Volume 14 Issue 9, September 2020

Launching electrons to the centre of an optical field with a vortex phase profile via extreme-ultraviolet photoionization makes coherent imprinting of the spatial distribution of the vortex beam onto the electron wave packet possible.

The photovoltaics market has long been dominated by silicon, but further improvements of these solar cells require novel approaches. Now, triplet–triplet annihilation photon upconversion has been used to harvest photons from below the bandgap of silicon, extending the spectral response and potentially improving the efficiency of these cells.

Directly relating the complex second-harmonic-generation field to the second-order susceptibility tensor allows tomographic imaging of nonlinear optical contrast at high frame rates.

Recent improvements of the operation speed of variable optical elements are reviewed with an emphasis on components with microsecond focus-varying response time.

Exploiting two-dimensional metamaterials, the direction of emission from InGaN/GaN quantum wells is engineered while simultaneously improving quantum efficiency.

Owing to the superlattice-induced bandgap and superlattice-enhanced density of states, small-twist-angled (<2°) bilayer graphene exhibits a strong gate-tunable photoresponse in the mid-infrared regime of 5 to 12 μm, reaching an extrinsic peak responsivity of 26 mA W⁻¹ at 12 μm.

The findings that the spatial distribution of an optical field with vortex phase profile can be imprinted coherently onto a propagating electron wave reveal new aspects of light–matter interactions and will help develop future single-photon electron spectroscopy.

Highly sensitive avalanche photodiodes that operate at near-infrared wavelengths of up to 2 μm could prove useful for eye-safe light imaging, detection and ranging, and other applications.

A tomographiac approach to second-harmonic-generation imaging on nonlinear structures is demonstrated, with experiments and three-dimensional reconstructions on a beta-barium borate crystal and various biological specimens performed.

Pt(ii) complexes allow the fabrication of efficient near-infrared organic light-emitting diodes that operate beyond the 900 nm region.

A strain-induced absorption-enhanced MoTe₂-based silicon photonic microring-integrated photodetector is demonstrated, featuring high responsivity of ~0.5 A W^–1 at 1,550 nm, with a low noise-equivalent power of 90 pW Hz^–0.5.

Photochemical upconversion of light with photon energy below the silicon bandgap has remained elusive, but the feat has now been demonstrated using PbS semiconductor nanocrystals and violanthrone.