We present what we believe is a novel technique based on the moiré effect for fully diagnosing the beam quality of an x-ray laser. Using Fresnel diffraction theory, we investigated the intensity profile of the moiré pattern when a general paraxial beam illuminates a pair of Ronchi gratings in the quasi-far field. Two formulas were derived to determine the beam quality factor <i>M</i><sup>2</sup> and the effective radius of curvature <i>R</i><sub>e</sub> from the moiré pattern. On the basis of the results, the far-field divergence, the waist location, and the radius can be calculated further. Finally, we verified the approach by use of numerical simulation.
© 1999 Optical Society of America
(120.4120) Instrumentation, measurement, and metrology : Moire' techniques
(140.0140) Lasers and laser optics : Lasers and laser optics
(140.7240) Lasers and laser optics : UV, EUV, and X-ray lasers
(340.0340) X-ray optics : X-ray optics
Jun Yang, Dianyuan Fan, Shiji Wang, and Yuan Gu, "Technique for diagnosing x-ray laser beam quality by use of the moiré signal," J. Opt. Soc. Am. A 16, 323-330 (1999)