Photonic crystal changes coherent laser to incoherent laser with random phase

It is revealed that the phase-shift and polarization properties of laser beam reflected from a photonic crystal (PC) are sensitive to the surface-layer thickness of the PC. A continuous variation of λ/4 in surface-layer thickness produces a continuous change of π in the phase-shift. Besides, in the case of an asymmetric coupled-defect PC, various polarization patterns including linearly polarization in different directions, circular polarization, and different elliptical polarizations, will appear simultaneously within one laser beam. In this paper, a PC with modified surface-layer thickness is designed to induce incoherent laser irradiation with random phase at the focus point of the reflected field. This scheme will satisfy the increasing requirements for incoherent laser irradiation.