ABSTRACT
It has been suggested to correct for aberrations of the wavefront using adaptive optics, as is discussed in Chapters 4, 7 and 8 on adaptive correction. ”ere the idea is to feed a pre-aberrated wavefront to the optical system that contains aberrations opposite to those generated within the system. Hence, aberrations will cancel out and di§raction-limited imaging is accomplished again. A standard adaptive optics system includes a wavefront-sensing element and operates in a closed loop to correct aberration actively. Another approach is to use predictive aberration correction, sometimes referred to as open loop control. Here, the aberration conditions are inferred from secondary parameters-for example, the position of the focal spot within the specimen-and corrected accordingly. ”erefore, the simulation and prediction of aberrations is the key to predictive correction.
