This paper presents the detailed analysis of a frequency stabilized internal-mirror He-Ne laser (λ=633 nm) controlled digitally by making use of the dependency of the intensities of two orthogonal polarization modes on frequency detuning. A laser tube containing an equivolume mixture of Ne
20 and Ne
22 was used in the experiment. Frequency stabilities were evaluated in terms of the resolutions of the digitization of polarization mode intensities. A 14-bit resolution system provided a stability of better than 10
-10 for the integration time of 0.1 to 250 [sec] while lower resolution systems exhibited lower stabilities. It was found that the flexure of the laser tube due to thermal expansion slightly changed the detuning characteristics and limited long-term stability.
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