Phase control of a laser beam by supersonic gas jets

Active phase control of high power density lasers could be achieved by using gas jets with controllable optical density variations. Experiments have been carried out on a double jet system in which the effective optical density of one of the jets is made variable by using a simple mechanical control system. Interferometric data are used to study the structure of the jets and to measure the phase shifts. When operated with combinations of He and a He-Ar mixture, the phase shifts introduced into a HeNe laser beam range from pi to 3 pi. Photographs of the asymmetric far field diffraction patterns which result from passing a clean laser beam through the jets are presented and are shown to compare well with theoretical predictions. Additional far field photographs are used to show that good compensation is achieved when a simply distorted laser beam is passed through the jets.