Causes of scatter of the emission frequency of gas lasers stabilized using the Lamb dip

Frequency shifts of the order of tens of megahertz were induced by misalignment or asymmetric stopping down of a resonator of a compact He–Ne laser the emission frequency of which was stabilized using the Lamb dip. These shifts were due to the fact that motion of a mirror along the resonator axis was accompanied by angular scanning because of the excitation of higher harmonics of mechanical vibrations of a mirror together with its piezoelectric ceramic base. Parasitic amplitude modulation produced by such vibrations shifted the frequency of the power minimum. In the case of symmetric stopping down of the laser the shift of the emission frequency did not exceed 2–4 MHz, indicating that in this case the Garside effect and the lens-like action of the inhomogeneous population inversion region had little influence.