JP2540223B

PURPOSE:To prevent a distortion of waveform for an electrical signal to be measured and to detect a voltage more exactly by irradiating a point to be measured and a reference point alternately with a light beam deflected by an optical polarizer. CONSTITUTION:The light beam which is emitted from a laser diode 14 and made incident to an optical probe 12, is deflected at high speed between the points A(A1-A3) to be measured on a dielectric multilayer film mirror 12A and reference point B in the manner of driving the optical polarizer 8 capable of two-dimentionally deflecting the light beam by a driver. In this case, the distortion of electrical signal to be measured due to the ON/OFF operation is not produced since an electrical chopper is not used; the exact voltage can be detected accordingly. When the light beam is deflected between the points A to be measured and reference point B at high speed, the difference in reflectances of them is detected by an optical detector 22, but the output of detector 22 is corrected by using the output of an optical detector 23 which is capable of obtaining the same output, and further by means of amplifying the outputs of difference at the time when the points A to be measured or reference point B are irradiated with the light beam, by a synchronous amplifier 27, the voltage can be sensitively detected with low noise.