Technique for diagnosing x-ray laser beam quality by use of the moire signal

We present what we believe is a novel technique based on the moire effect f or fully diagnosing the beam quality of an x-ray laser. Using Fresnel diffr action theory, we investigated the intensity profile of the moire pattern w hen a general paraxial beam illuminates a pair of Ronchi gratings in the qu asi-far field. Two formulas were derived to determine the beam quality fact or M-2 and the effective radius of curvature R-e from the moire pattern. On the basis of the results, the far-field divergence, the waist location, an d the radius can be calculated further. Finally, we verified the approach b y use of numerical simulation. (C) 1999 Optical Society of America [S0740-3 232(99)01502-1].