Joseph Weber resigned from the Navy and entered graduate school at the Catholic University of Washington. Quantum mechanics was part of his studies and the idea of the maser came after attending a lecture on stimulated emission give by Karl Herzfeld. The principal characteristic of the maser is its extremely low noise, both as an amplifier and an oscillator. Townes understood immediately that one important application of molecular beam masers would be molecular spectroscopy. After the Strandberg seminar, Nicolaas Bloembergen asked him why he was thinking of a solid system that could not have the spectral purity of the ammonia maser. Unfortunately he and his group at Harvard were interested, for astronomical purposes, in a device working on the interstellar hydrogen line at 1420 MHz and therefore chose a material which could work at that frequency, failing to obtain the first successful operation of the three-level maser.