Patent GB-772073-A (GB)
Title: Interferometer
IPC: G01N21/45
Filed: 1955-05-05
Abstract: 772,073. Interferometer. ZEISS-STIFTUNG, C., [trading as ZEISS, C. [Firm of]]. May 5, 1955 [May 20, 1954], No. 13117/55. Class 97(1) An interferometer, especially adapted for finding the distribution of refractive index in stratified solutions is characterized in that it consists of a beam-splitting prism, a plane mirror, and a pair of mutually perpendicular reflectors, so arranged that the rays reflected in the beam-splitting prism as well as the beams transmitted through the prism are reflected on to the plane mirror and the pair of reflectors, and pass round the interferometer in opposite directions. As shown in Fig. 1, a beamsplitting prism 1 has a semi-transparent reflecting layer 1<SP>1</SP>, so that a beam of light 8 entering the prism is split into two parts 6, 7. A pair of mutually perpendicular reflecting surfaces 2, 3 are placed in the path of the transmitted beam 7 with its ridge surface 2<SP>1</SP> in the plane of the reflected and transmitted beams. The transmitted beam 7 falls on one of the reflecting surfaces at 13, is reflected to the other reflecting surface at 14; and is thence reflected to a plane mirror 5, from which it is reflected back to the beam-splitting prism 1. The reflected beam 6 is reflected first at the plane mirror 5, thence at 16, 17 at the reflecting surfaces of the dihedral 2, and thence back to the beam-splitting prism 1. A cell 9 containing the solution under test is placed by the side of a second cell 10 (not shown) containing a comparison solution between the dihedral reflector 2 and the plane mirror 5. Owing to the invertion of the beams at the reflectors 2, 3, the rays passing through the two cells are combined and are viewed on emergence from a beam-splitting prism 1, an image of the interference pattern being formed on a screen by a projection system, if desired. A pair of plane-parallel plates 11 may be placed between the beam-splitting prism 1 and the dihedral reflectors 2, 3 so as to be rotatable about an axis 12, so that the interval between the interfenence bands may be adjusted. Alternatively, the cells 9, 10 may be formed as plane-parallel plates which may be rotatable. The reflectors 2, 3 in this instance preferably form a roof prism. The cells 9, 10 may be replaced by a single cell with a removable partition. The cell is filled with the solution under test on one side of the partition, and with a comparison solution on the other side. When the partition is removed, the solutions mix, and the effect of the mixing on the refractive index can be .observed. In a modification, Fig. 4, the reflecting surfaces consist of plane mirrors 30 meeting in a common line 40. Since the operative parts of the reflecting surfaces are spaced apart, those parts thereof in the region of the line 40 may be omitted. A beamsplitting prism 1 and a plane reflector 5 are provided as before, and the central portions of these elements may also be omitted. The cells 34, 35 for the solutions are mounted on a rotatable shaft 36, concentric with a disc 39 having diametrically opposite apertures. Disc 39 rotates at half the speed of the cells 34, 35, so that light is allowed to pass through the cells and through the apertures only in one position of the cells. In a modification shown in Fig. 6, the reflectors 2, 3 have their ridge 2<SP>1</SP> perpendicular to the plane containing the principle transmitted and reflected rays. This results in an inversion of the reflected beam with respect to the transmitted beam, as indicated by the arrows 51<SP>1</SP>, 50, 51<SP>11</SP>. In this case, no comparison solution is required, and the cell 50 containing the solutions under test may be rotated if desired. In all modifications, polarization is liable to occur on reflection. This may be obviated by using metallized reflecting surfaces, or by inserting an analyser in the observation beam of the interferometer.