Genetically Synthesized Supergain Broadband Wire-Bundle Antenna

High-gain antennas are essential hardware devices, powering numerous daily applications, including distant point-to-point communications, safety radars, and many others. While a common approach to elevate gain is to enlarge an antenna aperture, highly resonant subwavelength structures can potentially grant high gain performances. The Chu-Harrington limit is a standard criterion to assess electrically small structures and those surpassing it are called superdirective. Supergain is obtained in a case when internal losses are mitigated, and an antenna is matched to radiation, though typically in a very narrow frequency band. Here we develop a concept of a spectrally overlapping resonant cascading, where tailored multipole hierarchy grants both high gain and sufficient operational bandwidth. Our architecture is based on a near-field coupled wire bundle. Genetic optimization, constraining both gain and bandwidth, is applied on a 24-dimensional space and predicts 8.81 dBi realized gain within a half-wavelength in a cube volume. The experimental gain is 6.15 with 13% fractional bandwidth. Small wire bundle structures are rather attractive for designing superscattering and superdirective structures, as they have a sufficient number of degrees of freedom to perform an optimization, and, at the same time rely on simple fabrication-tolerant layouts, based on low-loss materials. The developed approach can be applied to low-frequency (e.g., kHz-MHz) applications, where miniaturization of wireless devices is highly demanded

Long-range optical trapping and binding of microparticles in hollow-core photonic crystal fibre.

Optically levitated micro- and nanoparticles offer an ideal playground for investigating photon-phonon interactions over macroscopic distances. Here we report the observation of long-range optical binding of multiple levitated microparticles, mediated by intermodal scattering and interference inside the evacuated core of a hollow-core photonic crystal fibre (HC-PCF). Three polystyrene particles with a diameter of 1 µm are stably bound together with an inter-particle distance of ~40 μm, or 50 times longer than the wavelength of the trapping laser. The levitated bound-particle array can be translated to-and-fro over centimetre distances along the fibre. When evacuated to a gas pressure of 6 mbar, the collective mechanical modes of the bound-particle array are able to be observed. The measured inter-particle distance at equilibrium and mechanical eigenfrequencies are supported by a novel analytical formalism modelling the dynamics of the binding process. The HC-PCF system offers a unique platform for investigating the rich optomechanical dynamics of arrays of levitated particles in a well-isolated and protected environment.This work was supported by Max Planck Society. R. Z. acknowledges funding from the Cluster of Excellence "Engineering of Advanced Materials" at the Friedrich-Alexander University in Erlangen, Germany

Optically Controlled Dissolution Kinetics of Vaterite Microcapsules: Toward Novel Crystal Growth Strategies

Controllable continuous release of functional materials from capsules is one of the unmet functions of theragnosis particles; on this way, understanding cargo–fluid interactions in vitro is an essential milestone. We develop a flexible platform to investigate single particle–fluid interactions utilizing a glass micropipette as a highly localized flow source around an optically trapped particle. In proof-of-concept experiments, this microparticle is sensitive to local microflow distribution, thus serving as a probe. The very same flows are capable of the particle rotating (i.e., vaterite drug cargo) at frequencies dependent on the mutual particle–pipette position. Platform flexibility comes from different interactions of a tweezer (optical forces) and a pipette (mechanical/hydrodynamical) with a microparticle, which makes this arrangement an ideal microtool. We studied the vaterite dissolution kinetics and demonstrated that it can be controlled on demand, providing a wide cargo release dynamic rate. Our results promote the use of inorganic mesoporous nanoparticles as a nanomedicine platform

