In optics, tilt is a deviation in the direction a beam of light propagates.
Tilt quantifies the average slope in both the X and Y directions of a wavefront or phase profile across the pupil of an optical system.
Piston and tilt are not actually true optical aberrations, as they do not represent or model curvature in the wavefront.
Jitter can arise from three-dimensional mechanical vibration, and from rapidly varying 3D refraction in aerodynamic flowfields.
Jitter may be compensated in an adaptive optics system by using a flat mirror mounted on a dynamic two-axis mount that allows small, rapid, computer-controlled changes in the mirror X and Y angles.
A gimbaled optical pointing system cannot mechanically track an object or stabilize a projected laser beam to much better than several hundred microradians.
Light, however, has no appreciable momentum, and by reflecting from a computer-driven FSM, an image or laser beam can be stabilized to single microradians, or even a few hundred nanoradians.
This almost totally eliminates image blurring due to motion, and far-field laser beam jitter.