Biological tissues are rarely transparent. That fact has long complicated efforts by optical microscopists to resolve deeply embedded features, because the light waves used for imaging are scattered throughout the intervening tissue. The deeper the object, the more blurred the image. To ameliorate the problem, scientists in recent years have turned to adaptive optics: Using rapid, real-time analysis of a distorted-light signal, a computer-controlled deformable mirror or spatial light modulator compensates for aberrations in the optical path by reshaping the waves and thereby restoring crisp image detail.
Conventionally, the deformable mirror is placed at the microscope’s so-called pupil plane—the back focal plane of the objective lens—where the mirror applies a uniform correction everywhere in the image plane. Such placement is appropriate, and provides the best focus, when the aberrations are spatially invariant, as is the case, for instance, when a refractive-index mismatch occurs along a flat interface. However, that condition...
