Vacuum ultraviolet 178.7 nm emission in sodium vapour under two-photon resonance excitation

T. S. Yih, B. J. Pong, W. T. Cheng, C. C. Chu

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


We have observed a fixed wavelength emission at 178.7 nm in sodium vapour under 578.7 nm two-photon resonance excitation. The proposed non-linear wave mixing scheme is described by ω178.7 nm = 2ωL + ω465.7 nm; where ω178.7 nm is the 178.7 nm photon frequency, ωL is the laser-photon frequency, and ω465.7 nm is the 465.7 nm photon frequency. This 465.7 nm emission comes from another six-wave mixing process involving two hyper-electronic Raman scattering photons. The excitation spectrum of the 178.7 nm emission has a typical multiwave mixing pattern with a competing effect appearing at higher temperatures under two-photon resonance excitation. Numerical analysis indicates that this vacuum ultraviolet emission has a poor phase-match condition that will depress the emission intensity to a certain extent. This makes the observation more difficult compared with other reported four-wave mixing generated emissions. Fortunately, on the one hand, it is enhanced by quasi-auto-ionization resonance when the 3s-5s transition is coupled to the sodium continuum by a 330.2 nm photon. On the other hand, its wavelength sits so close to the sodium Cooper minimum that weak absorption will not suppress this vacuum ultraviolet emission further.

Original languageEnglish
Pages (from-to)1463-1476
Number of pages14
JournalOptical and Quantum Electronics
Issue number10
StatePublished - 1996


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