GENERATION OF COHERENT WAVE-FRONTS AND IMAGES INSIDE LASER RESONATORS

We describe a new type of laser mode filtering using two complementary spatial filters located against the plane mirrors of a confocal lens resonator. With Nd/YAG as amplifying medium, we report the synthesis o f two particular waves : a sinusoidally modulated wavefront, and a uni phase beam with a flat spatial profile and minimal divergence. The tem poral evolution of the beam under construction is also recorded. The p rocess is a new type of wavefront reconstruction, like holography, but without reference.