Removal of Zero-Order Beam Interference using Dammann Grating Grayscale Map
Zero-order beam interference is generated at the focal plane when the liquid crystal spatial light modulator(LCSLM)is loaded with a computer-generated hologram(CGH)during laser beam splitting.To address this issue,we proposed to load a Dammann grating grayscale map to LCSLM using phase extinction interference,thereby removing zero-order beam interference.Based on the simulated annealing algorithm,the set of phase turning points was solved;simulations were performed in VirtualLab;and a script for generating Dammann grating grayscale maps was written using MATLAB software.Consequently,a verification system was built based on a liquid crystal on silicon spatial light modulator(LCOSSLM),and its modulation effect was tested.The results show that the zero-order beam interference is removed in the CCD field of view by loading the Dammann grating grayscale map for laser beam splitting.Moreover,the actual beam-splitting effect is close to that observed in the simulation results.Furthermore,the beam-splitting uniformity under one-dimensional five-beam splitting reaches 97.190%,which is better than the modulation effect of the grating CGH generated by the GSW algorithm.When the focal distance is large,effects of one-dimensional two-and seven-beam splitting are observed with beam-splitting uniformity levels of 98.453%and 96.820%respectively.The two-dimensional beam splitting is also observed with a measured beam-splitting uniformity of 95.436%.In addition,no zero-order beam is observed in the CCD field of view.
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