Self-stabilization of argon laser generation mode with a nonlinear absorber inside the cavity

The laser generation mode in the form of periodic light pulses requires a high stability of repetition period in order to ensure the reliability of information transfer or the accumulation of measurement results, with the pumping and sensing technology. The simultaneous presence of amplifying and an absorbing medium ensures a change in the optical path of laser cavity, both upward and downward. The experimentally obtained results showed that the dependence of frequency shift between longitudinal laser modes on the values of unsaturated gain and absorption is linear. The values measured within an accuracy of 1 khz showed that the instability of output energy and time characteristics of laser is significantly lower than the ripple of the input voltage of power supply. On the basis of obtained dependences, a calculation procedure is shown for the stability of repetition rate of light pulses in the mode of synchronization of longitudinal modes, which correspond to measured values of width of the beat signal between modes. Simultaneous fluctuations of discharge current in the amplifier and in the absorber are mutually compensating. As a result, the change in the repetition rate of light pulses turns out to be an order of magnitude smaller than in the case of active mode locking of an argon ion laser. Fluctuations in the average radiation power (light pulse energy) decrease with an increase in absorption and, at high absorptions, can become lower than in the free-running laser mode. An essential result is the experimental confirmation of the effect of the difference in saturation conditions between the amplifier and absorber, which is determined by the geometry of cavity, namely, the ratio of the beam cross section in the amplifier and absorber on stability of generation mode. (author)