GB1502613A - Optical measuring apparatus - Google Patents

Abstract

1502613 Photo-electric apparatus for reflectance measurement FERRANTI Ltd 4 Aug 1975 [3 Aug 1974] 34321/74 Heading G1A Photo-electric apparatus is provided with a reflective detector such that merely by movement of the sample, the transmittance as well as the reflectance of the sample may be measured. Light, ultraviolet or infrared radiation from a source 10, which may be filtered to restrict it to a particular wavelength, is directed by lens 11, via stop 12, to a silicon photo voltaic detector 13, whose face is polished for 35-50% reflection, and which is angled slightly to the incident beam, so as to direct reflected light 16 to the back 12' of the stop, where it is absorbed. For reflectance measurement the sample is moved into the path of the beam 16 reflected from the detector and the detector output compared with that when no sample is present (Fig. 1 arrangement). For transmittance measurement, the sample is moved into the beam 15 incident on the detector and the detector output compared with that for the Fig. 1 arrangement. The sample may be mounted in a holder which moves along a path which is a circle centred on the detector; or two holders may be provided, one in the detector incident path and one in the detector reflected path, these holders normally allowing light to pass through, and into each of which in turn the sample may be mounted. The lens arrangement may be such as to provide convergent or divergent beams, or the detector surface may be concave or convex. One requirement is that all the light reflected from the detector is incident on the sample and vice versa. The detector may be coated to aid reflection therefrom.