Development of a laser vacuum gauge using a photothermal effect

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An Optical vacuum gauge is useful because of no electrodes inside vacuum systems. It is effective to measure the pressure for the space with very small amounts and to inspect the pressure of vacuum sealed devices. On the other hand, a photothermal effect is profitable for vibrating a membrane with no contact. In this investigation, the photothermal effect has been applied to the optical vacuum gauge. Following results have been obluained.1. It is cleared that the x)ressure in the low vacuum r-eyion (from 1 to 760 Torr) can be determined from the resonance frequency shift which depends on the 0'as density. Determinations by the resonance frequency is effective because of its accuracl and of its few affections from noises.2. Resonance frequency of the photothermal vibration shifted also in the medium vacuum rereion (from 1 to 10^<-3> Torr) since the temperature of the vibration, membrane increased with decreasing pressure. This is due to the pressure dependence of the thermal conductivity of ambient eases. It was cleared that the membrane having the larger thermal expdnsibn t coefficient showed the larver resonance frequency shift.3. Above methods are not effective for unknown composition eases. The rhotothermal vibration was applied to a diaphramm manometer, with which the space of unknown pressure and that of known pressure are divided. The resonance frequency shifts by the force caused from the differential pressure. The pressure from 10 to 10^<-3> torr could be determined.