Gabriel Popescu passed away in June 2022. He will be remembered as a creative leader in biophotonics, with pioneering contributions to quantitative phase imaging and spectroscopy, an engaging collaborator and a dear friend.
Gabriel (‘Gabi’) Popescu, a pillar of the biomedical optics and optical microscopy communities, passed away in an untimely manner in June, while visiting his hometown of Prundu in Romania. Professor Popescu had made major contributions to biomedical optics, microscopy and spectroscopy, and was considered to be a founder in the field of quantitative phase imaging. He was an inspiring and beloved figure, who was appreciated by many researchers.
Popescu was born in 1971 in Romania. He obtained his BS and MS degrees in Physics in 1995 and 1996, respectively, from the University of Bucharest, Romania. After moving to the US, he obtained his MS and PhD in Optics, in 1999 and 2002, respectively, from the School of Optics/CREOL, University of Central Florida. He then joined the G. R. Harrison Spectroscopy Laboratory at MIT, as a Postdoctoral Researcher under the direction of Professor Michael S. Feld.
In 2007, Popescu joined the University of Illinois Urbana-Champaign (UIUC) as an Assistant Professor, where he established the Quantitative Light Imaging (QLI) Laboratory. At UIUC, he held academic appointments in both the Electrical and Computer Engineering and Bioengineering departments. Until his last days, Popescu was William L. Everitt Distinguished Professor in Electrical and Computer Engineering at UIUC, and a Faculty Member at the Beckman Institute for Advanced Science and Technology.
Popescu’s research largely focused on label-free optical imaging using quantitative phase contrast1. His work transformed phase imaging, a non-destructive biomedical optical imaging method, into a quantitative tool. This label-free approach requires no exogenous labelling agents, ensuring maximum viability of biological samples and enabling quantitative cellular assays.
Popescu’s invention of diffraction phase microscopy (DPM), published in a seminal and highly cited paper in 20062, opened new avenues for robust interferometric quantitative phase imaging3. The DPM detection module can be readily added to existing microscopy systems to provide quantitative phase contrast. Importantly, this approach features a stable and robust interferometer design, ensuring significantly higher signal-to-noise ratio in comparison with conventional interferometric imaging systems. Today, DPM has been adopted by numerous laboratories worldwide and found various applications in biological research laboratories.
In 2010, Popescu presented the idea of spatial light interference microscopy (SLIM)4. Revisiting the concept of phase microscopy with a spatial light modulator, quantitative phase imaging of biological cells was enabled under white-light illumination. Using this method, the spatial noise level was greatly reduced compared with other coherent interferometric imaging approaches, enabling detection of sub-nanometre-scale phenomena in biological cells. SLIM-based tomography was introduced later5, enabling three-dimensional label-free imaging with axial optical sectioning in biological cells.
In 2017, Popescu introduced gradient light interference microscopy6, which enabled three-dimensional white-light quantitative phase imaging of thicker biological specimens, such as embryos.
Popescu also identified impactful biomedical applications of quantitative phase imaging, such as studying the physiology and diseases related to red blood cells7, neurons, animal sperm and tissue slices, as well as cell-growth dynamics and viability conditions. He demonstrated that quantitative phase imaging can be used for measuring cell mass changes with high sensitivity, formulating an important biophysical tool for studying cellular growth-cycle regulation. For both cells and tissues, Popescu formulated various useful biophysical parameters that can be extracted from quantitative phase imaging. Recently, he developed deep-learning approaches in quantitative phase imaging settings to achieve computational specificity without chemical labelling8.
In 2011 and 2010, respectively, Popescu wrote a landmark textbook entitled Quantitative Phase Imaging of Cells and Tissues9 and edited another book on Nanobiophotonics10. In 2014, he co-founded (and has since co-chaired) the Quantitative Phase Imaging annual conference at SPIE Photonics West, San Francisco, California, USA, which has become one of the largest conferences at this major international meeting.
Popescu served as an Associate Editor of Optics Express and Biomedical Optics Express, as well as an Editorial Board Member for Journal of Biomedical Optics and Scientific Reports. In 2012, he founded a start-up company, Phi Optics, to commercialize the quantitative phase imaging technologies developed in his lab.
Popescu authored more than 200 journal publications, more than 230 conference presentations, and more than 30 patents. As an internationally renowned scientist, he gave more than 240 invited and keynote lectures. He currently has an h-index of 70, with almost 20,000 citations (Google Scholar). He was a Fellow of OPTICA (previously OSA), SPIE and AIMBE. Notably, in 2022, he received the prestigious Dennis Gabor Award in Diffractive Optics from SPIE.
Popescu’s future research plans were to reformulate the definition of super-resolution imaging, develop deep-learning approaches for quantitative phase microscopy and tomography, as well as combine quantitative phase microscopy and other label-free imaging approaches for specific biomedical applications. There is no doubt that even greater innovative contributions would have come from Popescu’s laboratory if he would have remained with us.
In addition to his great scientific contributions, Gabi was widely known for living his best life. His friends appreciated his unique sense of humour, adventurous spirit and kindness. He touched the lives of many, not just through his research and teaching, but also by being a friend and colleague that all enjoyed meeting up with. He was always ready to discuss the science you were working on and his feedback was always encouraging, especially for the younger generations of scientists. Some of us had made plans to meet up with him again soon, and as with any untimely loss, it is heartbreaking to know that we will not get that chance.
Gabi is survived by his wife Catherine Best-Popescu, who is a Research Assistant Professor at UIUC, his daughter Sophia Popescu, 15, his son Sorin Popescu, 13, and his mother, Maria Popescu.
Gabi was a distinguished researcher, mentor, educator and great friend. He was a true leader and an inspiration to many colleagues and students in the optical and biomedical engineering communities. He will be deeply missed.
Park, Y. K., Depeursinge, C. & Popescu, G. Nat. Photon. 12, 578–589 (2018).
Popescu, G., Ikeda, T., Dasari, R. R. & Feld, M. S. Opt. Lett. 31, 775–777 (2006).
Bhaduri, B. et al. Adv. Opt. Photon. 6, 57–119 (2014).
Wang, Z. et al. Opt. Express 19, 1016–1026 (2011).
Kim, T. et al. Nat. Photon. 8, 256–263 (2014).
Nguyen, T. H., Kandel, M. E., Rubessa, M., Wheeler, M. B. & Popescu, G. Nat. Commun. 8, 210 (2017).
Park, Y. K. et al. Proc. Natl Acad. Sci. USA 107, 1289–1294 (2010).
Kandel, M. E. et al. Nat. Commun. 11, 6256 (2020).
Popescu, G. Quantitative Phase Imaging of Cells and Tissues (McGraw-Hill, 2011).
Popescu, G. (ed.) Nanobiophotonics (McGraw-Hill, 2010).
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Shaked, N.T., Park, Y., Boppart, S.A. et al. In memory of Gabriel Popescu. Nat. Photon. 16, 609–610 (2022). https://doi.org/10.1038/s41566-022-01056-1