5B1 - Measurement of saturation induced optical nonreciprocity in a ring laser plasma

When a gas laser plasma is illuminated by unequally intense laser beams traveling in opposing directions, its index of refraction becomes significantly nonreciprocal. We have studied this effect by measuring the beat frequency between the counter-rotating beams in a 6328Å He-Ne ring laser under controlled conditions. Frequency locking was effectively eliminated by using a Faraday effect beat frequency bias element. The measured beat frequency became a strong function of two independent parameters: the ring resonator tuning and the beam intensity difference. A second Faraday effect element was introduced to control non-reciprocal losses within the ring resonator. Servo loops controlling both the total laser intensity and the intensity ratio between the counterrotating beams permitted direct measurement of the non-reciprocal gain caused by saturation, or hole burning. The effects observed are contained in Aronowitz' theoretical description of ring lasers.