Negative feedback in an actively mode-locked laser

An investigation is made of the stability of a nonautonomous system of equations describing the operation of an actively mode-locked laser. A proposed model of the laser takes account of the following effects on a pulse with a steady-state profile during one round trip in the resonator cavity: a bandwith-limited gain, which increases the pulse duration, and periodic amplitude modulation, which reduces this duration. The influence of the passive losses in the cavity is also included in the model. Stabilisation of the lasing kinetics is detected and analysed. Active mode locking has the properties of negative feedback with a coefficient inversely proportional to the average output power. This behaviour of feedback is associated with the narrow-band nature of the amplification of ultrashort pulses in the laser.