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The observation of terahertz nonlinearities in graphene and quantum wells and the emission of terahertz waves from water show that terahertz science is still a fertile area of research that is full of surprises.
Reflected light is often unwanted, causing interference, and reducing transmitted power. Controlling the non-local response of a material can lead to anti-reflection coatings with impressive properties.
With the availability of high-intensity terahertz free-electron lasers, surprisingly large multiphoton absorptions in a phosphorus atom doped in a silicon crystal have been obtained, providing the possibility of a hydrogen-like system in silicon photonics and quantum information devices.
Phosphors often suffer luminescence quenching at elevated temperatures. Now, thermal quenching can be combated with surface phonon-assisted energy transfer, enabling the luminescence of ultrasmall upconversion nanophosphors to be dramatically enhanced.
Irradiating arrays of metal nanowires with intense femtosecond laser pulses produces high-brightness picosecond X-ray pulses. By specifically tailoring the plasma properties, up to 20% conversion efficiency of optical light into X-rays can be achieved.
Implementing non-reciprocal elements with a bandwidth comparable to optical frequencies is a challenge in integrated photonics. Now, a phonon pump has been used to achieve optical non-reciprocity over a large bandwidth.
The study of the complex, unstable dynamics of lasers is not just of scientific value but is also creating new opportunities for making secure lidar and generating high-frequency microwave signals.
The ability to switch fluorophores on and off is key to performing super-resolution nanoscopy. To date, all switching schemes have been based on an incoherent response to the laser field. Now, a nanoscope that uses on–off coherent switching of quantum dots has been demonstrated.
Metasurfaces can in principle provide a versatile platform for optical functionalities, but in practice designing and fabricating them to specifications can be difficult. Now, the realization of metasurfaces with engineered disorder allows for versatile optical components that combine the best features of periodic and random systems.
