GB438511A - Improvements in or relating to spectrophotometers - Google Patents

Abstract

438,511. Photometric apparatus. HILGER, Ltd., A., 98, King's Road, Camden Road, London, and PINEO, O. W., 60, Main Street, Milo, Maine, U.S.A. March 19, 1934, No. 8635. [Class 97 (i)] Relates to spectrophotometers in which the light-reflecting &c. power of a specimen is compared with that of a standard by using polarized light with a flicker device for varying the illumination of the specimen and that of the standard in a complementary manner. According to the invention the planes of polarization of the two beams by which the specimen and standard are illuminated are caused to rotate or oscillate together and the beams are then passed through a stationary polarizing device so that they emerge with a fixed plane of polarization and varying intensity to give the required flicker illumination of the specimen and standard. To enable the tests to be carried out in substantially monochromatic light from any desired part of the spectrum, the illuminating beams are derived from a monochromator. In the form shown, light passing through the exit slit 1 of the monochromator is received by a Nicol prism 2 from which it emerges as a plane polarized beam. It then passes through a Wollaston prism 3 and emerges as two beams polarized in planes at right-angles to each other and slightly divergent, the relative intensities of these beams being variable by rotating the prism 2 about the optical axis. The beams from the prism 3 pass through a rotating half-wave plate 4 which produces periodically varying retardations of the beams, with a phase difference of 90‹ between them. The beams then enter a fixed Nicol prism 5 and emerge with the same fixed plane of polarization but with intensities which vary in a complementary manner, owing to the abovementioned phase difference. They are then passed through part lenses 6 to increase their divergence and enter an integrating sphere 8 to fall on the specimen 9 to be tested and a standard 10. Light leaves the sphere 8 through a window 11 to fall on a photoelectric cell for detecting the flicker, the amplified current from the cell being preferably used to operate means for rotating the prism 2 until the cell is equally illuminated by the specimen 9 and standard 10. Means are described for automatically adjusting the width of the slit of the monochromator as the slit is moved along the spectrum, in such a way that in all positions the wave-length range, or the vibration frequency range, of the light passing through the slit is the same.