ABSTRACT
We may also observe that the 20 years between the 1930s and the 1950s were not lost insofar that an acquisition of knowledge took place which was later used in masers and lasers. Moreover, these eorts were directed towards problems which, although they intrinsically contained ideas basic to the making of stimulated emission devices, had, however, a completely dierent end in mind. Among the arguments then under consideration were studies on magnetic resonance and optical pumping. During the World War II, the main eorts were directed toward the production and detection of microwaves for radars. e technical problems which were solved, among others, were the development of high-power generators, called magnetrons, to produce the radar signal; the construction of sensitive crystal detectors to detect the echo; the development of electronic methods of distinguishing the echo over the background noise; and the perfection of narrow-band ampliers, lock-in detectors, and other noise-reducing circuits to increase the sensitivity of the radar system.
