Research

Quantum control of flying doughnut terahertz pulses

The ability to manipulate the multiple properties of light diversifies light-matter interaction and light-driven applications. Here, using quantum control, we introduce an approach that enables the amplitude, sign, and even configuration of the generated light fields to be manipulated in an all-optical manner. Following this approach, we demonstrate the generation of “flying doughnut” terahertz (THz) pulses. We show that the single-cycle THz pulse radiated from the dynamic ring current has an electric field structure that is azimuthally polarized and that the space- and time-resolved magnetic field has a strong, isolated longitudinal component. We apply the flying doughnut pulse for a spectroscopic measurement of the water vapor in ambient air. Pulses such as these will serve as unique probes for spectroscopy, imaging, telecommunications, and magnetic materials.

Reconfigurable electronic circuits for magnetic fields controlled by structured light

Dynamic control over the conduction band electrons of a semiconductor is a central technological pursuit. Beyond electronic circuitry, flexible control over the spatial and temporal character of semiconductor currents enables precise spatiotemporal structuring of magnetic fields. Despite their importance in science and technology, the control of magnetic fields at the micrometre spatial scale and femtosecond temporal scale using conventional electromagnets remains challenging. Here, we apply structured light beams to interfering photoexcitation pathways in gallium arsenide to sculpt the spatial and momentum configuration of its conduction band population. Programmable control over several hundred micrometre-scale current elements is achieved by manipulating the wavefronts of an optical beam using a spatial light modulator, enabling vast flexibility in the excited current patterns. Using this platform, we demonstrate dynamic optoelectronic interconnects, circuits for spatially tailored magnetic fields and magnetic field lattices.

Reconfigurable terahertz metasurfaces coherently controlled by wavelength-scale-structured light

Structuring light–matter interaction at a deeply subwavelength scale is fundamental to optical metamaterials and metasurfaces. Conventionally, the operation of a metasurface is determined by the collective electric polarization response of its lithographically defined structures. The inseparability of electric polarization and current density provides the opportunity to construct metasurfaces from current elements instead of nanostructures. Here, we realize metasurfaces using structured light rather than structured materials. Using coherent control, we transfer structure from light to transient currents in a semiconductor, which act as a source for terahertz radiation. Aspatial light modulator is used to control the spatial structure of the currents and the resulting terahertzradiation with a resolution of 5.6 ± 0.8 μm, or approximately λ/54 at a frequency of 1 THz. The independence of the currentsfrom any predefined structures and the maturity of spatial light modulator technology enable this metasurface to be reconfigured with unprecedented flexibility.