What best describes the term 'metastable state' in relation to laser production?

The term 'metastable state' in the context of laser production refers to a long-lived energy state of an atom or molecule. When an atom is in a metastable state, it has absorbed energy and moved to a higher energy level, but does not immediately return to its ground state. Instead, it can remain in this excited state for a relatively extended period before transitioning back to the lower energy state.

This prolonged duration is essential for laser operation, as it allows for the accumulation of atoms in this excited state. When a sufficient number of atoms are in the metastable state, they can then participate in stimulated emission, which is the fundamental process that generates the coherent light characteristic of lasers. The fact that atoms can remain in this state for a longer time compared to more immediate excited states is what makes it crucial for efficient laser action.