Wavelength of the CH4 line at 3.39 μm

Optical frequency measurement: 40 years of technology revolutions

“…This moved the speed of light up by 0.6 m/s, corresponding to a wavelength shift of , only half the nominal uncertainty zone of the Kr lamp-based wavelength standard system. The analogous CO laser speed of light results at NRC [17] and the confirming wavelength values for methane by NRC [18] and NIST-Gaithersburg [19] supported the proposed speed of light number. The CCDM in 1973 was able to recommend a value for the speed of light, with accuracy fixed by the Krypton length standard's uncertainty.…”

The 1973 Least-Squares Adjustment of the Fundamental Constants

“…In the following two sections, we compare selected values of our best WQED and final recommended constants with their appropriate counterparts resulting from the two most recent adjustments; and point out what we consider to be the present major areas of difficulty in the fundamental constants field and the future research necessary to eliminate those difficulties. 34. Changes in the Va'ues of Se'ected Constants…”

“…In table 34.1 we compare our 1973 WQED values for several constants with the similar WQED values given by Taylor Since none of the quantities on the right side of this equation have changed greatly since 1969 (although there have been significant improvements in accuracy), any change in /-L~//-LN between the two• adjustments is reflected as a corresponding inverse change in N A' We also note that the uncertainty in N A is determined 'primarily by the uncertainty in K2.…”

Laser wavelength measurements

“…Systematic errors may also occur owing to the use of separate amplification systems for the two radiations, which may have slightly different time responses introducing different signal delays, particularly if the fringes have different widths [Rowley and Wallard, 1973]. Such electronic problems are avoided in the photographic recording arrangement of Baird et al [1973] and Hanes et al [1973], which uses a spectrograph with a linearly moving photographic plate behind the pinhole to record the intensity changes of both radiations simultaneously. A fundamental disadvantage of continuous scanning methods for a high-finesse interferometer is that it is only for a small fraction of the total recording time that any significant optical flux is detected.…”