Measurement of high conversion efficiency to 123.6-nm radiation in a four-wave-mixing scheme enhanced by electromagnetically induced transparency

We report measurements of the absolute yield of 123.6-nm vacuum ultraviolet (VUV) radiation produced in a resonant four-wave-mixing scheme in krypton enhanced by electromagnetically induced transparency. One of the mixing fields, in the ultraviolet (UV) at 212.55 nm, was in two-photon resonance with the 4p(6) S-1(0)-4p(5)5p[0, 1/2] transition of krypton, while a second field (the coupling field) at 759 nm was resonant with the 4p(5)5p[0, 1/2]-4p(5)5s[1, 1/2] transition. Electromagnetically induced transparency has been predicted to be induced by this coupling field and to enhance the efficiency of the generation of the field at 123.6 nm, on the 4p(5)5s[1, 1/2] to 4p(6) S-1(0) transition. This was confirmed by measurements of the absolute VUV radiation yield using a calibrated photodiode in the limit of a large density-length product. Energies of similar to 30 nJ were produced. which gave a conversion efficiency, from the coupling field energy of similar to 1%. Higher yields are thought to be achievable by increasing the coupling laser. intensity, the path length of the medium, and by the use of a transform-limited UV pulse of the same duration as the coupling field.