| 摘要 |
PROBLEM TO BE SOLVED: To solve a problem that the efficiency of laser light having a wavelengthλ1 is lowered when a diffraction grating 1a for the laser light ofλ1 is designed while depending on laser light having a wavelengthλ2 or efficiency of the laser light ofλ2 is lowered conversely when a diffraction grating 1b for laser light ofλ2 is designed while depending on the laser light of the wavelengthλ1 in a conventional optical member. SOLUTION: The diffraction gratings 1a and 1b are formed so that projecting parts 1a1 and 1b1 and recessed parts 1a2 and 1b2 can be respectively alternately formed on the surfaces thereof and the width dimension of the projecting parts 1a1 and 1b1 can be different from that of the recessed parts 1a2 and 1b2. While defining projecting part width/(projecting part width + recessed part width) as a DUTY ratio, the optical member is designed while changing this DUTY ratio. Thus, design is enabled while changing efficiency in the 0th-order diffracted light and 1st-order diffracted light of laser beams.
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