It is typically used to prevent unwanted feedback into an optical oscillator, such as a laser cavity.
When the coherent optical oscillator was first imagined in 1957, it was originally called the "optical maser."
The question, then, is what would CPA look like for an optical parametric oscillator?
In the optical parametric oscillator the initial idler and signal waves are taken from background waves, which are always present.
The most prominent ones were experiments with light fields using lasers and non-linear optics (see optical parametric oscillator).
A laser which produces light by itself is technically an optical oscillator rather than an optical amplifier as suggested by the acronym.
They are also used in optical parametric oscillators and some interferometers.
A device that is very close to my heart is called an optical parametric oscillator.
People who make optical parametric oscillators talk about back conversion, where the signal and idler start recombining to make more of the input laser beam.
In the case with the optical parametric oscillator, the energy returns to the original laser beam.