Sound amplification by stimulated emission of radiation vector in the second proposed scheme, is supposed to be determined by magnitude of in-plane magnetic field. Therefore, such kind of SASER is tunable (i.e. its wavelength of operation can be altered in a controlled manner). Common semiconductor lasers can be realised only in direct gap semiconductors. The reasoning behind that is that a pair of electron and hole near minima of their bands in an indirect gap semiconductor can recombine only with production of a phonon and a photon, due to energy and momentum conservation laws. This kind of process is weak in comparison with electron-hole recombination in a
Sound amplification by stimulated emission of radiation means that, since bosons with the same energy can occupy the same place in space, phonons and photons are force carrier particles and they have integer spins. There are more allowed states available for occupancy in a phonon field than in a photon field. Therefore, since the density of terminal states in the phonon field exceeds that in a photon field (by up to ~10), phonon emission is by far the more likely event. We could also imagine a concept where the excitation of an electron briefly leads to vibration of the lattice and thus to phonon generation. The vibration