Stabilized CO2 /OsO4 laser with a frequency reproducibility of 10–12

A CO₂/OsO₄ laser stabilized by saturated absorption was constructed. Its long-term instability was 5×10^–13 in several hours and the error in the frequency reproducibility was 10^–12 from shot to shot. This reproducibility was achieved by developing a method for the control of the frequency shift caused by amplitude modulation and gas lens effects. The method was based on an analysis of the profile of the derivative of a reference line. The fundamental collisional shift of the working transition in OsO₄ was found experimentally: at pressures in the range ~ 1 mTorr the shift did not exceed ±10^–12 when the pressure was altered by a factor of 2. An important factor which limited the frequency reproducibility of a laser with an external nonlinearly absorbing cell could be the misalignment of the opposite beams in the cell.