  A theoretical optimization method of high-harmonic-generation (HHG) is
developed in the framework of optimal-control-theory (OCT). The target of
optimization is the emission radiation of a particular frequency. The OCT
formulation includes restrictions on the frequency band of the driving pulse,
the permanent ionization probability and the total energy of the driving pulse.
The optimization task requires a highly accurate simulation of the dynamics.
Absorbing boundary conditions are employed, where a complex-absorbing-potential
is constructed by an optimization scheme for maximization of the absorption. A
new highly accurate propagation scheme is employed, which can address explicit
time dependence of the driving as well as a non-Hermitian Hamiltonian. The
optimization process is performed by a second-order gradient scheme. The method
is applied to a simple one-dimensional model system. The results demonstrate a
significant enhancement of selected harmonics, with minimized total energy of
the driving pulse and controlled permanent ionization probability. A successful
enhancement of an even harmonic emission is also demonstrated.
