Gabriel Popescu, the William L. Everitt Distinguished Professor in Electrical and Computer Engineering in the University of Illinois Urbana-Champaign Grainger College of Engineering, died June 16. Popescu established and directed the Quantitative Light Imaging Laboratory at the university’s Beckman Institute for Advanced Science and Technology. His contributions to the field of biomedical imaging focused on transforming biomedicine into a quantitative science through advancements and innovations in optic science and label-free microscopy. He enabled quantitative measurements of the phase of light to pass through biological structures, providing previously inaccessible biological information without using dyes or stains that would perturb the dynamic biological processes the researcher is trying to measure. An internationally recognized researcher and thought leader in optics and biophotonics, Popescu authored the textbook Quantitative Phase Imaging of Cells and Tissues in 2011, published 185 journal publications, delivered 230 conference presentations, was issued 32 patents, and gave 220 invited talks. He also co-founded and chaired a conference at SPIE Photonics West that attracts more than 100 papers per year and has grown to be one of the largest at the event. “Gabi was leading a revolution in microscopy, using quantitative phase as a vehicle to enable a transformation in microscopy to be label-free and nonperturbative,” said Rohit Bhargava, Founder Professor of Bioengineering at the Grainger College of Engineering. “His work has led to greater understanding of image formation [and] of rapid measurements and quantitative microscopy.” Popescu's work enabled new understanding and applications in cellular and multicellular processes ranging from cancer-drug interactions to neuronal transport, Bhargava said. In addition to his R&D pursuits, Popescu served as founder and president of quantitative phase imaging technology company Phi Optics Inc. “I’m still in shock because he sat just down the hall from me and we shared many passions and interests,” said professor Stephen Boppart, head of the Biophotonics Imaging Laboratory in the university’s Beckman Institute. “He was a true visionary in the field of biophotonics and had a real talent for bringing people together and building collaborations around the world.” “This is such a terrible and tragic loss,” said Bruce Tromberg, director of the National Institute of Biomedical Imaging and Bioengineering at the National Institutes for Health (NIH). “Gabi brought people together with a brilliant technical vision and adventuresome spirit; he was an inspiration and truly a ‘bright light’ of our biophotonics community.” Gabriel Popescu. Courtesy of the University of Illinois Urbana-Champaign Grainger College of Engineering. Popescu served as an associate editor of Optics Express and Biomedical Optics Express and an editorial board member for the Journal of Biomedical Optics and Scientific Reports. He was also a reviewer at NIH and the National Science Foundation. Popescu was a fellow of SPIE, the international society of optics and photonics; Optica; and AIMBE (American Institute for Medical and Biological Engineering). He was a senior member of IEEE (Institute of Electrical and Electronics Engineers). He received the 2022 SPIE Dennis Gabor Award in Diffractive Optics.