Abstract

Enhancement of third-harmonic generation near four-photon resonance showed¹ new possibilities for direct upconversion of visible or infrared light into VUV light. However, the observed efficiencies of the four-photon resonant six-wave mixing were low. Our theoretical analysis² showed that the efficiency is limited because of a destructive interference between the two-photon resonant Raman process E₂E₃ and the four- photon resonant excitation ${\text{E}}_1^4$ as shown in Fig. 1(a).

© 1994 Optical Society of America