Gravity laser
A gravity laser, also sometimes referred to as a Gaser, Graser, or Glaser, is a hypothetical device for stimulated emission of coherent gravitational radiation or gravitons, much in the same way that a standard laser produces coherent electromagnetic radiation. Principle of function. While photons exist as excitations of a vector potential and so contain an oscillating dipole term, gravitons are a spin-2 field and so have an oscillating quadrupole term. For efficient lasing to occur, there are several conditions that must be met: Alternate design proposals involve free undulators akin to a free-electron laser. Several proposals involve  exploiting the momentum transport properties of superconductors, where s-waves and d-waves couple distinctly to gravitational radiation. As of 2019, there are no plans to construct a gravity laser. Use in science fiction. The idea of gravity lasers has been popularized by science fiction works such as David Brin's "Earth" (1990). While attempting to remove micro singularities inadvertently introduced into the planetary mantle, it is found they can serve as mirrors. With the necessary energy levels found in gravitational potentials of the planet’s core and mantle, the resulting 'graser' beams are initially employed to nudge the singularities  somewhere safer. Other uses are soon found, such as propelling objects into space and for weaponry of various levels of sophistication. Other works, such as the RPG Star Ocean (1996) use them as a hypothetical weapon. They are also commonly employed as a proposed mechanism for tractor beams, antigravity, and space propulsion. Earth Unaware (2012) uses 'glasers' as a plot device to enable planetary-scale manipulation of matter, akin to gravity guns.