Some measurements on refractive indices of gases in the microwave region

✍ Scribed by F.W. Heineken; F. Bruin

• Publisher: Elsevier Science
• Year: 1954
• Weight: 818 KB
• Volume: 20
• Category: Article
• ISSN: 0031-8914
• DOI: 10.1016/s0031-8914(54)80049-8

✦ Synopsis

A method is described to measure refractive indices of gases at atmospheric pressure and at a frequency of 25,000 Mc/s. The method is based on the change in resonance frequency of a cavity, first filled with a reference gas (nitrogen) and after that with the gas of which the refractive index is to be determined. However, instead of measuring the frequency change of a fixed cavity, we measure the change in length of the cavity, necessary to keep it tuned in both cases to the frequency of the {6,6) inversion line of ammonia. Subsequently the reading with a nitrogen filling is compared to the one of the evacuated cavity, so that all refractive indices are obtained with respect to vacuo. Results of these measurements for ten gases are given. As the absorption is extremely small and the inaccuracy of our measurements of refractive indices amounts to one or two parts in 106 for these gases, the introduction of a complex refractive index is found to be unnecessary.