No abstract

In the current trend toward miniaturization, integrated micro-optical elements play a central role in the development of various applications including high-density data storage and imaging. In these operations, fine alignment and focus adjustment are usually performed mechanically, thus, limiting the accuracy, size and speed of devices. Here, we propose a novel reconfigurable microlens based on the engineering of the temperature distribution induced by a patterned plasmonic surface shined with a resonant nearinfrared light. The refractive index change generated in a surrounding thermo-optical material acts as an effective lens whose parameters are remotely adjusted by the control nearinfrared light. We demonstrate focal distance tunability of tens of microns with subnanometer accuracy along with timeresponses down to 200 μs. The applicability of this photothermal lens is proved in the framework of optical microscopy and adaptive optics.

A comparative study of different plasmonic nanoparticles with different morphologies (nanospheres and triangular nanoprisms) and metals (Ag and Au) was done in this work and applied to the ultrasensitive detection of aminoglutethimide (AGI) drug by surface enhanced Raman spectroscopy (SERS) and plasmon resonance. AGI is an aromatase inhibitor used as an antitumoral drug with remarkable pharmacological interest and also in illegal sport doping. The application of very sensitive spectroscopic techniques based on the localization of an electromagnetic field on plasmonic nanoparticles confirms the previous study of the adsorption of drugs onto a metal surface due to the near field character of these techniques. The adsorption of AGI on the above substrates was investigated at different pH values and surface coverages, and the results were analyzed on the basis of AGI/metal affinity, considering the interaction mechanism, the existence of two binding sites in AGI, and the influence of the interface on the adsorption in terms of surface charge due to the presence of other ions linked to the surface. Finally, a comparative quantitative detection of AGI was performed on both spherical and triangular nanoprism nanoparticles, and a limit of detection lower than those reported so far was deduced on the latter nanoparticles.

Visualisation and manipulation of nanoscale matter is one of the main and current challenges in nanosciences. To this aim, different techniques have been recently developed to non-invasively trap and manipulate nano-specimens, like nanoparticles or molecules. However, operating in air or vacuum still remains very challenging since most approaches are limited to a liquid environment. In this letter, we design and characterise a planar Paul trap optimised to trap and manipulate individual charged nanoparticles. This configuration offers competitive capabilities to manipulate nano-specimens in air or vacuum including in-plane integration, high trap confinement along with dynamical trap reconfiguration.Current research in nanotechnology demands tools to accurately and non-invasively manipulate objects at the nanoscale. Conventional optical tweezers (OTs) have these capabilities for micrometer sized objects and neutral atoms [1], but are inadequate for the intermediate size range (i.e. 1-100 nm size objects), mainly due to the strong decrease of optical forces with the particle's volume [2]. As an alternative, researchers have developed near field optical trapping schemes based on nanoplasmonics [3] and silicon photonics [4]. Such approaches allow stable trapping from single proteins [5] up to nanoparticles of a few tens of nanometers [6][7][8] and have recently allowed 3D manipulation [9]. Other alternatives are surface electrostatic traps [10] and the AntiBrownian Eletrophoretic trap (ABEL) [11,12]. However, all remain limited to a liquid environment and it still represents an important challenge to adapt this technology to other mediums, i.e. air or vacuum. Interestingly, the optical levitation of nanoparticles in high vacuum has appeared as an exquisite platform for several applications in force sensing and optomechanics [13][14][15][16][17]. However, photothermal damage strongly limits the nanoparticle's material, and typically only silica (very low absorption) is used. Yet, it would be very interesting to levitate other nanoparticles featuring internal energy level like colour centers [18][19][20].Originally used to trap ions, Paul traps (PTs)[21] can levitate charged nano-objects [22][23][24][25][26][27][28]. PTs found applications in various fields in physics [29,30], chemistry [31,32] and even biology [33,34]. They are based on a quadrupole potential originating from a RF time varying electrical field created by a set of properly arranged electrodes. The trajectory of the trapped object is described by the superposition of a fast driven oscillation at the frequency of the RF field called micromotion and a slower one called macromotion [35]. PTs electrodes * These authors contributed equally † johann.berthelot@fresnel.fr; Current address: CNRS, AixMarseille Universit, Centrale Marseille, Institut Fresnel, UMR 7249, 13013 Marseille, France ‡ romain.quidant@icfo.es designs can be challenging to fabricate and are usually bulky, hence complicating the trap loading and its optical interrogation. An interesting alt...

Contrary to most materials, graphene exhibits a negative thermal expansion coefficient (TEC), i.e it contracts when heated. This contraction is due to the thermal excitation of low energy out-ofplane vibration modes. These flexural modes have been reported to govern the electronic transport and the mechanical response of suspended graphene. In this work, we systematically investigate the influence of defects in the TEC of suspended graphene membranes. Controlled introduction of low densities of mono-vacancies reduces the graphene TEC, up to one order of magnitude for a defect density of 5 × 10 12 cm −2 . Our molecular dynamics simulations reproduce the observed trend and show that TEC reduction is due to the suppression of out-of-plane fluctuations caused by the strain fields created by mono-vacancies in their surrounding areas. These results highlight the key role of defects in the properties of "real-life" graphene, and pave the way for future proposals of electronic and mechanical defect engineering.

We investigate the nonlinear optical response of suspended 1D photonic crystal nanocavities fabricated on a silicon nitride chip. Strong thermo-optical nonlinearities are demonstrated for input powers as low as 2 µW and a self-sustained pulsing regime is shown to emerge with periodicity of several seconds. As the input power and laser wavelength are varied the temporal patterns change in period, duty cycle and shape. This dynamics is attributed to the multiple timescale competition between thermo-optical and thermo-optomechanical effects and closely resembles the relaxation oscillations states found in mathematical models of neuronal activity. We introduce a simplified model that reproduces all the experimental observations and allows us to explain them in terms of the properties of a 1D critical manifold which governs the slow evolution of the system.