Lofgren graduated from University of California Berkeley in May 1938, and got a summer job working on East. O. Lawrence"s new 37-inch cyclotron completed in 1937, at a salary of about $0.50 an hour.
He was an important figure in the breakthroughs that followed the creation of the Bevatron, of which he was the director for a time. At that time there was no government funding for scientific research, and the money came from medical foundations interested in evaluating the possible uses of neutron beams for cancer treatment and for producing radio-isotopes for medical research. In the fall of 1940 he was hired by Lawrence to help on adapting and using the 37-inch cyclotron to separate isotopes of uranium for the atomic bomb project
Later, he went to Los Alamos, where the first bombs were designed and built, and where he remained for the rest of the war.
With the end of the war he returned to Berkeley to complete the final year of his degree program, then went on to the University of Minnesota as a post doctoral fellowship He then returned to the laboratory at Berkeley and remained at the Laboratory until his retirement in 1982.
He turned 100 in January 2014.