The measurement of the refractive index of air by interferometry
Length measurement by laser interferometry is becoming common practice in industry, the length being calculated from a formula involving the refractive index of the medium. Commercial interferometers provide automatic correction for variation in refractive index due to pressure, temperature and humidity, but the influence of CO(2) or other gases is neglected. For metrology work this is insufficiently accurate, and such laboratories have therefore constructed refractometers for the direct measurement of refractive index with accuracy better than 1.0 E-7. For the intercomparison of their measurements, the refractometers of the four participating laboratories were placed in a thermally controlled cabinet equipped with instruments to measure temperature, pressure, humidity and CO(2). There were many fluctuations between measurements which, in addition, did not always coincide with the calculated data. This may have been caused by very small variations in the atmosphere measured by the individual refractometers. In general, the results showed excellent agreement (5 x 1.0 E-8 or better) and confirmed the uncertainty estimates of the individual laboratories. A synthesis report is published with the same title, as EUR 10838.
Bibliographic Reference: EUR 13780 EN (1991) 17 pp., MF, ECU 4
Record Number: 199110950 / Last updated on: 1994-12-02
Original language: en
Available languages: en