| 摘要 |
PURPOSE:To enable stable temperature measurement, by focusing using a plurality of mirror surfaces containing at least one concave mirror in an optical system to meet changes in the atmosphere in a furnace such as variation in the refractive index of a medium. CONSTITUTION:A flat mirror 1 and a concave mirror 2 are arranged as radiation light focusing means in an HIP unit. An incident light is led to a concave mirror 2 by changing the direction thereof with the flat mirror 1 to be focused to a light receiving section 3. This requires only the use of a mirror surface without using a lens or the like designed for use in air at a normal temperature and pressure thereby making the HIP unit free from the effect of a medium gas refractive index. Thus, the optical system is adjusted even for changes in the medium gas refractive index thereby enabling stable temperature measurement.
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