ultravacuum

noun

1. A nearly perfect vacuum; i.e. an almost or fully complete absence of matter, especially a gas at very low pressure.

   “The operating principles employed in the thermal and ionization gauges are to be contrasted with the mercury manometer and Bourdon tube type vacuum gauges which have been used for years. The mechanics of these latter gauges seriously limit their use to the continuous measurement of high and ultravacuums.”

   “These lines are so-called “‘forbidden”’ lines which, in the crowded conditions even in a laboratory vacuum, would not appear; in the ultravacuum of a nebula, the atoms have no choice but to emit the forbidden energy.”

   “Some experiments which require the achievement of exceedingly antiseptic vacuum conditions have had to be preceded by intense research into the general problems of ultravacuums and surface physics. The problem of physical measurements on plasmas has required that many new instruments and techniques be developed.”

   “This behavior may be associated with chemical changes that are apparent in the composition of the gas phase as revealed by mass spectrometry techniques. Bursts of gas have been observed when a crystal is cleaved under ultravacuum conditions (117).”

   “Then there are problems of measuring what goes on in an ultravacuum. This gadget is a tensile stress-testing machine—operating on samples in an ultravacuum chamber.”