Solid-state lasers where the whole LaserResonator consists only of one piece of crystal or glass.
Monolithic lasers according to a strict definition are when the whole Laser Resonator consists only of some piece of crystal or glass. The resonator is then closed either with Dielectric mirror coatings on the surfaces, or with total internal reflection. A somewhat relaxed definition allows for reflections from additional optical elements, and even for additional components within the laser resonator, as long as these elements are rigidly attached (e.g. bonded) to the Gain medium.