Measurement of Interferometric Secondary Wavelength Standards in the Near Infrared*

Abstract

High-precision absolute interferometric wavelength determinations in the lead sulfide region of the infrared are reported. Very thin silver films were used to coat the etalon plates. In this way sufficiently high reflectivity in the visible region for high precision measurements without prohibitively high absorption in the infrared was obtained. In addition the correction due to phase penetration in these films is relatively small. The “Stadia Method,” which was used for all measurements, made it possible to achieve a precision in wavelength measurements using energy integrating detectors comparable to that which may be obtained photographically in the visible using high-reflectivity films. In addition a technique was developed which made it possible to measure absorption lines interferometrically relative to an emission line.Three infrared wavelengths of mercury-198 were measured in emission and the wavelengths of P(16), P(10), P(1), R(7), R(14), and R(17) of the 002 band of HCN were measured in absorption relative to mercury-198 λ5460 A. The band origin ν0 of the 002 band was determined from these measurements using values of B′ and B″ previously reported from measurements on lines of high J number. The band constants were then recomputed using the new value of ν0. Final results are:Hg198 λ10 140 A9859.4342±0.002 cm−1Hg198 λ13 570 A7366.866±0.005 cm−1Hg198 λ15 295 A6535.8855±0.002 cm−1002 band of HCN ν0=6519.6148±0.003 cm-1B′=1.457063B″=1.478225.