Precise frequency measurements of CO2/OsO4 and HeNe/CH4-stabilized lasers

New frequency measurements near 29 THz have been performed with a resolution of about plus or minus 1.7 x 10 to the -12th (1 sigma) on an OsO4 stabilized (C-12)02(R-16)(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 (C-12)O1 (O-16)2 R(12)/OsO4 stabilized as a reference.