Ultra-subwavelength phase-sensitive Fano-imaging of localized photonic modes

Photonic and plasmonic devices rely on nanoscale control of the local density of optical states(LDOS)in dielectric and metallic environments.The tremendous progress in designing and tailoring the electric LDOS of nano-resonators requires an investigation tool that is able to access the detailed features of the optical localized resonant modes with deep-subwavelength spatial resolution.This scenario has motivated the development of different nanoscale imaging techniques.Here,we prove that a technique involving the combination of scanning near-field optical microscopy with resonant scattering spectroscopy enables imaging the electric LDOS in nano-resonators with outstanding spatial resolution(λ/19)by means of a pure optical method based on light scattering.Using this technique,we investigate the properties of photonic crystal nanocavities,demonstrating that the resonant modes appear as characteristic Fano line shapes,which arise from interference.Therefore,by monitoring the spatial variation of the Fano line shape,we locally measure the phase modulation of the resonant modes without the need of external heterodyne detection.This novel,deep-subwavelength imaging method allows us to access both the intensity and the phase modulation of localized electric fields.Finally,this technique could be implemented on any type of platform,being particularly appealing for those based on non-optically active material,such as silicon,glass,polymers,or metals.

Terahertz structured light:nonparaxial Airy imaging using silicon diffractive optics

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.