Returning to Stanford in 1945 as a full professor, he embarked on the construction of a series of linear accelerators based on klystron technology and of GeV performance. Along with the Varian brothers and Edward Ginzton, he co-founded Varian Associates in 1948. Sadly, he was never to see the completion of the klystron project. He died at age 39 in Palo Alto, California of berylliosis and fibrosis of the lungs, caused by inhaling the beryllium used in his research. In 1947, the Hansen Experimental Physics Laboratory (HEPL) was founded as a facility at Stanford University. The facility is designed to promote interdisciplinary enterprises across different branches of science and was named in his honor.