Spectral purity and long-term stability of CO2 lasers atthe Hertz level

Ultra-high-resolution spectroscopy and metrology require very stable lasers with a high-spectral purity. For spectroscopy with a resolution in the range 10-100 Hz at 30 THz, we are developing a new stabilization scheme which acts separately on the long and short term stabilities. We present the results achieved with the first part of our new scheme, which is based upon the stabilization on a saturation signal detected in transmission of an active Fabry-Perot cavity. With a laser linewidth of 3.4 Hz (FWHM) and a flicker plateau of 0.7 Hz (Δν/ν=2.10^-14) obtained using a strong OsO₄ line as reference, this stabilization system already improves the both short and long-term stabilities obtained by our previous setup which involved an external cell instead of a Fabry-Perot cavity. We present also the results using a CO₂ laser line as frequency reference