Production and Measurement of Ultrahigh Vacuum

Abstract

In recent years, developments in experimental techniques have made it possible to achieve and to measure pressures which are many orders of magnitude lower than were previously considered possible. Thus, while pressures in the range between 10⁻⁶ mm Hg and 10⁻⁸ mm Hg have for many years been called “high vacuum”, it is now possible to evacuate an enclosure at room temperature to a total pressure of less than 10⁻¹¹ mm Hg. Although this value of pressure corresponds to a particle density of only 10⁵ per cm³, it still does not appear to be an ultimate limit defined by the physical properties of the materials or the techniques used. Since the lower limit is not yet determined, it seems reasonable to define ultrahigh vacuum as the region of pressures below 10⁻⁸mm Hg.