Jerome Wenger NanoBioPhotonics

Plasmonic nano-optical trapping has revolutionized the use of optical tweezers, and a lot of attention has been devoted to the optical gradient force. However, the metal absorbs part of the incident light, leading to a temperature gradient responsible for an additional thermophoretic force which remains largely overlooked in plasmonic trapping.

In a recent Nano Letters publication, we experimentally disentangle the thermophoretic force contribution from the optical gradient force in double-nanohole plasmonic trapping. Our approach uses different surfactants which allow to tune the thermophilic or thermophobic response of the nanoparticles and set the relative strength of the thermophoretic force. This uniquely demonstrates that the choice of the surfactant can play a determining role in the outcome of the plasmonic trapping experiment.

Significance:

- Our method to measure separately the thermal and the optical forces is very general and can be easily extended to other plasmonic designs.

- The nano-optical trap performance can be significantly improved by properly choosing the surfactant to take advantage of the thermophoretic force.

Also freely available on Arxiv 2011.10263

After a 3-year endeavour, Aleksandr Barulin defended his PhD on Dec 4th 2020.

Thesis committee:

- Thomas Ebbesen, ISIS, Université de Strasbourg, France, President

- Niek van Hulst, ICFO-Institut de Ciences Fotoniques, Spain, Reviewer

- Christian Eggeling, Friedrich-Schiller-Universität Jena, Germany, Reviewer

- Hervé Rigneault, Institut Fresnel, France, Examiner

- Aude Lereu, Institut Fresnel, France, Examiner

- Jérôme Wenger, Institut Fresnel, France, Supervisor

Read the thesis abstract here.

The ability to design light concentrators directly integrated on a chip is an issue in many applications of optics. Published recently in APL Photonics, we have developed a CMOS compatible metasurface lens based on the index profiles derived from the Maxwell fish-eye distribution. Based on this rational physics-driven design, we fabricate and characterize the optical performance of the metalens, achieving tight submicron focusing in excellent agreement with numerical simulations.

An important point to note is that the design which is not based on resonant elements allows a large spectral bandwidth to be obtained. It is scalable, can be readily implemented and is robust to minor fabrication deficiencies.

Now published in Photoniques, the journal of the French Optical Society, international (english) edition: Is there a bright spot in the shadow of an opaque disk? Nearly 200 years ago, Augustin Fresnel and François Arago’s remarkable answer to this question validated the wave theory of light and inaugurated the modern theories of diffraction. Today, their renowned experiment can be easily reproduced using lasers and cameras. Far beyond its historical interest, the experiment is a versatile platform to illustrate the main concepts of optical physics, including diffraction, interference, speckle, and Fourier optics.

See also our series of videos on the youtube channel of Institut Fresnel.

Since October, we welcome Prithu Roy as new PhD applicant in our group. Looking forward to exploring the nanoworld in UV!