Logan E. Hargrove, a longtime supporter of acoustics, especially physical acoustics, performed his own important research and also had a wide impact in the scientific careers of others and the Acoustical Society of America (ASA). He passed away on February 18, 2019.
After receiving his PhD in physics from Michigan State University (East Lansing) in 1961, the first stage in Logan’s career was at Bell Laboratories, where he invented the mode-locked laser. Much like the acoustic longitudinal modes of a long pipe, the longitudinal optical modes of a long laser cavity are nearly harmonically spaced, with a frequency spacing equal to the inverse of the round-trip time of light along the cavity. A tube of energi