Adaptive optics system prototype for the automatic control of geometrical fluctuations in a laser beam in air

In this paper we present a prototype of an adaptive optics system developed for the control of geometrical fluctuations in a laser beam in air and based on the interferometric detection of the beam phase front. We show that this technique is very effective also when high sensitivity and high band-pass are required for correction of small perturbations. The working principle is also very simple and direct. In fact, the laser beam is made to interfere with a reference beam, properly obtained, and the phase difference is read by means of an array of photodiodes. A digital control system acquires the output signal from the array, computes the error signals and generate the correction signal, sent to the deformable mirror. In the paper we discuss some experimental results, the limits of the prototype and future developments and improvements.