Deviation of light beam from their path caused by partial obstructions of wave front may be called diffraction. Basics of diffraction is: when x-rays interacts with materials, coherent scattering occurs throughout atomic scattering center, x-rays will be in phase and may be amplified with certain direction, when materials with crystalline structures. In unit cell, intensity of the amplified x-rays can be used to workout of atoms arrangement.
The spreading is results of partial obstruction of sharp edge. Same as light wave, sound wave shows diffraction pattern. This patterns shows rapid decrease in intensity of light or sound with increasing distance from center of the pattern. Diffraction is described by scientists:
Young’s experiment: In this experiment, Young showed that light having interference pattern, and it proved that light have wave property. In this experiment four conditions are important: 1) Coherent source, which emits light waves always in phase of same wavelength and frequency. 2)polarization, same polarization wave disturbance. 3) Amplitude, same amplitude of two sets of waves. 4) Path difference, between two light waves should not be too good.
In Young's experiments, when source slits is moved nearer to the double slits, then fringes separation is unaffected but their brightness increases. And when separation between slits decreases then separation of fringes increases.
Fraunhofer diffraction: It is a far field diffraction, we could assumed light rays are approximately parallel. 1) Single-slit diffraction is consider as Fraunhofer diffraction through slit of width. We can see in fig. that relative maxima is about half way between the minimum value zero. Circular aperture it is maximum used and having great interest because maximum light experiment instruments are circular, such as optical systems. Because maxima and minima from concentric rings, and airy disk, is central bright maxima.