| 摘要 |
PURPOSE:To accurately measure the tilt angle of an optical axis from the output of a light spot position by controlling the setting of a light spot position detector on the focal plane of a lens placed in a parallel optical path. CONSTITUTION:A half-mirror 2 is placed in parallel laser luminous flux 1 whose optical axis is to be measured to obtain reflected light 3. The reflected light 3 is converged on the light spot position detector 5 by using the lens 4. This light spot position detector 5 has a focus position detecting function and outputs a focus position detection signal to a focus servo circuit 6, which sends a signal to an actuator 7 to perform position control so that the light spot position detector 5 is in the focal plane of the lens 4 at all times. At this time, an output proportional to the tilt angle theta of parallel laser luminous flux 1 appears at the position output terminal 8 of the light spot position detector 5. Consequently, an error in detection generated owing to variation in the distance between the lens 4 and light spot position detector 5 is eliminated.
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