Patent GB-672758-A (GB)
Title: Improvements in or relating to spectrometry
IPC: G01J3/28
Filed: 1950-01-12
Abstract: 672,758. Photo-electric spectrometers. GOLAY, M. J. E. Jan. 12, 1950 [Jan. 12, 1949], No. 861/50. Class 40 (iii). In a photo-electric spectrometer the beam for analysis is divided by a rotary slotted disc 27 into a number of distinct beams each of which is interrupted in a characteristic way and these beams after dispersion by a prism 19 or otherwise pass through a second rotary disc 28 with complementary slots, the arrangement being such that the desired radiation through the first slots in disc 27 pass through the first row of slots in disc 28, the undesired radiation passing through other rows of slots in 28. Similarly, the desired radiation through the second row of slots in 27 passes through the second set of slots in 28, and the undesired radiation passes through other slots, and so on. The detecting arrangements are such that the signals received during the first half of each revolution of the discs due to the undesired part of the radiation are balanced against those received during the second half, and the net response is entirely due to the desired radiation, which produces signals only in the second half of the cycle. The Specification indicates a procedure for positioning the slots to produce this effect. In the embodiment shown, the light beam 12 (Fig. 1) from a source 11 after reflection is passed through an entrance aperture 17, and after double dispersion by prism 19 is passed through an exit aperture 18 to be converged on a detector 26, feeding a recorder. The apertures 17, 18 comprise six slits 41-46 (Fig. 2) and 51-56 (Fig. 3), and the light path is cut by two synchronously rotating slotted discs 27, 28 associated with the entrance and exit apertures 17, 18, respectively. The slits in the apertures are such that the desired part of the radiation entering slit 41 would egress through slit 51, 42 and 52 &c. being similarly corresponding slits. The discs 27, 28 are made with slots 48, 49 formed in six discontinuous circles, each circle being adjacent to one of the six slits in the apertures 17, 18, the length and phase position of the slots being such that, considering one cycle of revolution of the discs 27, 28 as consisting of eight equal time intervals, the wanted radiation is allowed through by corresponding slits for two of the four intervals in the second half-cycle, whereas for each entrance slit the unwanted radiation passes through an exit slit for one interval in each half-cycle, except for one pair of non-corresponding slits, when the unwanted radiation is completely blocked for the whole cycle. The radiation passing through the exit slits is detected at 26, then amplified and rectified at 31 in synchronism with the rotating discs 27, 28 by a photo-cell 37 energized in half-cycles by the light from a lamp 36 which is intermittently blocked by a chopping disc 34, whereby the equal responses of unwanted radiation in the two half-cycles are balanced out, and the output current to the recorder is a measure of the wanted radiation reaching the detector. The entrance and exit slits may be omitted by making the slots in the rotating discs sufficiently narrow. The slots in the discs may be formed by coating the discs with a material opaque to the light to be analysed, and removed where the slots are required, or the discs may be made of reflecting material and covered with a non-reflecting surface except where the slots are required. The slots may be other than six in number, and may be other than at equal distances apart.