Possibility and current status of absolute XHV measurement by laser ionization

S. Ichimura*, K. Kokubun, H. Shimizu, S. Sekine

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)


The current status and possibility of XHV measurement by laser ionization using second harmonics of a picosecond YAG laser are discussed. Under the condition that incident laser energy was 30 mJ/pulse and the laser beam was focused with a spherical lens (focal length f= 250mm) to a power density sufficient for the saturation Of H2 ionization at the focal point, the minimum pressure in an XHV chamber was measured. From the minimum pressure estimated by extrapolation (5 × 10-11 Pa) and the ion counting rate at that pressure (one count during 500 laser shots), the volume of the ionization region was expected to be 1.7 × 10-4 mm3. The ionization region was then measured experimentally under the same laser beam conditions. It was found that the ionization region has a spindle shape with maximum diameter of 45 μm and the length of 1.2mm. The estimated volume is larger than the expected volume by a factor between 4 and 12. The ion detection efficiency of the electron multiplier is one of the major factors affecting the difference, and it can be reduced to within a factor of 3. On the basis of the results, the possibility of absolute measurement of XHV pressure by laser ionization is discussed.

Original languageEnglish
Pages (from-to)545-552
Number of pages8
Issue number6-8
Publication statusPublished - 1996 Jan 1
Externally publishedYes


  • Ionization volume
  • Laser ionization
  • Molecular density imaging
  • XHV

ASJC Scopus subject areas

  • Instrumentation
  • Condensed Matter Physics
  • Surfaces, Coatings and Films


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