A stabilized mode-locked Nd:YAlG laser using electronic feedback

Techniques for constructing a stable mode-locked Nd:YAlG laser source suitable for long term unattended operation are described. These techniques involve the use of two types of electronic feedback loops-the oscillator loop and the servo loop. An additional auxiliary loop to provide for long term operation is described and demonstrated. The detuning properties of the mode-locked laser, using both intracavity loss and phase modulation, are obtained experimentally for the open loop. It was found that the loss-modulated mode-locked laser was noisy due to relaxation oscillations. However, the use of a phase-modulated mode-locked laser presented other problems due to the possibility of a spontaneous 180 ° switch in envelope phase of the pulses. A technique for quenching this phase switching is described. The results of applying these techniques led to the experimental demonstration of a mode-locked Nd : YAlG laser that operated for long times (48 h), with an error rate (dropping a pulse or mistiming of a pulse) of
1.4 \times 10^{-10}
, with and rms variation of 8.2 percent in the second harmonic at 0.53 μm and with an absence of relaxation oscillation.