Megamaser be very different from those that produce galactic water masers. Observations of water megamasers have been used to make accurate measurements of distances to galaxies in order to provide constraints on the Hubble constant. The word maser derives from the acronym MASER, which stands for "Microwave Amplification by Stimulated Emission of Radiation". The maser is a predecessor to lasers, which operate at optical wavelengths, and is named by the replacement of "microwave" with "light". Given a system of atoms or molecules, each with different energy states, an atom or molecule may absorb a photon and move to a higher energy
Sound amplification by stimulated emission of radiation operates at about 440 GHz, while the Caltech device operates in the megahertz range. According to a member of the Nottingham group, the two approaches are complementary and it should be possible to use one device or the other to create coherent phonons at any frequency in the megahertz to terahertz range. A significant result rises from the operating frequency of these devices. The differences between the two devices suggest that SASERs could be made to operate over a wide range of frequencies. Work on the SASER continues at the University of Nottingham, the "Lashkarev Institute of Semiconductor Physics" at