The possibility of vacuum pressure measurement by ionizing gaseous atoms or molecules with laser radiation was studied. Xe ions were successfully detected after irradiation by a focused Xe-Cl excimer laser, indicating that non-resonant 4 photon ionization was realized with the present system. It was confirmed that Xe signal intensity, as measured by a quadrapole mass analyzer, changed in proportion to Xe gas pressure from 10-5Torr to 10-9Torr. Xe isotopes were also measured and the results correlated well with their natural abundance.
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