High-precision measurement of the center frequencies of the hydrogen cyanide (HCN) hyperfine transitions in the 1.5 μm wavelength band

The definition of both meter and second relies on precisely measured frequency. The convenient sources of such frequencies are lasers stabilized by molecular vapours. The He-Ne lasers stabilized by iodine vapours represent the cornerstone sources in the visible spectrum. On the other hand, the infrared spectrum (particularly 1550 nm C-band) is of metrological interest thanks to its cost-effective, readily available components. The widely used absorption media at 1550nm has been two acetylene isotopes (12C2H2, 13C2H2), while H13C14N represents an alternative covering a broader spectrum well corresponding to the telecommunication C-band.