Low-Frequency Dynamics of Homogeneous Four-Level cw Lasers

Abstract

The response of homogeneously broadened four‐level lasers to known pertubations is investigated theoretically and experimentally with a Nd:YAG laser. Considered are cavity loss modulations in the low‐frequency range including the relaxation‐oscillation regime separately from shifts of the cavity frequency. The experiments are carried out in such a way that the population inversion is also spatially homogeneous. This allows us to simplify the theories. Good agreement is obtained between experimental and theoretical results. In the case of loss modulation the laser response exhibits one sharp peak in the vicinity of relaxation oscillations. Regular pulses of high peak intensity are obtained which are controllable with very small loss modulations. In the case of a continuous shift of the cavity frequency the laser output consists of similar pulses. They occur at the relaxation‐oscillation frequency independent of the rate of change of the cavity frequency. The laser frequency is shifted away from line center proportional to the third root of the rate of change of the cavity frequency. Mode locking was not found.