| 摘要 |
PROBLEM TO BE SOLVED: To provide a multi-beam optical system which prevents a beam array from being curved on a plotting face regardlessly of inclusion of a curved surface mirror. SOLUTION: A laser luminous flux emitted from a laser light source is branched as parallel rays of luminous fluxes by a diffraction branching element 30. Converging optical system makes beam axes of branched luminous fluxes parallel with each other and converges them on a multi-channel AOM respectively. Plural curved surface mirrors included in this converging optical system satisfy a following conditional expression as the whole. In the expression,θi is the angle of inclination between the beam axis of non-diffracted light transmitted through the diffraction branching element 30 and the optical axis of the i-th curved surface mirror, and Ai is +1 in the case where the beam axis of specific diffracted light branched by the diffraction branching element 30 is on one side of the beam axis of non-diffracted light, and Ai is -1 in the case that it is on the other side, andωo is the beam diameter at the time of passing the diffraction branching element, andωi is the beam diameter at the time of incidence on the i-th curved surface mirror.
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