Master thesis position: Bridging optical trapping and dielectrophoresis, across the terahertz gap

2018 Physics Nobel Prize has been awarded to A. Ashkin « for the optical tweezers and their application to biological systems. OT’s have now become indispensable in the biophysicists’ toolkit. It allows label free experiments on single cells leading to several breakthroughs in biology such as measuring the force of flagella of a bacteria or understanding DNA structure or RNA transcription by grafting them to a µ-bead. However, the investigation of systems at smaller scales is hindered by optical diffraction that limits the focusing and the subsequent optical forces. For this reason, the extension of free space OT below 50 nm, at visible wavelengths, for a dielectric target and biology compliant power, is extremely difficult.

Figure: Left typical aimed metasurface , middle schematic of the cross section of the targeted sample, right THz optical setup

During this internship, we will propose a novel approach aiming at using longer wavelengths to rap smaller objects. Though it looks counterintuitive, in the Terahertz range, metals absorb 2 to 3 orders of magnitude less in the THz than in the visible or infrared ranges. Thus, they transduce light into heat 100 to 1000 time less giving rise to much weaker competitive forces and thus allow to use lasers that are more powerful. In this work, we will take the full benefit of these properties of metal to enable optical trapping in TeraHertz plasmonic metasurfaces where the photonic mode will be shrunk to few µm^3. The consequent huge gradient field will induce as huge optical force without the drawback of the thermal perturbation and thus better trapping. We aim at establishing a novel state of the art for optical trapping thanks to this approach.

The proposed work includes a simulation part where the student will design the trap. It will be followed by a fabrication part exploiting the µ and nano fabrication facilities at IEMN. Then, the main part will use the optical trapping set up to perform the experiment and evaluate quantitatively the trapping. A data analysis will follow.

The student will work with a team of experienced researchers in the THz-Photonics group at IEMN Laboratory ( The group has a long lasting experience in the conception and realization of THz optoelectronic devices, and is fully equipped to carry out this project. The Laboratory hosts a 1500m2 clean-room with state of the art growth and fabrication facilities. IEMN is located in Lille, the capital of French Flanders, a vibrant city close to the Belgian border at 50 min by train from Paris-CDG airport.
We are looking for a physics or engineering master student or equivalent. Having one of the following skills would greatly increase the chance of success of any application: Experimental optics – Electromagnetism – Photonic simulation – Micro-nano fabrication
The exact tasks in which the student will be involved will be discussed together with him/her and the team and will depend on its capacities and taste as the needs of the team. We strongly advise any potential candidate to contact us by email or elsewhere to begin the discussion before any formal application.

Key words: TeraHertz, Optical Trapping, Plasmonics, Metasurfaces, Microfluidics

Possibility to go on with a PhD?
Yes, we are looking for two PhD student in the group next year one of them will have to deal with a really close subject.

Envisaged fellowship?
We already applied for several nationwide and European grants but the safest funding way will be to get a university of Lille grant. We are highly supported by the university and the chance of success are very high in this call for a good candidate.

Unité d’accueil :
Centre de Micro et Nano fabrication
Avenue Poincaré

Contact: Théo Hannotte / Dr Romain Peretti