We use the four-wave difference frequency mixing of a nanosecond laser (UV) and a picosecond laser (visible) in xenon gas to generate a picosecond VUV laser radiation. Since the visible laser has a spectral range between 450 nm and 800 nm, we can obtain a tunable VUV laser, from 148 nm to 173 nm. The time duration of the pulses generated depends (linearly in our case) on the shortest laser, which is the picosecond laser.