FREQUENCY-SHIFTS OF IODINE STABILIZED HE-NE LASERS AT HIGHER HARMONICORDER STABILIZATION

The frequency shifts of an I-127(2) stabilized He-Ne laser at 633 nm h ave been measured at the third, fifth, and seventh harmonic stabilizat ion using a digital signal processing lock-in amplifier, The observed frequency shifts confirmed the previous theoretical prediction that th e laser frequency depends on the harmonic order of stabilization. The lower effects of modulation amplitude shift, power shift! and iodine p ressure shift at the fifth harmonic stabilization indicate a potential improvement of the frequency reproducibility of the laser standard. A model is suggested to describe the power shifts of the laser, The mec hanism explains the lower power shift of some lasers when they are ope rated at relatively high intracavity power.