Challenges on optical printing of colloidal nanoparticles

While colloidal chemistry provides ways to obtain a great variety of nanoparticles with different shapes, sizes, material compositions, and surface functions, their controlled deposition and combination on arbitrary positions of substrates remain a considerable challenge. Over the last ten years, optical printing arose as a versatile method to achieve this purpose for different kinds of nanoparticles. In this article, we review the state of the art of optical printing of single nanoparticles and discuss its strengths, limitations, and future perspectives by focusing on four main challenges: printing accuracy, resolution, selectivity, and nanoparticle photostabilit

Spin Orbit interactions of light in the dipolar approximation

Resumen del trabajo presentado a la Spanish Conference on Nanophotonics (Conferencia Española de Nanofotónica-CEN), celebrada en Donostia-San Sebastián (España) del 3 al 5 de octubre de 2018.In addition to energy and linear momentum, a light wave carries angular momentum (AM), which has been traditionally splitted in spin (SAM) and orbital angular momentum (OAM). The AM re-distribution between these two components after scattering originates the spin-orbit interactions of light (SOI), which has attracted a great interest during the last decades. Among all the intriguing SOIs effects perhaps the most interesting is the appearance of optical mirages: a transversal displacement of a target localization after scattering. This apparent shift, induced by the AM exchange per photon, has been predicted and experimentally proved in a large variety of situations. These include SAM light impinging a dielectric surface, a single polarizability electric dipole and a high refractive index (HRI) Si sphere sustaining both electric and magnetic response. In the latter case, the optical mirage reaches its maximum value at backscattering when the scattering is dual, namely, when the helicity is preserved. Hence, it may be intuitive to suspect that the absorption, which is embedded in the electric and magnetic polarizabilities, together with other relevant optical properties, such as the particle size, kind of material or surrounding medium, may modify the optical mirage and therefore, the AM exchange per photon. However, as we demonstrate in this work, the key ingredient in the scattering pattern of the SOI per photon is nothing but the asymmetric factor, which contains all the significant optical properties. We present a general theory of spin-to-orbital conversion of angular momentum (AM) in the dipolar regime from the measurable (Stokes parameters representation) helicity density expression. Based on the conservation of the AM in the incident direction, as a consequence of the spherical symmetry, we prove that the asymmetry factor (g-factor) is the only relevant magnitude in the spin orbit interactions of light (SOI), independently of other detailed optical properties. This is verifiable via our universal spectra of both the helicity density and the spin angular momentum (SAM) in which any optical response, including absorptive effects, is intriguingly encoded.Peer reviewe

Enhanced spin-orbit optical mirages from dual nanospheres

Resumen del trabajo presentado a la Spanish Conference on Nanophotonics (Conferencia Española de Nanofotónica-CEN), celebrada en Donostia-San Sebastián (España) del 3 al 5 de octubre de 2018.Spin-orbit interaction of light can lead to the so-called optical mirages, i.e. a perceived displacement in the position of a particle due to the spiraling structure of the scattered light. In electric dipoles, the maximum displacement is subwavelength and does not depend on the optical properties of the scatterer. Here we will show that the optical mirage in high refractive index dielectric nanoparticles depends strongly on the ratio between electric and magnetic dipolar responses. When the dual symmetry is satisfied (at the first Kerker condition), there is a considerable enhancement (far above the wavelength) of the spin-orbit optical mirage which can be related to the emergence of an optical vortex in the backscattering direction.Peer reviewe

Data Processing Unit for Energy Saving in Computer Vision: Weapon Detection Use Case

The growth of the Internet has led to the emergence of servers that perform increasingly heavy tasks. Some servers must remain active 24 h a day, but the evolution of network cards has facilitated the use of Data Processing Units (DPUs) to reduce network traffic and alleviate server workloads. This capability makes DPUs good candidates for load alleviation in systems that perform continuous data processing when the data can be pre-filtered. Computer vision systems that use some form of artificial intelligence, such as facial recognition or weapon detection, tend to have high workloads and high power consumption, which is becoming increasingly costly. Reducing the workload is therefore desirable and possible in some scenarios. The main contributions of this study are threefold: (1) to explore the potential benefits of using a DPU to alleviate the workload of a 24-h active server; (2) to present a study that measures the workload reduction of a CCTV weapon detection system and evaluate its performance under different conditions. We observed a 43,123% reduction in workload over the 24 h of video used in the experimentation, reaching more than 98% savings during night hours, which significantly reduces system stress and has a direct impact on electrical energy expenditure; and (3) to provide a framework that can be adapted to other computer vision-based detection systems

