| 摘要 |
PURPOSE:To accurately measure a discontinuous part on the objective surface to be measured by changing over at least >=2 rays of light with different wavelengths and measuring in order the phase lag quantity of the rays in accordance with the distance to the objective surface to be measured. CONSTITUTION:A laser light source LZ 2 generates the plural coherent rays of light with different wavelengths selectively. An acoustoptic modulator AOM shifts frequency of the rays at the reference side in order to detect the phase lag of the rays heterodyningly. A modulated signal source OSC drives the modulator AOM with the prescribed frequency fb. A phase detector PD detects the phase lag quantity included in output of a photodetector D2. An arithmetic circuit CON2 calculates the distance to the objective surface OBJ to be measured from the relation between the wavelength of the rays used for measurement and the phase lag quantity at that time. Then, first, the light source LZ2 generates the rays with the optional wavelength in order. In this way, the phase lag quantity corresponding to each wavelength is measured PD in order. The distance to the objective surface OBJ to be measured is calculated by working out these measured results as the prescribed simultaneous equations with the arithmetic circuit CON2.
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