Terahertz structured light: nonparaxial Airy imaging using silicon diffractive optics

Abstract

Structured light – electromagnetic waves with a strong spatial inhomogeneity of amplitude, phase, and polarization – has occupied far-reaching positions in both optical research and applications. Terahertz (THz) waves, due to recent innovations in photonics and nanotechnology, became so robust that it was not only implemented in a wide variety of applications such as communications, spectroscopic analysis, and non-destructive imaging, but also served as a low-cost and easily implementable experimental platform for novel concept illustration. In this work, we show that structured nonparaxial THz light in the form of Airy, Bessel, and Gaussian beams can be generated in a compact way using exclusively silicon diffractive optics prepared by femtosecond laser ablation technology. The accelerating nature of the generated structured light is demonstrated via THz imaging of objects partially obscured by an opaque beam block. Unlike conventional paraxial approaches, when a combination of a lens and a cubic phase (or amplitude) mask creates a nondiffracting Airy beam, we demonstrate simultaneous lensless nonparaxial THz Airy beam generation and its application in imaging system. Images of single objects, imaging with a controllable placed obstacle, and imaging of stacked graphene layers are presented, revealing hence potential of the approach to inspect quality of 2D materials. Structured nonparaxial THz illumination is investigated both theoretically and experimentally with appropriate extensive benchmarks. The structured THz illumination consistently outperforms the conventional one in resolution and contrast, thus opening new frontiers of structured light applications in imaging and inverse scattering problems, as it enables sophisticated estimates of optical properties of the investigated structures.

Holographic THz Beam Generation by Nonlinear Plasmonic Metasurface Emitters

“…To benchmark the imaging performance of the two beam profiles under study, the sampling targets consist of 3 vertical slits, which are routinely used in THz imaging experiments . Here, the width of the slits remained constant ( w = λ 0 ), while the imaging performance was evaluated for various periodicities P between the slits.…”

“…In this regard, the adoption of structured light has fundamentally shaped recent progress in science and technology. For example, in the THz regime, structured illumination facilitates the emission of spatially tailored and nondiffracting beams, allowing for high resolution imaging, microscopy, and metrology schemes. – In addition, electromagnetic waves carrying structured orbital angular momentum may promote the advancement of fast and secure optical communication systems. , To effectively control and shape the THz emission, both passive and active configurations have been comprehensively studied over the years. Passive components such as diffractive optical elements provide various degrees of freedom on the post-generation shaping of the emitted wavefront. , However, inherent material losses result in limitations to the operational bandwidth and difficulties in the integration to on-chip designs, introducing engineering constraints to the design of THz systems.…”

“…To benchmark the imaging performance of the two beam profiles under study, the sampling targets consist of 3 vertical slits, which are routinely used in THz imaging experiments. 12 Here, the width of the slits remained constant (w = λ 0 ), while the imaging performance was evaluated for various periodicities P between the slits. As presented in Figure 5b,c, sampling with a sinc function resulting from the Top-Hat beam yields enhanced imaging resolution along the axis of structured illumination, allowing distinction between imaging targets with periodicities as low as 2.5λ 0 .…”

All‐Dielectric Integrated Meta‐Antenna Operating in 6G Terahertz Communication Window

“…[37] All-dielectric terahertz metagratings have been used in high-efficiency manipulation of diffraction distribution. [38] The all-dielectric terahertz metalenses have been proposed for flexible manipulation of orbital angular momentum waves, [39][40][41] generation of Airy beam, [42] spinmultiplexed controls, [43,44] achromatic focusing, [45] etc. A varifocal 6G meta-device with a fully tunable range of focal spots is designed by the meta-antennas with reasonably incorporating and rotating several phase profiles.…”

Fluorinated graphene grating metasurface for terahertz dark state excitation

“…The explosive growth of interest to exploring the Terahertz (THz) range stimulates further search for new, relatively cheap, scalable, compact, fast, tunable THz components (polarizers, modulators, filters, focusing elements) that can be easily integrated with the existing systems [1,2]. Today, THz optics is based in large extent on the periodic metal metasurfaces, sensitive to the phase and polarization of the incident radiation [3][4][5][6][7][8][9][10].…”