Mathieu Kociak is a senior research director at the French National Centre for Scientific Research (CNRS), working within the STEM group at the Laboratory for Solid State Physics (LPS) in Orsay, France. His research focuses on understanding the interplay between structure and the optical and electronic properties of individual nano-objects. To this end, he combines advanced instrumentation development in electron microscopy, experimental investigations using scanning transmission electron microscopy (STEM), and theoretical modeling of electron–matter–photon interactions.

His current work emphasizes nano-optics with fast electrons, employing techniques such as electron energy-loss spectroscopy (EELS), STEM-cathodoluminescence (STEM-CL), and more novel approaches like electron energy-gain spectroscopy (EEGS) and cathodoluminescence excitation spectroscopy. He has successfully transferred his STEM-CL technology to the company Attolight.

Since July 2021, he has led the STEM group at LPS. He is also the scientific coordinator of CHROMATEM, a flagship project dedicated to ultra-high energy resolution electron microscopy. In addition, he served as director—and then deputy director—of METSA, the French national network for advanced electron microscopy (2016-2025). He is advisor for core facilities and major Instruments at Université Paris-Saclay since January 2025.

Mathieu has organized or co-organized several major scientific events, including the EBEAM2022 and EBEAM2024 schools. He is the recipient of an ERC Advanced Grant (FreeQCC, 2025–2030). His work has been recognized with several honors, including the quadrennial FEI-EM Award (2012) from the European Microscopy Society, the Innovation Prize from Université Paris-Sud (2014), and the Agar Medal from the Royal Microscopical Society (2015).