A sine squared factor in the denominator of the gain-saturation function for these devices causes "spatial
 hole burning" in the gain coefficient.
A sine squared factor in the denominator of the gain-saturation function for these devices causes "spatial
 hole burning" in the gain coefficient. That gain coefficient is equal to a threshold value in
 "continuous-wave oscillation" of these devices, in which the cavity photon number is constant. These
 devices make use of a deviation from thermal equilibrium in which there are more electrons in a higher
 energy level than a lower energy level, a phenomenon known as population inversion, though ones that
 work without population inversion do so using quantum coherence. For 10 points, name these devices that
 produce highly coherent light through stimulated emission of radiation.
A sine squared factor in the denominator of the gain-saturation function for these devices causes "spatial
 hole burning" in the gain coefficient.
{lasers} [or light {amplification} by stimulated emission of radiation before "{stimulated}"]