Density dependent effects due to residual susceptibilities in a four-wave mixing scheme with electromagnetically induced transparency

摘要

We have studied the generation of vacuum ultraviolet radiation (at 123.6 nm) produced in a resonant four-wave-mixing scheme in krypton, enhanced by electromagnetically induced transparency. The interplay between the non-linear susceptibility (governing the wave-mixing), the linear susceptibility (governing the absorption and dispersion), and the density-length product was examined both experimentally and numerically. We observe favourable scaling of the yield with density-length product (NL) up to a value of 5×10~(16) cm~(-2). Above this NL value the yield decreases due to the background wave-vector mismatch (△k_(resid)), which arises from the additional atomic energy levels outside the three considered in the EIT enhanced mixing scheme. Our results suggest that further enhancements in frequency up-conversion can be achieved by employing a buffer gas as a phase matching agent.