Development of a standard vacuum gauge and a pressure sensor in the medium vacuum region using laser Rayleigh scattering

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The feasibility of employing laser Rayleigh scattering as a standard vacuum gauge and a pressure sensor in the medium vacuum region (10^<-2>-1 Torr) was investigated.For the investigation of the standard gauge, a high sensitivity diaphragm gauge was used as a reference gauge. The rayleigh scattering signals showed a linear correlation with pressure values measured by the diaphragm gauge with a deviation of <5 % for the pressure region of >10^<-2> Torr. Standard deviations of Rayleigh scattering signals were in the range of 2-8 % for 10^<-2>-1 Torr, and these could be explained by an estimation based on photon statistics. In addition, it was shown that the absolute value of the pressure can be determined based on the atmospheric pressure and the Rayleigh scattering at this pressure.Two experiments were performed for the investigation of the pressure sensor. For the first experiment, a YLF laser pumped by a semiconductor laser (output 0.2 mJ in 7 ns, lambda=523 nm, repetition 1 kHz) was used as a light source and the beam was directed into a compact vacuum chamber. The stray light level was reduced to 20 m Torr, and the linear correlation between the Rayleigh scattering signal and the pressure value by the diaphragm gauge was obtained with an error of <7 % for 20 m Torr-1 Torr. These results showed that it is possible to make a compact pressure sensor using Rayleigh scattering.The second experiment was performed on a prototype pressure sensor. A cw semiconductor laser (output 500 m W, lambda=680 nm) was used as the light source and was modulated to give pulses with a 0.5 ms width. Rayleigh scattering signals were successfully detected down to 1 Torr with the error of <9 %. This measn that the sensor will be realized if the detection lower limit can be improved by a factor of 100.