Laser Photoionization Measurements of Pressure in Vacuum

For some time, laser photoionization has been used to detect low concentrations of atoms, molecules, and radical intermediates in a variety of applications, including analytical chemistry, combustion, plasma and CVD diagnostics. Several of these studies have shown that laser photoionization has the fundamental sensitivity and selectivity necessary for species-specific partial pressure measurement in the ultrahigh vacuum regime. This body of work has, in part, spurred interest in the application of laser photoionization to measurements of pressures in the UHV regime. In this paper we discuss the results of the recent research conducted at NIST on the use of laser photoionization for quantitative pressure measurements and the factors which limit the pressure measurements based upon this technique.