1、BRITISH STANDARD BS 7012-12: 1997 ISO 8576: 1996 Light microscopes Part 12: Reference system of polarized light microscopy ICS 37.020BS 7012-12:1997 This British Standard, having been prepared under the direction of the Sector Board for Materials and Chemicals, was published under the authority of t
2、he Standards Board and comes into effect on 15 April1997 BSI12-1998 ISBN 0 580 27253 2 National foreword This part of BS 7012 has been prepared by Technical Committee LBI/33 Microscopes. It is identical with ISO8576:1996 Optics and optical instruments Microscopes Reference system of polarized light
3、microscopy published by the International Organization for Standardization (ISO). A list of organizations represented on this committee can be obtained on request. Cross-references The British Standards which implement international or European publications referred to in this document may be found
4、in the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are
5、responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, the ISO title page, page ii, pages 1 to 5 and a back cover. This standard has been u
6、pdated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date CommentsBS 7012-12:1997 ii Foreword ISO (the International Organization for Standardization) is a worldwide
7、 federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that
8、committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by t
9、he technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard ISO8576 was prepared by Technical Committee ISO/TC 172, Optics and optical instruments, subc
10、ommittee SC5, Microscopes and endoscopes. Descriptors: Optics, optical equipment, microscopes, optical microscopes, displacement, rotation, coordination.BS 7012-12:1997 BSI 1998 1 1 Scope This International Standard establishes a reference system incorporating all calibrated motions of rotation and
11、displacement on the microscope and its accessories so that the measuring procedures are uniform. Particular attention is given to the polarization parameters and measuring accessories such as rotary microscope stages, polarizing devices, and compensators. 2 Principles The optical properties of an an
12、isotropic, non-absorbing crystal of minimum symmetry under constant conditions of pressure, temperature and wavelength are described by a triaxial index ellipsoid. The lengths of the semi-axes are given by the principal refractive indices n aand n band n gof the crystal. A random plane through the i
13、ndex ellipsoid containing the centre of the ellipsoid generally has the shape of an ellipse with the axes of length n a9and n g9 . By definition, the relationship n aFigure 1BS 7012-12:1997 2 BSI 1998 3.2 Mechanical stage (see Figure 2) The mechanical stage is attached to the rotary microscope stage
14、 in order to move the object in coordinate directions x and y. In the zero rotation position of the microscope stage, the positive x-direction of the mechanical stage and the reference direction are thereby identical (m = 0). 3.3 Rotation position of the microscope stage The rotation position is zer
15、o when the x-direction of the mechanical stage is west-east, i.e. parallel to the vibration direction of light supplied by the polarizer, the latter being in v = 0 (see 4.2). NOTEIf any direction other than west-east (m = 0) is taken as the basis orientation of the polarizer, then it should be indic
16、ated on the microscope. 3.4 Rotation and tilting directions of the universal stage (seeFigure 3 andFigure 4) The universal stage is a device attached to the microscope stage, with which the object is turned towards any spatial direction. It has a system of rotary and tilting axes, specified by subsc
17、ripts (according to Berek), as A n , where n =1,2,3. The highest number specifies the rotation axis of the microscope stage. Odd numbers refer to axes which, in the zero position of the universal stage, are vertical, even numbers to axes which are horizontal. The movement of one axis changes the pos
18、ition of all axes with a smaller subscript number. In the zero rotation position of the microscope stage, the scales for reading the tilting positions of the axes A 2and A 4are towards the right side of the observer so that the directions of the axes are defined as180. The working direction of A 2is
19、 mostly perpendicular to the direction of A 4 , i.e. 90. When the universal stage is tilted around A 4 , the direction 90 is that of the projection of A 2 . Seen in the directions of A 2and A 4 , the tilting angles around A 2and A 4are defined as clockwise positive, starting at the horizontal positi
20、on of the surface of the universal stage. NOTEThe following designations of the axes of the universal stage are also used: Figure 2 Berek (1924) Nikitin-Duparc-Reinhardt Reinhardt (1931) R.C. Emmons A 1 N (normal axis) N (normal axis) I.V. A 2 H (horizontal axis) H (horizontal axis) N.S. A 3 M (mobi
