Nature Photonics最新文献

Vortex phenomena are ubiquitous in nature. In optics, despite the availability of numerous techniques for vortex generation and detection, topological protection of vortex transport with desired orbital angular momentum (OAM) remains a challenge. Here, by use of topological disclination, we demonstrate a scheme to confine and guide vortices featuring arbitrary high-order charges. Such a scheme relies on twofold topological protection: a non-trivial winding in momentum space due to chiral symmetry, and a non-trivial winding in real space due to the complex coupling of OAM modes across the disclination structure. We unveil a vorticity-coordinated rotational symmetry, which sets up a universal relation between the vortex topological charge and the rotational symmetry order of the system. As an example, we construct photonic disclination lattices with a single core but different C_n symmetries and achieve robust transport of an optical vortex with preserved OAM solely corresponding to one selected zero-energy vortex mode at the mid-gap. Furthermore, we show that such topological structures can be used for vortex filtering to extract a chosen OAM mode from mixed excitations. Our results illustrate the fundamental interplay of vorticity, disclination and higher-order topology, which may open a new pathway for the development of OAM-based photonic devices such as vortex guides, fibres and lasers.

The realization of photonic time crystals is a major opportunity but also comes with considerable challenges. The most pressing one, potentially, is the requirement for a substantial modulation strength in the material properties to create a noticeable momentum bandgap. Reaching that noticeable bandgap in optics is highly demanding with current, and possibly also future materials platforms because their modulation strength is small by tendency. Here we demonstrate that by introducing temporal variations in a resonant material, the momentum bandgap can be drastically expanded with modulation strengths in reach with known low-loss materials and realistic laser pump powers. The resonance can emerge from an intrinsic material resonance or a suitably spatially structured material supporting a structural resonance. Our concept is validated for resonant bulk media and optical metasurfaces and paves the way towards the first experimental realizations of photonic time crystals.

Attosecond transient absorption resolves the instantaneous response of a quantum system as it interacts with a laser field, by mapping its sub-cycle dynamics onto the absorption spectrum of attosecond pulses. However, the quantum dynamics are imprinted in the amplitude, phase and polarization state of the attosecond pulses. Here we introduce attosecond transient interferometry and measure the transient phase, as we follow its evolution within the optical cycle. We demonstrate how such phase information enables us to decouple the multiple quantum paths induced in a light-driven system, isolating their coherent contribution and retrieving their temporal evolution. Applying attosecond transient interferometry reveals the Stark shift dynamics in helium and retrieves long-term electronic coherences in neon. Finally, we present a vectorial generalization of our scheme, theoretically demonstrating the ability to isolate the underlying anomalous current in light-driven topological materials. Our scheme provides a direct insight into the interplay of light-induced dynamics and topology. Attosecond transient interferometry holds the potential to considerably extend the scope of attosecond metrology, revealing the underlying coherences in light-driven complex systems.