Rolf Widerøe (born 11.07.1902) is a Norwegian physicist and engineer and a member of the Norwegian Academy of Science and Letters (1973). He was born in Oslo. In 1927 he received his doctorate at the Higher Technical School in Aachen, in 1928 — 32 he worked in Berlin, in 1933-45 in Oslo, in 1946 - 52 at Brown Boveri (Baden, Switzerland), from 1952 at CERN and from 1959 at the DESY laboratory.
His research was in the field of the physics and technology of accelerators and of dosimetry. In 1927 he proposed the linear resonance accelerator and the cyclic induction accelerator (published in 1928) (he had arrived at the idea of the induction accelerator as early as 1922). In 1928 he built the first version of a linear accelerator with two accelerating gaps and gave its theory. He studied the particular features of the motion of an electron in a cyclic induction accelerator. He established that an accelerated electron, acted on by an alternating magnetic flux with rotational symmetry, can move in a circle of constant radius, and he proposed the so-called “betatron condition”. He obtained (1925) an expression for the frequency of the stable oscillations of electrons about a fixed orbit.