| 摘要 |
PURPOSE:To obtain an optical and an electric system which both have a fast response speed and take a fast measurement of displacement by using an element of electrooptic crystal, etc., to adjusts the optical path length of reflected light. CONSTITUTION:Light from a laser oscillator 1 is reflected partially by the surface of the wavelength plate 4 of a beam splitter cube BSC2, and ther remainder is reflected by a body 13 to be measured. Those reflected light beams rech a BSC26 through the BSC2 and electrooptic crystal (element varying in refractive index on the lateral and longitudinal axes when impressed with a voltage) and is split into two thereat, and they interfere with each other after passing through polarizing plates 27 and 28. Then, interference signals are converted by photodetectors 29 and 30 into electrical signals, whose difference is amplified by a DC differential amplifier 31. The levels of the interference signals relat to the optical length difference between the two interfering light beams B1 and B2 and a negative and a positive voltage are developed accoring to the displacement of the body 13 to be measure, so the voltage is amplified by an amplifier 32 and fed back to the crystal 25. For the purpose, the relation between the impressed voltage to the crystal 25 and the optical path length difference is calibrated previously and then the displacement of the objective body 13 is obtained by measuring the voltage to the crystal 25. |
