Stabilization of the emission frequency of an internal-mirror laser model ILGN-202

The emission frequency of an ILGN-202 internal-mirror laser was stabilized. An experimental study was made of the dependences of the power of the orthogonal components of laser radiation on the frequency tuning in the free-running regime. The laser was stabilized by maintaining a definite relationship between the intensities of the components by an automatic frequency control (AFC) system utilizing the method of thermal control of the resonator length. A theoretical study was made of the ultimate short-term frequency instability and an expression was derived for the transfer function of the optimal AFC system. The relative frequency instability found experimentally was 5 × 10^–9 in 15 min when the averaging time was 1 sec and the change in the frequency in 8 h was 10 MHz.