New fields of X-ray source applications (X-ray laser and high order harmoni
c generation) could appear if an intensity higher than 10(12) Wcm(-2) is re
ached. Following this goal, we have started a complete investigation of the
X-ray beam wavefront both numerically and experimentally. The first XUV wa
vefront sensor has been developed and tested on different XUV sources. For
a better comprehension of the experimental results, a numerical work (ray-t
race code) has been performed. We present and discuss the first results obt
ained on the X-ray laser at 21.2 nm.