Abstract

Atomic oscillator strengths of resonant transitions are important quantities, however experimental values of these parameters in VUV/XUV region are not accurately known and difficult to measure. The most important reason is that windowless environment is required for measurement of the intensities of the third harmonics (THG) or four-wave sum-mixing (FWSM), and neither the heat-pipe oven nor the gas cell technique works well, especially for the case of the gas mixture. In this paper we report a windowless, geometry-independent method for measuring the relative oscillator strength of gases in VUV/XUV region by observing phase matching in the FWSM and THG processes using a gas jet. Comparing with previous methods, our method has the following characteristics. The pulsed gas jet was first used in the experiment, thus a windowless environment is provided and it is possible to measure the oscillator strengths below 104.5 nm. The results of measurement are independent of any knowledge of fundamental beams, the gas distribution and the focal conditions, thus the accuracy of the measurement is improved; The fundamental beams are focused, thus the wave-mixing process near the level with small oscillator strengths is enhanced and small value of the oscillator strength can be measured.

© 1996 Optical Society of America