H. Wang, C.J.R. Sheppard, K. Ravi, S.T. Ho and G. Vienne
Diffraction is a natural phenomenon, which occurs when waves propagate or encounter an obstacle. It is also a fundamental aspect of modern optics: all imaging systems are diffraction systems. However, like a coin has two sides, diffraction also leads to some unfavorable effects, such as an increase in the size of a beam during propagation, and a limited minimal beam size after focusing. To overcome these disadvantages, many techniques have been developed by various groups, including apodization techniques to reduce the divergence of a laser beam and increase the resolution.