Simultaneous phase-lock of five CO2 lasers to a primary Cs frequency standard

The output of a CO2 laser, operating on the PI(18) transition of (C-13)(O-16)2 at 26941 GHz (11.128 microns) was phase-locked to a 5 MHz signal from a primary Cs frequency standard by means of a frequency chain having only CO2 lasers as infrared sources. Simultaneously, four other CO2 lasers in the chain were phase-locked to the 26941 GHz output. This provided CO2 laser frequencies at 26 450 305, 26 940 815, 28 694 625, 29 442 480, and 33 185 715 MHz having zero long-term-average frequency error relative to the Cs standard, and the + or - 10 to the -13th (about 3 Hz) long-term absolute uncertainty of the standard.