GB676749A - Improvements relating to the microscopic examination by interferometry of transparent objects - Google Patents

Abstract

676,749. Optical apparatus. ASSOCIATED ELECTRICAL INDUSTRIES, Ltd. May 8, 1950 [June 16, 1949], No. 16118/49. Class 97 (i). In or for use in the microscopic examination by interferometry of substantially transparent objects, an optical system, included or adapted to be included between a microscope objective and a source of light, comprises four surfaces arranged in spaced substantially parallel planes, of which the three remote from the light source when in use are formed to produce partial reflection and the surface nearest the light source is formed with a small spot which is totally reflecting in the direction of the objective and is arranged on the optical axis of the microscope, the arrangement being such that with an object centred on the optical axis of the microscope and positioned between the second and third surfaces and illuminated by a light beam converging on the object from the source, a virtual image of the source is formed by light which passes through the object and another coincident virtual image of the source is formed by light which does not pass through the object. As shown, the system comprises a pair of substantially plane parallel glass plates 2, 7 of which the surfaces 3, 9 and 8 are halfsilvered and the surface 5 has a central spot 4 which is completely silvered. Between the plates is the transparent object 6, the spaces between the object and the plates being filled up with immersion oil 10. Cemented to the surface 8 of plate 7 is a glass block 12, the upper surface of which is spherically concave with its centre of curvature at 4 and is completely reflecting except at 14 on the axis of the microscope objective 15. Converging light 1 from a condenser (not shown) enters plate 2 and part thereof is reflected at surface 3 and totally reflected at 4 so that a percentage of the light passes through plate 7 without passing through object 6. The other part of the light is transmitted by surface 3 and the object 6 and a percentage thereof is reflected by surfaces 8 and 9 of plate 7 to combine with the firstmentioned part and thus produce interference effects. The combined light rays are then partly transmitted by the surface 8 and are incident normally on surface 13 whereby they are reflected again on surface 8 which directs the light through the transparent area 14 into the objective 15. The plates 2, 7 may be wedges of small angle, the wedge edges being parallel and a screw 11 is provided for moving wedge 2 so as to vary the phase difference between the light rays which combine at surface 9. Specification 651,035 is referred to.