Precise Frequenccy Measurements of CO2/OsO4 and HeNe/CH4-Stabilized Lasers

New frequency measurements near 29 THz have been performed with a resolution of about ±1, 7 10-12(1σ) on an OSO4 stabilized 12CO2 16R(10) laser. To this end, a new low-noise synthesis chain using two FIR optically pumped phase-locked lasers and a good spectral purity quartz oscillator at 1.06 GHz have been developed. In order to allow comparisons with previous measurements, a new measurement of the CH4 stabilized HeNe laser was made using a 12CO1 16O2 R(12)/ OSO4 stabilized as a reference.