Roy J. Glauber, Nobel laureate, passed away Dec. 26, 2018, at the age of 93. Glauber was awarded one-half of the 2005 Nobel Prize in Physics “for his contribution to the quantum theory of optical coherence.” Glauber’s prize-winning work centered on his development of a theory that advanced the understanding of light by describing the behavior of light particles. Presented in the early 1960s, the theory merged the field of optics with quantum physics and formed the basis for the development of quantum optics. Glauber received a Ph.D. in physics from Harvard University in 1949. After graduation, he did research at the Institute for Advanced Studies in Princeton, N.J., and at the California Institute of Technology. In 1952, he returned to Harvard. Glauber’s research helped clarify how light could have both wave and particle characteristics and explained the fundamental differences between the light emitted by hot objects, such as electric lightbulbs, and the light emitted by lasers. Practical applications of Glauber’s work included the development of highly secure codes in the field of quantum cryptography. Glauber was the Mallinckrodt Professor of Physics at Harvard University and Adjunct Professor of Optical Sciences at the University of Arizona. He was elected an OSA Fellow in 1985 and became an OSA Honorary Member in 2008 for his pioneering work on quantum optics and coherent states. Family members said he died at a hospital in Newton, Mass. The cause of death was acute respiratory failure, his son said.