Enhanced spin-orbit optical mirages from dual nanospheres

Spin-orbit interaction of light can lead to the so-called optical mirages, i.e., a perceived displacement in the position of a particle due to the spiraling structure of the scattered light. In electric dipoles, the maximum displacement is subwavelength and does not depend on the optical properties of the scatterer. Here we will show that the optical mirage in high refractive index dielectric nanoparticles depends strongly on the ratio between electric and magnetic dipolar responses. When the dual symmetry is satisfied (at the first Kerker condition), there is a considerable enhancement (far above the wavelength) of the spin-orbit optical mirage which can be related to the emergence of an optical vortex in the backscattering direction.This research was supported by the Spanish Ministerio de Economía y Competitividad (MICINN) and European Regional Development Fund (ERDF) Projects No. FIS2014-55987-P, No. FIS2015-69295-C3-3-P, and No. FIS2017-82804-P, by the Basque Dep. de Educación Project No. PI-2016-1-0041 and by the Basque Government ELKARTEK program (KK-2016/00030, KK-2017/00089). A.G.-E. received funding from the Fellows Gipuzkoa fellowship of the Gipuzkoako Foru Aldundia through FEDER “Una Manera de hacer Europa.

Data Processing Unit for Energy Saving in Computer Vision: Weapon Detection Use Case

The growth of the Internet has led to the emergence of servers that perform increasingly heavy tasks. Some servers must remain active 24 h a day, but the evolution of network cards has facilitated the use of Data Processing Units (DPUs) to reduce network traffic and alleviate server workloads. This capability makes DPUs good candidates for load alleviation in systems that perform continuous data processing when the data can be pre-filtered. Computer vision systems that use some form of artificial intelligence, such as facial recognition or weapon detection, tend to have high workloads and high power consumption, which is becoming increasingly costly. Reducing the workload is therefore desirable and possible in some scenarios. The main contributions of this study are threefold: (1) to explore the potential benefits of using a DPU to alleviate the workload of a 24-h active server; (2) to present a study that measures the workload reduction of a CCTV weapon detection system and evaluate its performance under different conditions. We observed a 43,123% reduction in workload over the 24 h of video used in the experimentation, reaching more than 98% savings during night hours, which significantly reduces system stress and has a direct impact on electrical energy expenditure; and (3) to provide a framework that can be adapted to other computer vision-based detection systems.Ministerio de Ciencia e Innovación PDC2021-121197Ministerio de Ciencia e Innovación PID2021-126359OB-I00European Commission ID2PPAC ID:10100725

Data Processing Unit for Energy Saving in Computer Vision: Weapon Detection Use Case

The growth of the Internet has led to the emergence of servers that perform increasingly heavy tasks. Some servers must remain active 24 h a day, but the evolution of network cards has facilitated the use of Data Processing Units (DPUs) to reduce network traffic and alleviate server workloads. This capability makes DPUs good candidates for load alleviation in systems that perform continuous data processing when the data can be pre-filtered. Computer vision systems that use some form of artificial intelligence, such as facial recognition or weapon detection, tend to have high workloads and high power consumption, which is becoming increasingly costly. Reducing the workload is therefore desirable and possible in some scenarios. The main contributions of this study are threefold: (1) to explore the potential benefits of using a DPU to alleviate the workload of a 24-h active server; (2) to present a study that measures the workload reduction of a CCTV weapon detection system and evaluate its performance under different conditions. We observed a 43,123% reduction in workload over the 24 h of video used in the experimentation, reaching more than 98% savings during night hours, which significantly reduces system stress and has a direct impact on electrical energy expenditure; and (3) to provide a framework that can be adapted to other computer vision-based detection systems.Ministerio de Ciencia e Innovación PID2021-126359OB-I00Ministerio de Ciencia e Innovación, Unión Europea PDC2021-121197-C2

Size-selective optical printing of silicon nanoparticles through their dipolar magnetic resonance

Silicon nanoparticles possess unique size-dependent optical properties due to their strong electric and magnetic resonances in the visible range. However, their widespread application has been limited, in comparison with other (e.g., metallic) nanoparticles, because their preparation on monodisperse colloids remains challenging. Exploiting the unique properties of Si nanoparticles in nano- A nd microdevices calls for methods able to sort and organize them from a colloidal suspension onto specific positions of solid substrates with nanometric precision. We demonstrate that surfactant-free silicon nanoparticles of a predefined and narrow (σ < 10 nm) size range can be selectively immobilized on a substrate by optical printing from a polydisperse colloidal suspension. The size selectivity is based on differential optical forces that can be applied on nanoparticles of different sizes by tuning the light wavelength to the size-dependent magnetic dipolar resonance of the nanoparticles