Optimal control of strong-field phenomena

We discuss the possibilities of quantum optimal control theory (OCT) to enhance or suppress strong-field effects in atoms and molecules. We briefly review the basic principles of OCT and demonstrate how it can be used for various purposes by reformulating the target functional. Then we present different applications including controlled excitations, enhanced ionization, suppressed ionization, and -- in particular -- high-harmonic generation. The main focus is in single-electron systems, but examples and ongoing work in the multielectron regime, mainly in the framework of time-dependent density-functional theory, are mentioned as well.