between magnetic order and Weyl physics, but few WSMs have been realized. Here, we identify CeAlSi as a new non-centrosymmetric magnetic WSM via angle-resolved photoemission spectroscopy (ARPES) and first-principles, density-functional theory based calculations. Our surface-sensitive vacuum ultraviolet ARPES data confirms the presence of surface Fermi arcs as, the smoking gun evidence for the existence of the Weyl semimetallic state in CeAlSi. We also observe bulk Weyl cones in CeAlSi using bulk-sensitive soft-X-ray ARPES measurements. In addition, Ce 4f flat bands are found near the Fermi level, indicating that CeAlSi is a unique platform for investigating exotic quantum phenomena resulting from the interaction of topology, magnetism and electronic correlations.

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We report the generation of multiple soliton self-frequency shift cancellations in a temporally tailored tellurite photonic crystal fiber (PCF). The temporally regulated group velocity dispersion (GVD) is generated in the fiber by soliton induced optical Kerr effect. Two red-shifted dispersive waves spring up when two Raman solitons meet their own second zero-dispersion-wavelengths in the PCF. These results show how, through temporally tailored GVD, nonlinearities can be harnessed to generate unexpected effects.