Direct measurement of a VUV transition oscillator strength in xenon

A new method for accurately measuring the oscillator strengths of gases is presented. The technique is based on determining the phase-matching conditions for a laser four-wave mixing process in a gas mixture. By using high gas pressures, the measurement is independent of the detailed experimental geometry or spatial mode properties of the laser. Using the refractive index of argon as a reference, the oscillator strength of the xenon ground state to 7s[3/2]1 transition at 117.04 nm was found to be 0.098 +- 0.012. This value is more precise than previous results obtained from more complicated low-angle electron scattering experiments