Spiral Field Generation in Smith-Purcell Radiation by Helical Metagratings

Moving electrons interacting with media can give rise to electromagnetic radiations and has been emerged as a promising platform for particle detection,spectroscopies,and free-electron lasers.In this letter,we investigate the Smith-Purcell radiation from helical metagratings,chiral structures similar to deoxyribonucleic acid(DNA),in order to understand the interplay between electrons,photons,and object chirality.Spiral feld patterns can be generated while introducing a gradient azimuthal phase distribution to the induced electric dipole array at the cylindrical interface.Experimental measurements show efcient control over angular momentum of the radiated feld at microwave regime,utilizing a phased electromagnetic dipole array to mimic moving charged particles.Te angular momentum of the radiated wave is determined solely by the handedness of the helical structure,and it thus serves as a potential candidate for the detection of chiral objects.Our fndings not only pave a way for design of orbital angular momentum free-electron lasers but also provide a platform to study the interplay between swif electrons with chiral objects.

Ultrawideband chromatic aberration-free meta-mirrors

Chromatic aberration-free meta-devices(e.g.,achromatic meta-devices and abnormal chromatic meta-devices)play an essential role in modern science and technology.However,current efforts suffer the issues of low efficiency,narrow operating band,and limited wavefront manipulation capability.We propose a general strategy to design chromatic aberration-free meta-devices with high-efficiency and ultrabroadband properties,which is realized by satisfying the key criteria of desirable phase dispersion and high reflection amplitudes at the target frequency interval.The phase dispersion is tuned successfully based on a multiresonant Lorentz model,and high reflection is guaranteed by the presence of the metallic ground.As proof of the concept,two microwave meta-devices are designed,fabricated,and experimentally characterized.An achromatic meta-mirror is proposed within 8 to 12 GHz,and another abnormal chromatic meta-mirror can tune the reflection angle as a linear function.Both meta-mirrors exhibit very high efficiencies(85%to 94%in the frequency band).Our findings open a door to realize chromatic aberration-free meta-devices with high efficiency and wideband properties and stimulate the realizations of chromatic aberration-free metadevices with other functionalities or working at higher frequency.

Direct current remote cloak for arbitrary objects

Hiding an arbitrary object with a cloak at a distance from an object is of great significance in scientific research,but remains unrealized as a practical device.In this paper,we propose the first experimental realization of a remote cloaking device that makes any object located at a certain distance invisible at direct current(DC)frequency.A negative resistor network with active elements is used to achieve the remote function of the DC cloak.Based on this network,the cloak can remotely generate a hidden region without distorting the currents far from the cloaked region.The experimental results show that any object in the hidden region is invisible to a DC detector.Our cloak does not require any knowledge of the hidden object.The experimental demonstration shows the superiority of this remote cloaking device,which may find potential applications in medical or geologic research.

Negative refraction of ultra-squeezed in-plane hyperbolic designer polaritons

The in-plane negative refraction of high-momentum(i.e.,high-k)photonic modes could enable many applications such as imaging,focusing,and waveguiding in a planar platform at deep-subwavelength scales.However,its practical implementation in experiments remains elusive so far.Here we propose a class of hyperbolic metasurfaces,which is characterized by an anisotropic magnetic sheet conductivity and can support the in-plane ultrahigh-k magnetic designer polaritons.Based on such metasurfaces,we report the experimental observation of the all-angle negative refraction of designer polaritons at extremely deep-subwavelength scales.Moreover,we directly visualize the designer polaritons with hyperbolic dispersions.Importantly,for these hyperbolic polaritons,we find that their squeezing factor is ultra-large.To be specific,it can be up to 129 in the experiments,an ultra-high value exceeding those in naturally hyperbolic materials.This work may pave a way toward exploring the extremely high confinement and unusual propagation of magnetic designer polaritons over monolayer or twisted bilayer hyperbolic metasurfaces.