GB710495A - Improvements in or relating to microscopy - Google Patents

Abstract

710,495. Microscopes: SMITH, F. H., and BAKER of HOLBORN, Ltd., C. Feb. 21, 1952 [Feb. 22, 1951], No. 4363/51. Addition to 639,014. Class 97(1) A microscope according to the parent Specification which embodies reflecting means to reflect two distinguishable beams back through a transparent object is modified for use with opaque specularly reflecting objects by the omission of the said reflecting means, the beam combining means comprising at least one anisotropic double-reflecting member, polarizing means being provided to cause the two distinguishable beams to be differently polarized and means to bring the beams into parallel plane polarized relationship after they leave the combining means, the two beams both being reflected back through the system 'by the object or are so reflected by the object and the other by a reflector adjacent the object. As shown in Fig. 1 a beam 16 is incident upon a vertical illuminator. plate 15 and is either plane polarized thereby or by other means. The polarized beam 18 falls on a lens system comprising a birefringent doublet 12, combined with a glass doublet 13 providing correction for spherical aberration. The lens 12 is so arranged that its internal surface 33 is in the rear focal plane of the objective 11, and produces two beams 23, 24, polarized on rightangles which are focused by the objective 11 on the object 27 at spaced points. A quarter-wave plate 14 is placed in the beams so that on their return by reflection at the object their relative polarization is such that they can be combined by the lens 12 and directed upon coincident paths to produce interference effects at the interface 33 and which will be visible in the image seen in the eyepiece. When the back focal plane of objective is within its optical train the latter may include doubly refracting elements to act as beam combining means, or a Bertrand lens provided to project an image of this plane on to the beam combining means. The lens 12 may be replaced by a doubly refracting plate placed in the convergent beam between the objective 11 and the object 27 and a quarter-wave plate or other polarizing member used to effect the interchange of the plane of polarization of the two beams. The beam combining means may be a double-refracting prism, in which case the quarter-wave plate 14 is omitted. Separate dividing and combining means may be employed. In the modification shown in Fig. 2 the two beams are produced by a semi-transparent reflector 42, adjacent the object surface 27 which is illuminated by elliptically polarized light produced by the vertical illuminator 15, double-refracting lens 12 and quarter-wave plate 14. The beam 44 reflected by the surface 42 is rendered plane polarized by the plate 14 while the transmitted beam 45 passes through a quarter-wave plate 46 and is reflected back through the plates 46 and 14 to reach the lens 12 as plane-polarized so as to be capable of combination by the lens 12 with the beam 44 to produce interference effects. Specification 710,490 also is referred to.