A self-healing multispectral transparent adhesive peptide glass.

Despite its disordered liquid-like structure, glass exhibits solid-like mechanical properties1. The formation of glassy material occurs by vitrification, preventing crystallization and promoting an amorphous structure2. Glass is fundamental in diverse fields of materials science, owing to its unique optical, chemical and mechanical properties as well as durability, versatility and environmental sustainability3. However, engineering a glassy material without compromising its properties is challenging4-6. Here we report the discovery of a supramolecular amorphous glass formed by the spontaneous self-organization of the short aromatic tripeptide YYY initiated by non-covalent cross-linking with structural water7,8. This system uniquely combines often contradictory sets of properties; it is highly rigid yet can undergo complete self-healing at room temperature. Moreover, the supramolecular glass is an extremely strong adhesive yet it is transparent in a wide spectral range from visible to mid-infrared. This exceptional set of characteristics is observed in a simple bioorganic peptide glass composed of natural amino acids, presenting a multi-functional material that could be highly advantageous for various applications in science and engineering.

External chirality enhancing downconversion in a waveguide-coupled nonlinear plasmonic metasurface.

Metasurfaces, typically constructed from spatial arrangements of localized building blocks, can enhance light-matter interactions through local field enhancement or by coherent coupling to extended photonic modes. Recent works have explored how guided mode resonances influence the performance of nonlinear metasurfaces. Here we investigate the modal impact on difference-frequency generation in a waveguide-coupled metasurface platform. The system is constructed from gold split-ring resonators on a high-index TiO2 waveguide. We find that a symmetric configuration of the metasurface's localized modes and the extended waveguide modes lead to a modest enhancement of the downconversion process. However, when the mirror symmetry of the localized modes with respect to the guided mode propagation breaks, it introduces external chirality. This enables coupling to a higher quality mode, resulting in a 70-fold enhancement of the difference-frequency generation. The capacity to manipulate the nonlocal modes through the design offers broader control over the interaction and new avenues to tailor the nonlinear processes.

Generating Angular-Varying Time Delays of THz Pulses via Direct Space-to-Time Mapping of Metasurface Structures.

We experimentally demonstrate the generation of double terahertz (THz) pulses with tailored angular-dependent time delays from a nonlinear metasurface excited by a near-infrared femtosecond pulse. The tailored temporal properties of the generated pulses emerge from a direct mapping of the nonlinear spatial response of the metasurface to the emitted THz temporal profile. We utilize the Pancharatnam-Berry phase to implement symmetric and antisymmetric metasurface configurations and show that the emitted patterns present spatiotemporal "X-shaped" profiles after collimation by a parabolic mirror, with angular-dependent pulse delays corresponding to the intended design. In addition, we show that the addition of polarization multiplexing presents the opportunity to achieve a full range of elliptical THz polarizations. Double pulse generation and spatiotemporal shaping of THz waves in general show potential for THz spectroscopy and molecular dynamics applications, particularly in pump-probe experiments.

Nonlinear THz Generation through Optical Rectification Enhanced by Phonon-Polaritons in Lithium Niobate Thin Films.

We investigate nonlinear THz generation from lithium niobate films and crystals of different thicknesses by optical rectification of near-infrared femtosecond pulses. A comparison between numerical studies and polarization-resolved measurements of the generated THz signal reveals a 2 orders of magnitude enhancement in the nonlinear response compared to optical frequencies. We show that this enhancement is due to optical phonon modes at 4.5 and 7.45 THz and is most pronounced for films thinner than 2 µm where optical-to-THz conversion is not limited by self-absorption. These results shed new light on the employment of thin film lithium niobate platforms for the development of new integrated broadband THz emitters and detectors. This may also open the door for further control (e.g., polarization, directivity, and spectral selectivity) of the process in nanophotonic structures, such as nanowires and metasurfaces, realized in the thin film platform. We illustrate this potential by numerically investigating optical-to-THz conversion driven by localized surface phonon-polariton resonances in sub-wavelength lithium niobate rods.

Holographic THz Beam Generation by Nonlinear Plasmonic Metasurface Emitters.

The advancement of terahertz (THz) technology hinges on the progress made in the development of efficient sources capable of generating and shaping the THz emission. However, the currently available THz sources provide limited control over the generated field. Here, we use near-field interactions in nonlinear Pancharatnam-Berry phase plasmonic metasurfaces to achieve deep subwavelength, precise, and continuous control over the local amplitude of the emitted field. We show that this new ability can be used for holographic THz beam generation. Specifically, we demonstrate the generation of precisely shaped Hermite-Gauss, Top-Hat, and triangular beams. We show that using this method, higher-order modes are completely suppressed, indicating optimal nonlinear diffraction efficiency. In addition, we demonstrate the application of the generated structured beams for obtaining enhanced imaging resolution and contrast. These demonstrations hold immense potential to address challenges associated with a broad range of new applications employing THz technology.

