Research Engineer / Postdoc at the Langevin Institute

Development of a Fiber-Based Probe for Real-Time Acousto-Optic Imaging

We are recruiting a Research Engineer or Postdoctoral Researcher (funded, 12–18 months) to develop an integrated probe combining optical fibers and ultrasound for real-time acousto-optic imaging, within the CNRS maturation project SONARIS. The goal is to move a lab-based system toward a clinical pre-prototype, with potential applications in non-invasive, non-ionizing breast cancer diagnosis. Join us in Paris!

Keywords: acousto-optic imaging, optical fibers, ultrasound, biomedical imaging, instrumentation, prototyping

The work spans probe design (optical fibers, laser illumination, ultrasound), mechanical CAD modeling, photonic crystal fiber integration, experimental optics/acoustics on phantoms, and data acquisition and image reconstruction.

TL;DR: We will build an integrated fiber-and-ultrasound probe to push acousto-optic imaging from the lab toward clinically relevant environments. Note: as the project's main objective is IP generation, it may not immediately lead to publications.

Supervision: Maïmouna Bocoum, Sébastien Popoff, François Ramaz (Institut Langevin / ESPCI Paris), and Jean-Michel Tualle (Laboratoire de Physique des Lasers).

Contact: Maïmouna Bocoum — maimouna.bocoum(at)espci.fr or François Ramaz — francois.ramaz(at)espci.fr

More information here.

Test of the new Vialux DMD mount for holographic applications

Antoine Loquet and Sébastien M. Popoff  

In a previous tutorial, we discussed mechanical instabilities in holographic setups when using a Vialux DMD. The main issues where the lack of dedicated mount and the fact that the DMD board is connected to the PCB by a rigid flat cable, allowing 1/ applying a small torque on the DMD when handling the board, and 2/ transmitting vibrations originating from the PCB fan to the DMD. Recently, Vialux released a dedicated mount for their DMDs. In this report, we present a comparative analysis of different mounts strategies when using a DMD in a holographic setup, including the new Vialux mount and homemade solutions with and without foam damping.

How to Correct for Bias in Off-Axis Holography for Transmission Matrix Measurements

Sébastien M Popoff¹ , Antoine Loquet¹

I presented in a previous tutorial how to reconstruct a complex field using a camera and a plane wave reference tilted with respect to the optical axis, known as off-axis holography. This works perfectly with an ideal plane wave as a reference. Of course, real life is not perfect, and the reference usually presents imperfections. While low spatial fluctuations can be compensated for afterward, high spatial frequency noise has the effect of adding a small bias to the estimation of the field. Such bias is typically small, but in transmission matrix measurements—since it is static and added to all measurements—it can affect the singular value distribution and perturb or hide transmission channels that would otherwise be visible.

ZoomFFT for speeding up off-axis computation (and more)

Sébastien M Popoff¹  and Rodrigo Gutiérrez-Cuevas¹

When performing the computation for some tasks such as off-axis holography, we often have to compute the entire FFT of a signal or an image while being only interested in a very small part of the spectrum. The rest of the information is just discarded. While the FFT algorithm and its implementation in standard computing libraries are very efficient, we can still take advantage of a slower approach which only computes what we need. The ZoomFFT algorithm does just that! And it's already available in standard packages such as SciPy for Python or in MATLAB. Using off-axis holography as an example, I will show how to save time – or not – using ZoomFFT.