| 摘要 |
A refractometer for estimating the refractive index of a substance on the basis of light reflected from an interface (83) between a prism (80) and the substance (82) or refracted into the substance (82), including an intensity profile detector (88) for the reflected or refracted rays throughout a range of angles of incidence of the rays, and an intensity profile analyzer for locating a singular property of the resultant intensity profile curve as a function of a multiplicity of at least three intensity values along the intensity profile and for indicating the index of refraction of the substance (82) from the location of the singular property, and a method of determining refractive index and of controlling a process using corresponding method techniques. In preferred embodiments: the analyzer is adapted to form derivatives of the resultant intensity profile curve; the singular property is an approximate singularity of the first derivative, which is located by determining the point where the second derivative crosses zero; and the prism (80) comprises a section of a cylinder, the interface (83) being a curved surface thereof in which the intensity profile shifts linearly along the image plane (30) with change in the critical angle theta c albeit with partially reflected rays that fall both above and below the point that corresponds with the critical angle position theta c.
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