Amplitude and Frequency Stabilization of an Internal-Mirror He–Ne Laser

Both the amplitude and the frequency of an internal-mirror He–Ne (λ=633 nm) laser are stabilized simultaneously by a new simple method. The total back beam intensity is detected with a silicon photodiode. The electric voltage signal proportional to the total back beam intensity is applied to a dc servomotor which rotates a cooling fan controlling the laser tube length change due to thermal expansion; consequently the laser amplitude and frequency are stabilized at the same time. The relative amplitude stability of ±0.1% and the relative frequency stability of ±5×10 -9 are obtained over a period of 10 minutes or longer. Each power output of mutually orthogonal components of polarization is also stabilized.