AVS 65th International Symposium & Exhibition
    Vacuum Technology Division Tuesday Sessions
       Session VT-TuP

Paper VT-TuP7
Development of a Measurement System for Pressures in Vacuum Regions using an Optical Method

Tuesday, October 23, 2018, 6:30 pm, Room Hall B

Session: Vacuum Technology Division - Poster Session
Presenter: Yoshinori Takei, National Institute of Advanced Industrial Science and Technology (AIST), Japan
Authors: Y. Takei, National Institute of Advanced Industrial Science and Technology (AIST), Japan
K. Arai, National Institute of Advanced Industrial Science and Technology (AIST), Japan
H. Yoshida, National Institute of Advanced Industrial Science and Technology (AIST), Japan
Y. Bitou, National Institute of Advanced Industrial Science and Technology (AIST), Japan
S. Telada, National Institute of Advanced Industrial Science and Technology (AIST), Japan
T. Kobata, National Institute of Advanced Industrial Science and Technology (AIST), Japan
Correspondent: Click to Email
Future primary standards of pressure based on optical measurement are being developed in national metrology institutes (NMIs) [1]. Pressure is proportional to refractive index according to both the equation of state of gas and the Lorentz-Lorenz equation. Refractive index can be measured using an optical method based on frequency measurement. Therefore, pressure measurements with a small uncertainty and a wide-range can be achieved. The purpose of this study is developing a pressure measurement system using an optical method for pressure range from 1 Pa to 100 kPa.

A Fabry-Perot interferometer was used for measuring the refractive index of the fulfilled gas in a chamber. The chamber, whose volume was around 7.6 L, was evacuated by a turbo molecular pump and a diaphragm pump. The background pressure and the pressure increase rate after closing the valve were respectively 1×10-3 Pa and 2×10-8 Pa/s, which cause one of uncertainty factors in a low pressure measurement. Pure nitrogen gas was used to fulfill the chamber. The pressure in the chamber was stabilized using a pressure balance from 10 kPa to 100 kPa or by simple accumulating from 1 Pa to 10 kPa. A commercially available external-cavity laser diode (ECLD) was used as frequency-tunable laser light source in order to measure wide-range frequency. The laser frequency was locked to a resonant line of an optical resonator installed in the chamber using the Pound-Drever-Hall (PDH) method. The locked frequency was measured by a beat signal comparing with the reference laser. Aluminum was used as the chamber material to reduce the temperature distribution around the optical resonator. Temperatures of the chamber were measured using several calibrated platinum resistance thermometers and several thermistors. The developed system measured fluctuations in the atmospheric pressure. The evaluated linearity and its uncertainty between refractive index of nitrogen and pressure from 1 Pa to 100 kPa gas are presented.

[1] Jay H. Hendricks et al., ⅩⅩⅠ IMEKO,1574-1577, (2015).