4Pi confocal optical system with phase conjugation

We propose a 4Pi confocal system that incorporates a phase-conjugate mirror into the system to solve the alignment problem and automatically correct the spherical aberration associated with the conventional 4Pi confocal system when observing a thick sample. The proposed system is experimentally verified by use of cerium-doped barium titanate crystal as the phase-conjugate mirror. The full width of the central peak is similar to 0.15 mu m. We also theoretically verify the advantage of automatic correction of the spherical aberration by calculating the intensity distribution at the focal spot. (C) 1996 Optical Society of America