The essential components of an adaptive optics system are a wavefront sensor for measuring aberrations, a device for correcting them, and feedback. Our current wavefront corrector is a continuous faceplate Xinetics deformable mirror with 97 PMN actuators that can independently push or pull to shape the mirror surface. This correction device is a miniature version of those used in telescope adaptive optics systems. In astronomical adaptive optics, light from a guide star is used to measure the aberrations of the atmosphere. Since there are no stars in the eye, an artificial light source must be used. We use a near infrared superluminescent diode (similar to a laser diode but with lower coherence) to form a point source on the retina. The reflected light from this point source is delivered to a wavefront sensor, and the eye's aberrations are calculated. A signal is then sent to the deformable mirror, which lies in a plane conjugate to the eye's pupil, telling it what shape it must assume to compensate for the aberration. This iterative procedure results in a nearly planar wavefront. The whole process takes place in only a fraction of a second.

Below is an illustration of the basic principle of adaptive optics and a photo of the deformable mirror. A point source of light from the retina emerges as an aberrated wavefront and propagates to the deformable mirror. The mirror, which is 75 mm (3 in) in diameter, corrects the aberrated wavefront to produce a planar wavefront that can be imaged by a lens to a sharp point on a science camera.

A more detailed diagram of our adaptive optics system: (Additional information for this system can be found on the 2nd generation AO system page

These before and after pictures of the wave aberration and point spread function (PSF) for one subject show how well the adaptive optics system can correct the eye's aberrations. The top left picture shows this subject's wave aberration when defocus and astigmatism (or sphere and cylinder, as with glasses or contacts) are corrected. This wave aberration still has several peaks and valleys, indicated by the high density of contour lines, due to the presence of other higher order aberrations and yields a very distorted image of a point of light (PSF) for this subject. The wave aberration after correction is illustrated in the top rightmost figure and its associated PSF is depicted in the bottom rightmost figure. The compensated wavefront is nearly perfectly flat and yields a tighter, more compact PSF. The wave aberration and PSF were measured and computed over a 6.8 mm pupil size.

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