When areas sectioned by p circumferences centered on a predetermined position are set on a beam cross section of light input to the optical phase modulator 15, the more outside each of {HEAD ~ the areas} is, the wider the radial width of the area, the amount of phase modulation is constant in each of the areas, and the amounts of phase modulation differ by {TAIL ~ π} between two adjacent areas out of the areas 
When areas sectioned by p circumferences centered on a predetermined position are set on a beam cross section of light input to the optical phase modulator 15 , the more outside each of { HEAD ~ the areas } is , the wider the radial width of the area , the amount of phase modulation is constant in each of the areas , and the amounts of phase modulation differ by { TAIL ~ π } between two adjacent areas out of the areas
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