Efficient sum-frequency mixing through transparency induced by autoionization

It is shown that efficient sum-frequency mixing is possible through transparency induced by autoionization. Tuning the incident laser frequencies to the absorption minimum of an autoionizing resonance for the generated wave greatly reduces the linear absorption of the generated wave while third-order susceptibility is still enhanced. The proposed scheme does not require any strong radiative couplings and would be particularly useful for the generation of short-wavelength radiation.