21、le axis) A (auxiliary axis) O.V. A 4 I (immobile axis) K (control axis) O.E.W. A 5 M (microscope axis) MBS 7012-12:1997 BSI 1998 3 4 Adjusting the polarizing devices, optically anisotropic objects, compensators and auxiliary objects 1) 4.1 Terminology The polarizing devices transmit linearly polariz
22、ed light of one vibration direction which is identical with the transmission direction of the device. Viewed in the direction of light propagation, the device in front of the object on the microscope stage is called a polarizer, and the one after the object is called an analyser. The latter is used
23、to diagnose the stage of polarization produced by the object or by the combination of object and compensator. Optically anisotropic objects are substances whose refractive indices vary with the direction of propagation and vibration of light. Compensators and auxiliary objects are devices made of op
24、tically anisotropic materials; they serve to systematically increase or decrease path differences of polarized light waves. In this way the auxiliary objects exhibit the sign of the differences in the object under examination, the compensators indicate the magnitudes of differences. 4.2 Adjusting th
25、e polarizer and the analyser (seeFigure 5) The transmission directions of both the polarizer and the analyser are referred to the zero direction west-east (m = 0). In the counter-clockwise system of the microscope stage, the rotation angles of the polarizer and analyser are positive in counter-clock
26、wise direction. The normal working rotation positions are as shown in Figure 5. 4.3 Adjusting the optically anisotropic object on the microscope stage (seeFigure 6 and Figure 7) The extinction position is reached when the directions of the refractive indices n a9and n g9 , of the object lie in paral
27、lel with the transmission directions of the crossed polarizer and analyser. The diagonal (or measuring) position is reached when the directions n a9 , and n g9 , are diagonal (at45) to the transmission directions. Figure 3 Figure 4 1) The designations “auxiliary objects”, “auxiliary specimens”, “qua
28、litative compensators” and “fixed compensators” are used synonymously in everyday language. Figure 5BS 7012-12:1997 4 BSI 1998 4.4 Adjusting the auxiliary objects and tilting compensators (seeFigure 8) The auxiliary objects and compensators are inserted in the standardized tube slots. In this case t
29、he direction of the higher refractive indices of the compensators (see note in clause 2) forms a 45 angle with the reference direction. The direction of n g9of the object on the microscope stage is then adjusted to the 135 (parallel to the n adirection of the compensator), i.e. the subtraction posit
30、ion. Exceptions exist with certain compensators after Berek or Ehringhaus, where the n gdirection of the compensator is set at the 135 position. 4.5 Adjusting the elliptic compensator after Brace-Khler (seeFigure 9) The elliptic compensator after Brace-Khler is an azimuthally rotatable anisotropic p
31、late with a known path difference cup to l/10. The rotation position of this plate is adjusted so that the n g , direction is90, i.e. parallel with the transmission direction of the analyser At the beginning of the measuring procedure the n g9direction of the object on the microscope stage is adjust
32、ed to the45 position. Then the compensator is rotated in a counter-clockwise direction until the object is extinguished. The rotation angle is b. The path difference of the object is calculated from the equation: = csin 2b. Figure 6 Figure 7 Figure 8 Figure 9BS 7012-12:1997 BSI 1998 5 4.6 De Snarmon
33、t compensation (seeFigure 10) De Snarmont compensation is achieved with a l/4 plate adjusted to the wavelength of the monochromatic light used, which transforms the elliptical vibration emanating from the object into a linear vibration of distinct direction. The angle between this vibration directio
34、n and the transmission direction of the analyser is equal to half the phase difference which is the origin of the said elliptical polarization. At the beginning of the measuring procedure the n g9direction of the object on the microscope stage is adjusted at the 45 position. Then l/4 is inserted in
35、the standardized tube slot, its n gdirection being parallel with the transmission direction of the polarizer. The analyser is rotated in the counterclockwise direction until the object is extinguished. The path difference , in nanometers, of the object is calculated from the equation: where The rang
36、e of path differences measured with de Snarmont compensation should be restricted to0 l. Dw l 180 - = l is the wavelength of the light, in nanometers, used for the measurement; Dw is the rotation angle in degrees. Figure 10BSI 389 Chiswick High Road London W4 4AL | | | | | | | | | | | | | | | | | |
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