Automatic beam alignment system for a pulsed infrared laser

A fully automatic alignment system for a pulsed infrared laser beam (5 ns pulses, 10 Hz repetition rate, 1.3 microm wavelength) was developed and tested. It compensates for long-term fluctuations of the beam initial position and direction-the automatic realignment is performed every 10 min, and lasts typically 1-2 min. The system adjusts the beam initial position with a maximum error of 0.5 mm (10% of the beam diameter) and the beam direction with a maximum error of 50 murad. The solution is based on two InGaAs quadrant photodiodes as the position detectors and two motorized mirrors controlled by a personal computer. The signals from the quadrant detectors are processed by a peak detector and digitized by an analog to digital converter, which is synchronized with the laser pulses.