Gilded vaterite optothermal transport in a bubble

Abstract Laser beams, capable of controlling the mechanical motion of micron-scale objects, can serve as a tool, enabling investigations of numerous interaction scenarios under full control. Beyond pure electromagnetic interactions, giving rise to conventional gradient forces and radiation pressure, environment-induced thermal effects can play a role and, in certain cases, govern the dynamics. Here we explore a thermocapillary Marangoni effect, which is responsible for creating long-range few hundreds of nano-Newton forces, acting on a bubble around a ‘gilded vaterite’ nanoparticle. Decorating calcium carbonate spherulite (the vaterite) with gold nanoseeds allows tuning its optical absorption and, as a result, controlling its temperature in a solution. We demonstrate that keeping a balance between electromagnetic and thermal interactions allows creating of a stable micron-scale bubble around the particle and maintaining its size over time. The bubbles are shown to remain stable over minutes even after the light source is switched off. The bubbles were shown to swim toward a laser focus for over 400-µm distances across the sample. Optothermal effects, allowing for efficient transport, stable bubble creation, and particle–fluid interaction control, can grant nano-engineered drug delivery capsules with additional functions toward a theragnostic paradigm shift

Optothermal Needle‐Free Injection of Vaterite Nanocapsules

Abstract The propulsion and acceleration of nanoparticles with light have both fundamental and applied significance across many disciplines. Needle‐free injection of biomedical nano cargoes into living tissues is among the examples. Here a new physical mechanism of laser‐induced particle acceleration is explored, based on abnormal optothermal expansion of mesoporous vaterite cargoes. Vaterite nanoparticles, a metastable form of calcium carbonate, are placed on a substrate, underneath a target phantom, and accelerated toward it with the aid of a short femtosecond laser pulse. Light absorption followed by picosecond‐scale thermal expansion is shown to elevate the particle's center of mass thus causing acceleration. It is shown that a 2 µm size vaterite particle, being illuminated with 0.5 W average power 100 fsec IR laser, is capable to overcome van der Waals attraction and acquire 15m sec−1 velocity. The demonstrated optothermal laser‐driven needle‐free injection into a phantom layer and Xenopus oocyte in vitro promotes the further development of light‐responsive nanocapsules, which can be equipped with additional optical and biomedical functions for delivery, monitoring, and controllable biomedical dosage to name a few

Optoacoustic Effect in a Hybrid Multilayered Membrane Deposited on a Hollow-Core Microstructured Optical Waveguide

Modern imaging technologies, including optoacoustic endoscopy, are based on the optoacoustic effect. Much promise is offered by the all-optical fiber-based approach, because fiber has a miniature cross section, is highly sensitive, and can be used in a variety of imaging and therapeutic techniques. We developed a probe based on a hollow-core microstructured optical waveguide (HC-MOW) with a hybrid nanostructured membrane. The membrane consisted of a free-standing single-walled carbon nanotube film and a Bragg reflector, which can be used as a source and a detector of ultrasound. Membrane vibrations were excited with an IR laser pulse and were read out by recording the intensity of the reflected visible CW laser light. We explained the nature of the intensity modulation of the reflected light and supported our explanation with numerical simulations of the membrane’s vibration eigenfrequencies and thermal distribution. The membrane vibrations were also observed with raster-scanning optoacoustic mesoscopy. The transmittance of the HC-MOW between 400 nm and 6.5 μm and that of the hybrid nanostructured membrane in the NIR range enable potential optoacoustic sensing in the IR fingerprint region of biomolecules. This permits the optoacoustic probe to be used for medical endoscopic purposes

Multispectral sensing of biological liquids with hollow-core microstructured optical fibres

The state of the art in optical biosensing is focused on reaching high sensitivity at a single wavelength by using any type of optical resonance. This common strategy, however, disregards the promising possibility of simultaneousmeasurements of a bioanalyte’s refractive index over a broadband spectral domain. Here, we address this issue by introducing the approach of in-fibre multispectral optical sensing (IMOS). The operating principle relies on detecting changes in the transmission of a hollow-core microstructured optical fibre when a bioanalyte is streamed through it via liquid cells. IMOS offers a unique opportunity to measure the refractive index at 42 wavelengths, with a sensitivityup to ~3000 nm per refractive index unit (RIU) and a figure of merit reaching 99 RIU−1 in the visible and near-infra-red spectral ranges. We apply this technique to determine the concentration and refractive index dispersion for bovineserum albumin and show that the accuracy meets clinical need