Nikon Corporation

Kouichi Tsukihara

Jun Kawakami

Hitoshi Kawai

Akira Ishida

Hitohsi Kawai

A second harmonic generation (SHG) device is used for conversion of wavelength. The direction of polarization of light beams is suitably rotated by a direction-of-polarization rotating unit, for example by 45.degree., and thereafter these light beams are guided into the SHG device. This can minimize attenuation of intensity of light beam due to conversion of wavelength. Hence, using this direction-of-polarization rotating unit in the apparatus for measuring the medium, the intensity of light being incident upon the photodetector can be increased, whereby the refractive index of the medium can be measured more accurately than by the conventional apparatus.

Apparatus for measuring refractive index of medium using light,

The present invention relates to an optical interference measuring apparatus and method for measuring displacement of an object. The apparatus and method reduces the displacement-measurement error caused by changes of the refractive index of the atmosphere or the like, in a measurement optical path and a reference optical path, by suppressing crosstalk caused by unfavorable mixing of reference light and measurement light with each other, thereby improving accuracy in the measurement. The apparatus produces interference between a measurement light beam and a reference light beam. The measurement light is propagated through a measurement optical path including a measurement reflector, which is at least movable along the measurement optical path. The reference light is propagated through a reference optical path including a reference reflector. The interference occurs in a predetermined interference system, whereby the displacement of the measurement reflector can be measured. The apparatus, especially, comprises a light path separating system for spatially separating from each other the optical path from the measurement reflector to the interference system, through which the measurement light is propagated, and the optical path from the reference reflector to the interference system, through which the reference light is propagated.

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Ota, Japan

Kouichi Tsukihara