Electrically and all-optically switchable nonlocal nonlinear metasurfaces.

Nonlocal effects on metasurfaces play an important role to achieve high-Q spectral selectivity, beneficial for development of multifunctional, multispectral integrated optics. In addition, they enhance the optical interaction and promote a variety of nonlinear effects, including frequency conversion and stimulated scattering. Active tuning of nonlocal nonlinearity is highly desirable for sensing and signal processing but was hardly explored until now. Here, we show drastic electric and all-optical tunability of nonlocal second-harmonic generation (SHG) from nonlinear metasurface, functionalized with a twisted nematic liquid-crystal (LC) layer. The addition of LC results in the emergence of strong nonlocal SHG, due to a surface lattice resonance of the system. We demonstrate a notable enhancement of SHG on resonance, more than 25 dB electrical switching amplitude, and all-optically induced phase transition imprinted on SHG. Our results on dynamic nonlocal effects introduce a very promising route for active nonlinear optical metadevices at the nanoscale.

Rayleigh anomaly induced phase gradients in finite nanoparticle chains.

Collective optical interactions in infinite nanoparticle arrays have been studied intensively over the past decade. However, analysis of finite arrays has received significantly less attention. Here, we theoretically and numerically show that the collective interaction in finite nanoparticle chains can support phase gradients that shift the diffraction pattern with respect to infinite chains. Specifically, we demonstrate that this phenomenon occurs for resonating nanoparticles in a narrow spectral range around the Rayleigh anomaly condition, i.e., when a certain diffraction order radiates at a grazing angle. This reveals that the Rayleigh anomaly, which is associated with intensity changes, can also induce angular anomalies in finite arrays. To study the effect theoretically, we develop a novel analytical approach based on the discrete dipole approximation. Within this framework, we find an approximate closed-form solution to the particles' dipole moments. We show that our solution can be expressed in two different ways, one based on a combinatorial calculation, and the other on a recursive calculation, and discuss the unique physical interpretation emerging from each of them. Our results are of potential importance in a wide range of practical applications from LIDARs to beam shaping schemes.

Enhancing THz emission from nonlinear metasurfaces by a Bragg perfect absorber.

Nonlinear plasmonic metasurfaces were demonstrated recently as ultracompact tetrahertz (THz) sources, emitting relatively strong single-cycle THz pulses after femtosecond laser illumination. There has been great progress in their ability to generate controlled THz wavepackets; however, their overall emission strength has not yet been optimized. Here we numerically show that by designing a Bragg assisted perfect absorber we can improve the coupling of the pumping laser to the nonlinear metasurface. This results in over an order of magnitude enhancement of the THz signal. Moreover, we show that this method can be combined with other independent optimization schemes to further enhance the radiated THz, reaching over two orders of magnitude emission enhancement compared with previously studied plasmonic metasurfaces.

Organic Kainate Single Crystals for Second-Harmonic and Broadband THz Generation.

Organic crystals with unique nonlinear optical properties have been attracting attention owing to their capability to outperform their conventional nonorganic counterparts. Since nonlinear material responses are linked to a crystal's internal microscopic structure, molecular engineering of maximally unharmonic quantum potentials can boost macromolecular susceptibilities. Here, large-scale kainic acid (kainate) single crystals were synthesized, and their linear and nonlinear optical properties were studied in a broad spectral range, spanning the visible to THz spectral regions. The non-centrosymmetric zwitterionic crystallization, molecular structure, and intermolecular arrangement were found to act as additive donor-acceptor domains, enhancing the efficiency of the intrinsic second-order optical nonlinearity of this pure enantiomeric crystal. Molecular simulations and experimental analysis were performed to retrieve the crystals' properties. The crystals were predicted and found to have good transparency in a broad spectral range from the UV to the infrared (0.2-20 µm). Second-harmonic generation was measured for ultrashort pumping wavelengths between 800 and 2400 nm, showing an enhanced response around 600 nm. Broadband THz generation was demonstrated with a detection limited bandwidth of >8 THz along with emission efficiencies comparable to and prevailing those of commercial ZnTe crystals. The broadband nonlinear response and high transparency make kainate crystals extremely attractive for realizing a range of nonlinear optical devices.

THz Radiation Efficiency Enhancement from Metal-ITO Nonlinear Metasurfaces.

