Large enhancement of fully resonant sum-frequency generation through quantum control via continuum states

A theory of quantum control of short-wavelength sum-frequency generation, which employs the continuum states, is developed. The proposed scheme employs all-resonant coupling and trade-off optimization of the accompanying constructive and destructive quantum interference effects in the lower-order and higher-order polarizations controlled by the overlap of two autoionizinglike laser-induced continuum structures. The scheme does not rely on adiabatic passage, coherent population trapping or maximum atomic coherence as a means to facilitate maximum output. The opportunities for manipulating transparency of the medium and refractive index for the fundamental and generated radiations, as well as nonlinear polarization in the multiple-resonant medium, are shown. This opens the feasibility of creating frequency-tunable narrowband filters, polarization rotators, and dispersive elements for vacuum ultraviolet radiation. The features specific for quantum interference in Doppler-broadened media are investigated. The feasibility of almost complete conversion of long-wavelength fundamental radiation into generated short-wavelength radiation, and of a dramatic decrease in the intensity of required fundamental radiations, is shown.