CURRENT PUSHING OF THE OSCILLATION FREQUENCY OF A 6328-Å He–Ne LASER

Abstract

Increasing the discharge current through a small dc‐excited 6328‐Å laser changes the index of refraction of the discharge and causes a blue shift of the laser oscillation frequency of ∼1 MHz/mA. The shift is independent of laser cavity tuning and decreases with increasing dc discharge current. Approximate calculations plus other experiments indicate that this shift represents the dispersive effects of the strong 6334‐Å and 6402‐Å upward transitions from the neon 1s₅ metastable level. The residual spectral width and FM noise in stable 6328‐Å lasers, especially as compared to 1.15‐μ lasers, may be due to plasma disturbances acting through this dispersive mechanism, rather than to microphonic disturbances as commonly suggested.