Strong single-cycle THz emission has been demonstrated from nonlinear plasmonic metasurfaces, when excited by femtosecond laser pulses. In order to invoke a higher nonlinear response, such metasurfaces have been coupled to thin indium-tin-oxide (ITO) films, which exhibit an epsilon-near zero (ENZ) behavior in the excitation wavelength range and enhance the nonlinear conversion. However, the THz conductivity of the ITO film also reduces the radiation efficiency of the meta-atoms constituting the metasurface. To overcome this, we etch the ITO layer around the plasmonic meta-atoms, which allows harnessing of the enhanced localized fields due to the ENZ behavior of the remaining ITO film, while improving the THz radiation efficiency. We report an increase of more than 1 order of magnitude in the emitted THz spectral power density, while the energy conversion efficiency approaches 10-6. This simple yet very effective fabrication scheme provides important progress toward increasing the range of applications of nonlinear plasmonic metasurface THz emitters.

The Role of Epsilon Near Zero and Hot Electrons in Enhanced Dynamic THz Emission from Nonlinear Metasurfaces.

We study theoretically and experimentally the nonlinear THz emission from plasmonic metasurfaces and show that a thin indium-tin oxide (ITO) film significantly affects the nonlinear dynamics of the system. Specifically, the presence of the ITO film leads to 2 orders of magnitude stronger THz emission compared to a metasurface on glass. It also shows a different power law, signifying different dominant emission mechanisms. In addition, we find that the hot-electron dynamics in the system strongly modify the coupling between the plasmonic metasurface and the free electrons in the ITO at the picosecond time scale. This results in striking dynamic THz emission phenomena that were not observed to date. Specifically, we show that the generated THz pulse can be shortened in time and thus broadened in frequency with twice the bandwidth compared to previous studies and to an uncoupled system. Our findings open the door to design efficient and dynamic metasurface THz emitters.

Second-Harmonic Enhancement from a Nonlinear Plasmonic Metasurface Coupled to an Optical Waveguide.

Metasurfaces are commonly constructed from two-dimensional arrangements of nanoresonators. Coherent coupling of the nanoresonators through extended photonic modes of the metasurface results in a modified collective optical response, and enhances light-matter interactions. Here we experimentally demonstrate that strong collective resonances can arise also from coupling the metasurface to an optical waveguide. We explore the effect this waveguide-assisted collective interaction has on second-harmonic generation from the hybrid system. Our measurements indicate an enhancement factor of 8 for the transmitted second harmonic in comparison to incoherent collective scattering. In addition, complementary simulations predict about a 100-fold enhancement for the second harmonic that remains confined inside the waveguide. The ability to control the hybrid modes by the waveguide's design provides broader control over the formation of the collective interaction and new tools to tailor the nonlinear interactions. Our findings pave a promising direction to realize nonlinear photonic circuits with metasurfaces.

Terahertz Metagrating Emitters with Beam Steering and Full Linear Polarization Control.

We report the realization of broadband THz plasmonic metagrating emitters for simultaneous beam steering and all-optical linear polarization control. Two types of metagratings are designed and experimentally demonstrated. First, the plasmonic meta-atoms are arranged in a metagrating with a binary phase modulation which results in the nonlinear generation of THz waves to the ±1 diffraction orders, with complete suppression of the zeroth order. Complete tunability of the diffracted THz linear polarization direction is demonstrated through simple rotation of the pump polarization. Then, the concept of lateral phase shift is introduced into the design of the metagratings using interlaced phase gradients. By controlling the spatial shift of the submetagrating, we are able to continuously control the linear polarization states of the generated THz waves. This method results in a higher nonlinear diffraction efficiency relative to binary phase modulation. These functional THz metagratings show exciting promise to meet the challenges associated with the current diverse array of applications utilizing THz technology.

Dual Mobility hip replacement in hip fractures offer functional equivalence and a stability advantage - A case-controlled study.

BACKGROUND: Hip fracture is a common and serious injury in the elderly. Hip arthroplasty is the most frequently performed procedure for patients with an  intracapsular hip fracture. The majority of national guidelines recommend total hip arthroplasty (THA) for more active patients. Literature indicates significant stability advantages for dual mobility (DM) acetabular components in non-emergent scenarios. Evidence supporting the use of DM in hip fracture patients is limited. AIM: We set out to ascertain if DM implants offer stability and/or functional advantages over standard THA in patients with hip fracture. METHODS: We utilised our local National Hip Fracture Database to identify all patients undergoing either a standard or DM THA for hip fracture (n=477) We matched cohorts based on age, AMTS, mobility status pre-operatively, gender, ASA and source of admission. Our primary outcome of interest was functional status using the oxford hip score (OHS). Secondary outcome measures included  dislocation, fracture and deep infection requiring further surgery. RESULTS: 62 patient pairs were available for this study. Mean OHS for DM THA was 41.5 and for standard THA this was 42.7 (p=0.58). There were 4 dislocations in the standard THA group and 0 with DM THA. No difference was seen with infection or peri-prosthetic fracture. CONCLUSION: This study demonstrates functional equivalence between DM and standard THA. In addition it shows a trend towards less dislocation with DM THA. Cost savings from less instability may outweigh initial prosthesis costs. This study suggests a suitably powered RCT using instability as the primary outcome measure is indicated.

