■ Label-free optical imaging with super-resolution and 3D tomographic reconstruction of light scattered around nanostructures and through complex media

  Print version of this article

Description of the PhD project

We have developed an off-axis holographic optical microscope coupled with a near-field scanning optical microscope (NSOM). Based on Fourier analysis of the interference pattern formed between light scattered by a nanostructured sample and a reference laser beam, and measured with a CCD camera, we can numerically reverse the propagation of the electromagnetic (EM) field towards the sample and calculate its amplitude and phase in any plane between the sample and the camera. We have recently demonstrated this method to perform a tomographic 3D reconstruction of the EM field produced by a NSOM aperture tip on a plasmonic sample [1].

We plan in this thesis to investigate complex disordered media by holographic microscopy, and to use such media to develop a novel wide field optical microscopy method capable to measure super-resolved images of nano-objects in one single shot. In contrast with fluorescence microscopy, the method is label-free, and will be applied at visible and mid-infrared wavelengths.

Our holographic imaging microscope combined with a NSOM should allow one to study coupled EM resonators with nanometer scale control of their relative position, or complex media involving multiple scattering events such as disordered granular materials and biological samples. We will measure the near-field transmission matrix of a complex medium, which relates linearly the input and output EM modes at subwavelength scales, and we will study how correlation in a disordered sample impacts the far-field radiation.

A complex medium made of subwavelength scatterers offers interesting possibilities to couple evanescent modes associated to high spatial frequencies to far-field radiation [2,3], and vice versa [4]. Based on this property, we will develop a novel imaging method allowing the observation of a nanostructured object using a complex medium as a metalens [2]. The imaging method should achieve subwavelength resolution by recording in one single shot a holographic image of the far field speckle transmitted through the object and the complex medium, once the transmission matrix of the latter is known.

We also plan to extend the 3D holographic image reconstruction method to infrared wavelengths. Optical lithography and bottom up self-assembling methods allow one to produce complex microstructured materials whose structuration is de facto subwavelength sized when illuminated with infrared radiation. The high control of the sample morphology at micron scales should allow one to explore novel EM properties, such as electromagnetic transparency or optimized radiative properties of dense disordered materials which exhibit specific spatial correlation properties [5].

[1] N. Rahbany et al., ACS Phot. 5 , 1539 (2018). DOI: 10.1021/acsphotonics.7b01611
[2] C. Park et al., Phys. Rev. Lett. 113, 113901 (2014). DOI: 10.1103/PhysRevLett.113.113901
[3] F. Lemoult et al., Waves Random & Complex Media 21, 614 (2011). DOI: 10.1080/17455030.2011.613954
[4] V. Parigi et al., Opt. Expr. 24, 7019 (2016). DOI: 10.1364/OE.24.007019
[5] O. Leseur et al., Optica, 3, 363 (2016). DOI: 10.1364/optica.3.000763


Nano-optics, Digital holographic Microscopy, Complex media, Super-resolution microscopy, Metalens, Wavefront control

Research unit

UMR7587 Langevin Institute

Description of the research Unit/subunit

The Institut Langevin is an excellence center specialized in Optics and Acoustics, which is ideally located in the center of Paris (https://www.institut-langevin.espci.fr/). It is part of the ESPCI Paris, which is a major institution of higher education in physics, chemistry, and biology, an internationally renowned research center in which several Nobel laureate have worked, and a fertile ground of innovation for industry (https://www.espci.fr/en/). The institute brings together world-class fundamental and applied research with an interdisciplinary mission. As an example of its dynamism, its members have obtained 37 patents and created 6 startups between 2013 and 2017.
Attracting exceptional scientist in the fields of waves and imaging, the Institut Langevin assembles a unique combination of expertise on wave manipulation, including acoustics, optics, and electromagnetic waves, from fundamental research to industrial applications. The Institut Langevin is structured in four research axes: waves in complex media, wave physics for medicine and biology, non-conventional imaging and sensing, and subwavelength physics. The research project of the PhD student to be hired directly interests several permanent staff researchers with strong expertise (both in experiments and theory) in nano-optics and wave propagations through complex media. The institute Langevin will be for him/her an exceptionally favorable environment for the accomplishment of the PhD project.

Name of the supervisor
Yannick De Wilde (yannick.dewilde (arobase) espci.fr)

3i Aspects of the proposal

The PhD project is directly connected with Photonics, but it also concerns tangentially Advanced materials and Nanotechnology. The core of the proposal is the development of advanced optical holographic methods from the visible to the mid-infrared range to achieve label-free optical imaging with unprecedented spatial resolution and sensitivity (inherent to interferometric detection), and to investigate the optical properties of single nano-objects and the propagation of electromagnetic waves through complex materials in which multiple scattering occurs. The methods will allow one to image at any wavelength biological samples (cells, tissues), nanomaterials and nanostructures (optical antennas), and to characterize novel materials with correlated disorder. ESPCI, which is a highly interdisciplinary research center (it gathers laboratories specialized in physics, chemistry, and biology), is the perfect place to develop the project as several laboratories will provide highly original samples which are not available anywhere else (synthetic materials produced by self-assembling methods, micro and nano-porous materials, biological tissues, etc.). For instance, some complex samples with correlated disorder will be designed for applications such as radiative cooling related to energy saving, or stealth technology related to defense. Others will be designed to achieve super-resolved optical microscopy imaging of biological cells. We will also study the electromagnetic response of optical nanoantennas designed by lithography to improve the performances of IR detectors and sources. The work of the PhD student in the project will thus be mainly focused on optics, but he/she will have the chance to interact with biologists, chemists, and materials scientists regarding the sample that he/she will investigate. We emphasize that the PhD supervisor, Dr. Yannick De Wilde, has ongoing collaborations with the French industrial group Saint-Gobain which is a major actor highly interested in energy saving applications, and with the aerospace agency ONERA, which develops high performance imaging and spectroscopy instruments, and infrared detectors. Besides our industrial partners, the project will also benefit from international collaborations like for instance with the University of Beirut in Lebanon, and CREOL, the College of Optics and Photonics at the University of Central Florida.

Expected Profile of the candidate

The candidate is required to possess a Master Degree in Physics, with an important component of optics and electromagnetism. Experience in nano-optics, and multiple scattering of electromagnetic waves will be favored. Well-developed experimental skills as well as good knowledge in simulations, data analysis, interfacing of scientific instruments will be important, as most of the work will deal with optical microscopy imaging with cameras, combined with the use of a scanning probe microscope. Knowledge in nanofabrication techniques (optical/electric lithography and other clean-room techniques for the fabrication of nanostructured samples), scanning probe microscopy, biology and materials science, will be welcome even though not mandatory. The PhD student will be integrated in a group of approximately ten people, including permanent staffs, PhDs and Postdocs. It is thus essential that he has excellent social skills.

Important dates

Call for applications : from July 16th to September 17th 2018
Eligibility check results : Late September
3i Committee evaluation results : Late October
Interviews from the shortlisted candidates with the Selection Committee : Mid-December (week of December 10th)
Final results : Late December

10 Rue Vauquelin, 75005 Paris