Spoiled perishable products, such as food and drugs exposed to inappropriate temperature, cause million illnesses every year. Risks range from intoxication due to pathogen-contaminated edibles, to suboptimal potency of temperature-sensitive vaccines. High-performance and low-cost indicators are needed, based on conformable materials whose properties change continuously and irreversibly depending on the experienced time-temperature profile. However, these systems can be limited by unclear reading, especially for colour-blind people, and are often difficult to be encoded with a tailored response to detect excess temperature over varying temporal profiles. Here we report on optically-programmed, non-colorimetric indicators based on nano-textured non-wovens encoded by their cross-linking degree. This combination allows a desired time-temperature response to be achieved, to address different perishable products. The devices operate by visual contrast with ambient light, which is explained by backscattering calculations for the complex fibrous material. Optical nanomaterials with photo-encoded thermal properties might establish new design rules for intelligent labels.

Optomechanics deals with the control and applications of mechanical effects of light that stems from the redistribution of photon momenta in light scattering. As an example, light-induced levitation of an infinitesimally small dipolar particle is expected in front of epsilon-near-zero (ENZ) metamaterials. However, a theoretical understanding of these effects on single-material and multi-material larger particles is still lacking. Here, we investigate, analytically and numerically, optical forces on polarizable particles with size ranging from 20 nm to a 1 μm in proximity of ENZ metamaterials. We look at the general features of the repulsive-attractive optomechanics from the nano to the microscale exploiting different theoretical methods (dipole approximation, finite elements calculations, transition (T-)matrix). We discuss the role of realistic layered materials, as our ENZ substrate, on optical forces and analyze the influence of composition and shape by studying a range of complex particles (dielectric, core-shell, plasmonic ellipsoids). Physical insights into the results are discussed and future research directions are forecasted. Our results provide possibilities in exploiting engineered materials and surfaces for the manipulation and tailoring of light-induced forces in optomechanics.

Cosmic dust plays a dominant role in the universe, especially in the formation of stars and planetary systems. Furthermore, the surface of cosmic dust grains is the benchwork where molecular hydrogen and simple organic compounds are formed. We manipulate individual dust particles in a water solution by contactless and noninvasive techniques such as standard optical and Raman tweezers, to characterize their response to mechanical effects of light (optical forces and torques) and to determine their mineral compositions. Moreover, we show accurate optical force calculations in the T-matrix formalism highlighting the key role of composition and complex morphology in the optical trapping of cosmic dust particles. This opens perspectives for future applications of optical tweezers in curation facilities for sample-return missions or in extraterrestrial environments.

Optical tweezers are powerful tools based on focused laser beams. They are able to trap, manipulate, and investigate a wide range of microscopic and nanoscopic particles in different media, such as liquids, air, and vacuum. Key applications of this contactless technique have been developed in many fields. Despite this progress, optical trapping applications to planetary exploration are still to be developed. Here we describe how optical tweezers can be used to trap and characterize extraterrestrial particulate matter. In particular, we exploit light scattering theory in the T-matrix formalism to calculate radiation pressure and optical trapping properties of a variety of complex particles of astrophysical interest. Our results open perspectives in the investigation of extraterrestrial particles on our planet, in controlled laboratory experiments, aiming forspace tweezersapplications: optical tweezers used to trap and characterize dust particles in space or on planetary bodies surface.

Recently, acoustic tweezers based on an array of ultrasonic transducers have been reported taking inspiration from holographic optical tweezers. In the latter technique, the calibration of the optical trap is an essential procedure to obtain the trap stiffnesses. On the contrary, in the case of acoustic tweezers the calibration of the acoustic forces is seldom carried out. To cover this gap, in this work we adapt the calibration protocols employed in optical tweezers to acoustic tweezers based on arrays of ultrasonic transducers. We measure trap stiffnesses in the mN/m range that are consistent with theoretical estimates obtained by calculations of the acoustic radiation forces based on the Gor’kov potential. This work gives a common framework to the optical and acoustic manipulation communities, paving the way to a consistent calibration of hybrid acousto-optical setups.

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