Laser Elsewhere, in the U.S., Schawlow and Townes had agreed to an open-resonator laser design – apparently unaware of Prokhorov's publications and Gould's unpublished laser work. At a conference in 1959, Gordon Gould published the term LASER in the paper "The LASER, Light Amplification by Stimulated Emission of Radiation". Gould's linguistic intention was using the "-aser" word particle as a suffix – to accurately denote the spectrum of the light emitted by the LASER device; thus x-rays: "xaser", ultraviolet: "uvaser", et cetera; none established itself as a discrete term, although "raser" was briefly popular for denoting radio-frequency-emitting devices. Gould's notes included
Sound amplification by stimulated emission of radiation tend to emit phonons randomly. Researchers have overcome the problem of terahertz frequencies by following various approaches. Scientists in Caltech have overcome this problem by assembling a pair of microscopic cavities that only permit specific frequencies of phonons to be emitted. This system can be also tuned to emit phonons of different frequencies by changing the relative separation of the microcavities. On the other hand, the group from the University of Nottingham took a different approach. They have built their device out of electrons moving through a series of structures known as quantum wells. Briefly, as an electron hops from