Absolute measurement of submillimetre and far infra-red laser frequencies

The frequencies of the hydrogen cyanide and water vapour laser emissions have been measured directly against a fundamental frequency standard by harmonic generation and mixing and beat frequency detection in point contact diodes. The value obtained for the HCN laser (337 ¿m) is 890 760.2 ± 0.2 MHz and for the H2O laser (118 ¿m) 2 527 952.5 ± 1.5 MHz. In addition some preliminary measurements have been made on the 10.7 THz H2O laser line.