Abstract

Coherent population trapping (CPT) has been widely investigated.^1,2 In the resonant interaction of two laser fields with three- energy-level systems, atoms can be trapped into the coherent superposition of the ground and excited levels, whereas the intermediate level remains unoccupied. Under these conditions the absorbing medium becomes transparent for powerful radiation. The interest in this phenomenon is due to its many applications. We show that trapped states are significant in the sum-frequency mixing of two arbitrary intense fundamental fields in three-level systems under both single- and two-photon resonances.

© 1995 Optical Society of America