X-ray pulse stretching after diffraction

The development of ultrashort X-ray pulse sources requires optics that keep the pulse length as short as possible. One source of pulse stretching is the penetration of the pulse into a crystal during diffraction. Another source is the inclination of the intensity front when the diffraction is asymmetric. The theory of short X-ray pulse diffraction has been well developed by many authors. As it is rather complicated, it is sometimes difficult to foresee the pulse behavior (mainly stretching) during diffraction in various crystal arrangements. In this article, a simple model is suggested that gives a qualitatively similar shape to the diffracted pulse which follows from exact theory. It allows proposal of what experimental arrangement is optimal to minimize the pulse stretching during diffraction. First, the effect of pulse stretching due to penetration into a crystal surface is studied. On the basis of this, the pulse profile change during diffraction by two crystals, either symmetric or asymmetric, is predicted.