GB1298658A - Photometer for measuring total radiant energy at selected angles - Google Patents

Abstract

1298658 Photo-electric photo-meters BECKMAN INSTRUMENTS Inc 19 April 1971 [29 Jan 1970 21 Dec 1970] 20411/71 Heading G1A [Also in Division G2] In a photo-meter in which a laser beam 7 is focused at a point 16 in a test sample 14 and scattered light, after passage through a radiant energy mask 24, is focused on to the aperture 34 of a diaphragm 32 to be received by a detecting system 38, 40, the mask 24 has an annular aperture 26 which selects only that radiation scattered within a predetermined incremental angle #α. Alternatively, the mask 24 may be rotatable and contain a sector only of a full annulus. As shown, the incident beam is further limited by an apertured diaphragm 9, and undeviated radiation leaving the sample is either absorbed or reflected away by a trap 20. The detector 40 may be a photo-multiplier, photo-diode or phototube provided with calibrated attenuators 44, 45 and a filter 38, and the lens 28 may be replaced by a concave mirror or fibre optics. A mirror 47 can be placed in the optical path to enable visual observation or photographic recording of the scattered light pattern. Alternatively a telescope can be placed between the lens 28 and mask 32 for visual observation. The apparatus is used to determine the scattering or fluorescing properties of a suspension 14 placed in a transparent walled test cell 10, or of a solid, e.g. a photographic film. By using a polarizer 21 and analyser 46 the state of polarisation of the scattered light may be investigated. A measurement of the radiation transmitted through the sample is made by removing the trap 20, the device 25 being an attenuator provided for safety reasons. Wide-angle scattering is monitored either by surrounding the test cell with an annular mirror (52), Fig. 2 (not shown), or by having an additional collecting lens (27) immediately downstream of the test cell, Fig.3 (not shown). Light scattered to one side only of the sample can also be monitored, Fig. 4 (not shown), as can back-scattered radiation, Fig. 5 (not shown), by using plane mirror arrangements to irradiate the sample at the required angle. A number of masks 24 having different aperture sizes may be mounted on a rotatable or slidable holder for investigating scattering effects at different angles, and the apertures in diaphragms 9 and 32 may be adjusted in a similar manner. The apparatus may be used in a dual beam device, the other beam being the conventional reference beam.