Concentric Two-Portion Radial Polarized Beam with Phase Shift

Focusing property and focal pattern of incident optical beam play an important role in many optical systems, including optical imaging system, optical sensing instruments, and analysis instrument. The focusing properties of concentric two-portion radial polarized beam are investigated theoretically. The phase shift of the center portion is π. Results show that the focal pattern can be altered considerably by adjusting the radius of dividing circle between the two concentric portions. With increasing radius, focal spot broadens along optical axis, and splits into two peaks, and then combine back into one peak again. In this evolution process, the local intensity minimum zone may also occur. For certain radius, the focal spot may shrink, which means super-resolution effect appears, and at the same time, focal depth can also be widened, which is very useful in many optical systems, for example increase resolution in imaging instruments.