Volume 13 Issue 1, January 2019

Focusing short CO₂ laser pulses into air reveals rich ionization physics that is best explained by solid-state theories and results in centimetre-scale-diameter megafilaments that transport joules of energy.

An on-chip Brillouin laser with a sub-hertz linewidth opens the door for applications in data communication, metrology and sensing.

Rather than requiring millions of pixels, it is possible to make a camera that only needs one pixel. This Review details the working principle, advantages, technical considerations and future potential of single-pixel imaging.

A second harmonic with a conversion efficiency of 0.049% W⁻¹, originating from surface nonlinearity and bulk multipole response in a silica whispering-gallery microcavity, is observed with a continuous-wave pump power below 1 mW.

A soliton microcomb as an astronomical spectrograph calibrator is presented. It can ultimately have a footprint of a few cubic centimetres, and reduced weight and power consumption, attractive for precision radial velocity measurement.

A microphotonic astrocomb is demonstrated via temporal dissipative Kerr solitons in photonic-chip-based silicon nitride microresonators with a precision of 25 cm s^–1 (radial velocity equivalent), useful for Earth-like planet detection and cosmological research.

Coupled lithium niobate ring resonators enable control of a ‘photonic molecule’ by programmed microwave signals. An on-demand optical storage and retrieval system is demonstrated.

A terawatt picosecond CO₂ laser beam is shown to form a centimetre-scale-diameter filament in air that is capable of carrying several joules of energy.

Five wire lasers are phase-locked by a strong coupling and form a coupled cavity. The lasing frequency is around 3.8 THz and is continuously tunable by 10 GHz. A continuous-wave output power of 50–90 mW and beam divergence of ∼10° are achieved.

The absolute phase difference of the harmonic emission of Ar, Ne and He atoms is measured by XUV interferometry with temporal resolution of 6 as. This measurement provides a direct insight into the quantum properties of the photoelectron wavefunctions.

Brillouin lasing with 0.7 Hz fundamental linewidth is observed by optically exciting a monolithic bus–ring Si₃N₄ waveguide resonator. The Brillouin laser is applied to an optical gyroscope and a low phase-noise photonic microwave oscillator.