Broadly tunable vacuum-ultraviolet radiation source employing resonant enhanced sum–difference frequency mixing in krypton

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Abstract
Vacuum-ultraviolet (VUV) generation by resonant third-order sum–difference frequency conversion (wVUV = 2wR − wT) in krypton has been investigated. The frequency wR (λR = 212.55 nm) was resonant with the Kr two-photon transition 4p–5p[1/2, 0]. By tuning wT in the range λT = 220–860 nm it was possible to generate wVUV in the wavelength range λVUV = 200–120 nm. The conversion efficiency was enhanced in the range 121–123 nm by phase matching with a normally dispersive buffer gas (Ar); under the best phase-matched conditions employed, VUV output powers at the Lyman-α wavelength of the order of 1 kW were inferred from the estimated VUV pulse energy. This source was used to measure high-lying members of the Mg principal series near 162 nm. High resolution and excellent sensitivity of detection, when a thermionic diode detector was used, have been demonstrated.