Measurement of Iodine Cell Purity and Absolute Frequency Shifts for Laser Stabilization

− This contribution deals with the investigation of uncertainties achievable through stabilization of lasers using saturated absorption in iodine vapour. The main focus is on the iodine cell technology and evaluation. We present results from two independent methods for the measurement of the purity of molecular iodine in absorption cells. The purity was tested by improved method based on measurement of induced fluorescence and evaluation by the Stern-Volmer formula. Original measurement setup was upgraded with a system for compensation of unwanted effects of back-reflected and scattered light and multimode regime of the pumping laser. The modified arrangement results in a significant improvement of reproducibility. The evaluation of absolute frequency shifts caused by iodine cells was measured by direct frequency comparison of iodine-stabilized frequency doubled Nd:YAG lasers. The absolute frequency shift of a reference laser system was calibrated by frequency comparison with a stabilized optical comb locked to the radiofrequency etalon, the measuring system consists of a commercial laser and our stabilization system with 3f technique. Correct function of the stabilization setup was verified through the evaluation of the Allan standard deviations. A series of measurements with a special refillable iodine cell was conducted on both experimental setups for three various levels of impurities. Results of both methods are in a very good correlation and show very high purity of iodine in measured cells. The results also help for definition of procedures for improving iodine cell manufacturing technology at the Institute of Scientific Instruments.