Functional THz emitters based on Pancharatnam-Berry phase nonlinear metasurfaces.

Recent advances in the science and technology of THz waves show promise for a wide variety of important applications in material inspection, imaging, and biomedical science amongst others. However, this promise is impeded by the lack of sufficiently functional THz emitters. Here, we introduce broadband THz emitters based on Pancharatnam-Berry phase nonlinear metasurfaces, which exhibit unique optical functionalities. Using these new emitters, we experimentally demonstrate tunable linear polarization of broadband single cycle THz pulses, the splitting of spin states and THz frequencies in the spatial domain, and the generation of few-cycle pulses with temporal polarization dispersion. Finally, we apply the ability of spin control of THz waves to demonstrate circular dichroism spectroscopy of amino acids. Altogether, we achieve nanoscale and all-optical control over the phase and polarization states of the emitted THz waves.

Nonlinear Plasmonic Metasurface Terahertz Emitters for Compact Terahertz Spectroscopy Systems.

Nonlinear plasmonic metasurfaces provide new and promising means to produce broadband terahertz (THz) radiation, due to their compact size and functionalities beyond those achievable with conventional THz emitters. However, they were driven to date only by amplified laser systems, which are expensive and have a large footprint, thus limiting the range of their potential applications. Here we study for the first time the possibility to drive metasurface emitters by low-energy near-infrared femtosecond pulses. We observe broadband THz emission from 40 nm thick metasurfaces and achieve near-infrared to THz conversion efficiencies as high as those of 2500-fold thicker ZnTe crystals. We characterize the THz emission properties and use the metasurface emitter to perform a spectroscopic measurement of α-lactose monohydrate. These results show that nonlinear plasmonic metasurfaces are suitable for integration as emitters in existing compact THz spectroscopy and imaging systems, enhancing their functionalities, and opening the door for a variety of new applications.

Metasurface-based contact lenses for color vision deficiency: reply.

The filtering of overlapping spectral regions may be used to increase the observer's gamut in some cases. Therefore, metasurface-based contact lenses (M-CL) may improve the color coding for specific stimuli and deuteranomaly conditions. Here, we address the concerns made by Huertas et al. [Opt. Lett.45, 5117 (2020)OPLEDP0146-959210.1364/OL.394717], regarding the color perception improvement obtained by color filters, in general, and specifically by our M-CL, in case of deuteranomaly.

Tuning the phase and amplitude response of plasmonic metasurface etalons.

We study the optical response of plasmonic metasurface etalons in reflection. The etalons consist of a metallic mirror and a plasmonic metasurface separated by wavelength-scale dielectric spacer. We show that tuning the localized surface plasmon resonance and spacer thickness can be used to achieve both enhanced reflectivity and perfect absorption, in addition to full 2π range phase control, and tunable regions of normal and anomalous dispersion. We validate our claims by measuring the spectral reflection and phase response of metasurface etalons consisting aluminum nanodisks of different radii separated from an aluminum reflector by a SiO2 spacer. In addition, we use this approach to demonstrate a simple Hermite-Gaussian (HG) wavelength selective beam-shaping reflective mask. The concept can be further extended by using multilayers to obtain multi-functional elements.

Metasurface-based contact lenses for color vision deficiency.

We embed large-scale, plasmonic metasurfaces into off-the-shelf rigid gas permeable contact lenses and study their ability to serve as visual aids for color vision deficiency. In this study, we specifically address deuteranomaly, which is the most common class of color vision deficiency. This condition is caused by a redshift of the medium-type cone photoreceptor and leads to ambiguity in the color perception of red and green and their combinations. The effect of the metasurface-based contact lenses on the color perception was simulated using Commission Internationale de l'Eclairage (CIE) color spaces and conventional models of the human color-sensitive photoreceptors. Comparison between normal color vision and uncorrected and corrected deuteranomaly by the proposed element demonstrates the ability offered by the nanostructured contact lens to shift back incorrectly perceived pigments closer to the original pigments. The maximal improvement in the color perception error before and after the proposed correction for deuteranomaly is up to a factor of $\sim{10}$∼10. In addition, an Ishihara-based color test was also simulated, showing the contrast restoration achieved by the element, for deuteranomaly conditions.

Direct space to time terahertz pulse shaping with nonlinear metasurfaces.

We present a method for the generation of THz pulses with tailored temporal shape from nonlinear metasurfaces. The method is based on single-cycle THz emission by the metasurface inclusions. We show that the spatial amplitude and phase structure of the nonlinear response is mapped to the temporal shape of pulses emitted at certain angles. We specifically show a method for reconstruction of desired pulses, generation of few-cycles pulses with tailored carrier-envelope and all-optical control over the pulse shape by the pump pulse characteristics.