The measurement of gas pressure in ultrahigh vacuum was carried out by detecting laser-generated photoelectrons. Xenon atoms filling a vacuum chamber were nonresonantly ionized by a picosecond laser pulse. The laser intensity dependence of the number of ions produced was measured, and almost all xenon atoms in a focal area were found to be ionized. The number of photoelectrons produced was also measured as a function of xenon pressure. The signal intensity was proportional to xenon pressure in the range from 10-2 to 10-7 Pa.
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