A lot of people use the terms deformable mirror and adaptive optics interchangeably - "Let's put adaptive optics in the beam." - with no regard for the fact that the singular form of the noun optics, - "the adaptive optic goes right before the beamsplitter" - is almost never used anymore. The trouble with the terminology is that there is no need for the confusion. Adaptive optics is a closed loop system; a deformable mirror is a special type of active mirror. Saying âThe active mirror goes right before the beamsplitterâ is okay â as long as it really doesn't go after the beamsplitter.
Another popular misconception is describing an adaptive optics system by referring only to the deformable mirror. âOh, you're going to add adaptive optics. How many actuators?â Actually, if the system was designed cleverly and only one type of aberration is going to be corrected, focus for instance, you might have a system with 2000 subapertures in the wavefront sensor, a special purpose microprocessor, a million dollar beamsplitter - but one actuator! (This system is not recommended by me; it is for satirical purposes only.)
A deformable mirror is one part of an adaptive optics system. Sometimes it is the most important part. Sometimes it is the most difficult part to build. Sometimes it is the most expensive part. But in any case, without something to control the deformations on the DM, it is a rather passive part.
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