Both Wood and Pfund left Wisconsin for [[Johns Hopkins University]] in 1903. From 1903 to 1905 Pfund was a Carnegie research assistant and continued to work under Wood. In 1906 Pfund earned his Ph.D. in physics and was a Johnston scholar from 1907 to 1909. He remained at Hopkins for the remainder of his career, eventually becoming a full professor and later chair of the physics department. From 1943 to 1944 Pfund served as the president of the [[Optical Society of America]].
Within the [[hydrogen spectral series]] Pfund discovered the fifth series, where an electron jumps up from or drops down to the fifth fundamental level. This Series is known as the ''[[hydrogen spectral series#Series|Pfund series]]'', named for him. He also invented the ''[[Pfund telescope]]'', which is a method for achieving a fixed telescope focal point regardless of where the telescope line of sight is positioned, and the ''[[Pfund [[Astrocompass|sky compass]]'',<ref>[http://www.ion.org/publications/abstract.cfm?articleID=102101/ Moody, Lieutenant Commander Alton B., ''"THE PFUND SKY COMPASS",'' NAVIGATION, Journal of The Institute of Navigation, Vol. 2, No. 7, 1950]</ref> which arose from Pfund's studies of the polarization of scattered light from the sky in 1944, and which greatly helped [[Polar route|transpolar flights]] by allowing the determination of the Sun's direction in twilight.<ref>[http://www.osa-opn.org/home/articles/volume_21/issue_6/departments/the_history_of_osa/presidents_of_the_late_1940s/#.UWMZz6sY0i4 Presidents of the Late 1940s], John Howard, Optics and Photonics News, June 2010, last accessed 2013-04-08.</ref> Pfund is also noted for his work into the area of infrared gas analysis.
