Asymmetry studies of iodine resonances and realization of unperturbed molecular transition in a laser standard at 633 nm

A detailed study of the asymmetry of saturated absorption resonances in a laser wavelength standard operating at 633 nm is presented. Analysis of the results for the third and fifth harmonic frequency stabilization techniques has been performed. A new approach in the studies has made it possible to handle the problem of correlated pressure, modulation width and power shifts in the laser standard. As a result, the laser frequency shift due to the resonance asymmetry has been separated from the iodine pressure (inelastic collision) shift. The frequency shift associated with the resonance asymmetry has been shown to increase nonlinearly (quadratically) with the iodine pressure. Collisions with small angle of scattering are found to be the main reason for this effect. The unperturbed molecular transition frequency for the i-component of iodine has been found to be 473 612 214 858.5 +/- 12.7 kHz. The validity of the method is confirmed by frequency measurements performed with a special standard, featuring ten times smaller line asymmetry than that of a conventional laser standard.