Coherent superpositions are created in our experiments by using resonantly tuned laser fields. We are actively engaged in developing robust sources of transform limited pulses using injection seeded pulsed OPO's for this and other purposes. With these lasers we can perform non-linear frequency mixing in dense atomic gases that results in the generation of a new field at a short wavelength. We use, however, a resonant laser field that coherently prepares the atoms in the sample. Interference between the quantum mechanical pathways controlling absorption and non-linear coupling processes can now occur in the atom.
Further work is now underway in which a large magnitude coherence is excited in the system.
This is done by using adiabatic excitation with two strong transform limited fields. In this condition frequency mixing with further laser fields can result in extremely high conversion efficiencies, effectively approaching unity. Our project aims to prove this technique in frequency mixing into the wavelength range below 160nm. An important technical aspect of our programme is that we are examining the effectiveness of frequency mixing via the atomic continuum states of a coherently prepared system. Presently there are two PhD students working on this project and we will be joined by an EU funded postdoctoral researcher in January 2001.