GB701110A - An optical system for use in the examination of opaque objects by interferometry - Google Patents

Abstract

701,110. Microscopes. ASSOCIATED ELECTRICAL INDUSTRIES, Ltd. Nov. 16, 1951 [Nov. 23, 1950; Feb. 9, 1951], Nos. 28693/50 and 3242/51. Class 97(1) A system for use between a microscope objective and the object comprises an axial alignment from the objective or plane surface totally reflecting towards the object, a plane semi-reflecting surface and a curved reflecting surface with a central aperture, an illuminating beam being reflected by the curved surface to the semi-reflecting surface by which it is divided into two portions, a reflected portion which passes through the said central aperture and is reflected by the object to be combined with the second transmitted portion reflected back by the totally reflecting plane surface, interference effects being visible in the combined beams. As shown in Fig. 1 accompanying first Provisional Specification the system comprises a plane-parallel glass plate 1 having a semi-reflecting surface 2 and a fully reflecting area 3 on the other surface. A glass plate 6, placed upon the plate 1 with an oil layer intervening has a small mirror 7 reflecting a divergent beam 8 on to the fully reflecting curved surface of a plano-convex lens 4 cemented to the plate 2 and connected by an oil layer to the opaque object 5. This light is reflected upwardly by the reflecting surface of the lens and part is focused thereby on the reflecting area 3 while part is reflected by the semi-reflecting surface 2 to be focused upon the object through a central aperture in the reflecting surface of the lens 4. Light reflected from the area 3 is again partly reflected by the surface 2 to form a beam which can interfere with that reflected by the object 5. These beams are diverted upwardly to a transparent plate 9 to be reflected downwardly by a spherical reflecting surface 10 thereof on to a further semi-transparent reflecting surface 11 whence they are again reflected to form an image of the object at a central aperture on the reflecting surface 10 which image is viewed by means of the microscope objective 12. The interfering effects may be varied by changing the spacing of the object and plate 1. In a modification the plate 6 is omitted and the plate 1 has a side edge in, the shape of the frustum of a sphere through which a convergent beam of light is diverted to be reflected upwardly on to the semireflecting surface 2 by a convex mirror carried by a plate located between the plate 1 and the object 5 and having a central aperture through which the latter is illuminated. Further where an objective having a long working distance is employed the plate 9 may be omitted. In the modification shown in the drawing accompanying the complete Specification the semi-reflecting surface 2 is located between two glass members 1, 4 each having a fully reflecting curved surface, the reflecting surface 17 of member 1 having a plane central area carrying the total reflecting area 3 and having' a glass block 19 cemented thereto. Illumination is reflected by a mirror 23 into the objective 12 by a beam 25 focused on mirror 23, and is directed through the objective 12 into plate 19. Part is focused on the reflector 3 by the lower reflecting surface and part focused on the. object 5 after reflection at the surface 2. Light reflected by the reflector 3 passes through the surface 2 and is focused by the lower reflector on the point 20 at which also an image of the object is formed by light reflected thereby and by the surface 2. The image is viewed in the microscope. An image of the surface 5 is formed at the point 21 by the reflecting surface 17 and the semi-reflector 2, and an image of this image is focused by the objective 12 at the mirror 23. Thus the object is properly illuminated by the beam 25. In a further modification the member 1 is replaced by a plane parallel glass plate bearing the reflector 3, and an ordinary vertical illuminator employed in the microscope. Specifications 651,035 and 676,749 are referred to.