The generic way to create them is to excite electrons into a metastable state, from which an avalanche process known as population inversion is triggered to the ground state.
One technique for achieving a high power output from these devices maintains a low quality factor initially, and then modulates it to a higher value; that technique is Q-switching. One variety based around sapphire doped with titanium is made tunable by inserting of an adjustable filter into the resonant cavity. Another type can be made from a cavity in which the magnetic field varies periodically through space called an undulator; in that type of this instrument, free electrons oscillating in the undulator radiate coherently. The generic way to create them is to excite electrons into a metastable state, from which an avalanche process known as population inversion is triggered to the ground state. For 10 points, name these devices which stimulate quantum transitions between levels to produce a focused beam of light.
One technique for achieving a high power output from these devices maintains a low quality factor initially, and then modulates it to a higher value; that technique is Q-switching.
lasers [or Light Amplification through Stimulation of Emitted Radiation]