| 摘要 |
PURPOSE:To widen a jitter measuring range by allowing a reflected light from a rotary polygonal mirror to be made incident on a photodetector through an acousto-optical element. CONSTITUTION:A laser beam emitted from a laser oscillator 1 is made incident on a rotary polygonal mirror 2, and swept by utilizing the variation of a reflection angle of the laser beam caused by the rotation of the polygon mirror 2. In this case, an acousto-optical element 3 is provided on an optical path of the laser beam which is swept, and the ultrasonic wave of a prescribed frequency is always given to the element 3. In this state, in the laser beam which is swept, only a laser beam having an incident angle for satisfying a prescribed expression is brought to optical polarization. Subsequently, in a photodetector 4, when the incident laser beam to the element 3 has an incident angle which satisfies the prescribed expression to the utmost, the maximum output is obtained. In the same way, sweep is executed several times, and from a fluctuation portion of an obtained output waveform, a time fluctuation portion is derived in a data processing part 5, and a jitter portion of the polygonal mirror 2 is measured. |
