1、BRITISH STANDARD BS ISO 11455:1995 Implementation of ISO11455:1995 Raw optical glass Determination of birefringenceBSISO11455:1995 This BritishStandard, having been prepared under the directionof the Consumer Products and Services Sector Board, was published under theauthority of the StandardsBoard
2、and comesinto effect on 15June1995 BSI02-2000 The following BSI references relate to the work on this standard: Committee reference CPW/172 Draft for comment93/301950 DC ISBN 0 580 24358 3 Committees responsible for this BritishStandard The preparation of this BritishStandard was entrusted to Techni
3、cal Committee CPW/172, Fundamental aspects of optical standards, upon which the following bodies were represented: AEA Technology British College of Optometrists British Measurement and Testing Association Department of Trade and Industry (Eureka643) Department of Trade and Industry (National Physic
4、al Laboratory) Engineering Equipment and Materials Users Association Flat Glass Manufacturers Association Institute of Physics Ministry of Defence Sira Limited Society of British Aerospace Companies Limited Amendments issued since publication Amd. No. Date CommentsBSISO11455:1995 BSI 02-2000 i Conte
5、nts Page Committees responsible Inside front cover National foreword ii Foreword iii Text of ISO11455 1BSISO11455:1995 ii BSI 02-2000 National foreword This BritishStandard reproduces verbatim ISO11455:1995 and implements it as the UK national standard. This BritishStandard is published under the di
6、rection of the Consumer Products and Services Sector Board whose Technical Committee CPW/172 has the responsibility to: aid enquirers to understand the text; present to the responsible international committee any enquiries on interpretation, or proposals for change, and keep UK interests informed; m
7、onitor related international and European developments and promulgate them in the UK. NOTEInternational and European Standards, as well as overseas standards, are available from Customer Services, BSI,389 Chiswick High Road, London W44AL. A British Standard does not purport to include all the necess
8、ary provisions of a contract. Users of British Standards are 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, pagesi andii, theISO ti
9、tle page, pagesii toiv, pages1 to6 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.ISO11455:1995(E) ii BSI 02-2000 Contents Page Foreword iii Introduction 1 1 Scope
10、 1 2 Definition 1 3 Principle 1 4 Apparatus 1 5 Test samples 3 6 Procedure 3 7 Expression of results 4 8 Test report 5 Annex A (informative) Bibliography 6 Figure 1 Principal stresses shown in a rectangular plate 2 Figure 2 Test arrangement as described by de Snarmont and Friedel, including the spec
11、imen 3 Figure 3 Examples of test samples, including possible measuring points 4ISO11455:1995(E) BSI 02-2000 iii Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards
12、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 committee. International organizations, governmental and non-governmental, in liaison with ISO, also take pa
13、rt in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Stan
14、dard requires approval by at least75% of the member bodies casting a vote. International Standard ISO11455 was prepared by Technical Committee ISO/TC172, Optics and optical instruments, Subcommittee SC3, Optical materials and components. Annex A of this International Standard is for information only
15、.iv blankISO11455:1995(E) BSI 02-2000 1 Introduction Raw optical glass in bulk and preshaped forms may have permanent stress caused by the manufacturing procedure or temporary stress caused by thermal or mechanical load. These stresses cause anisotropy of the refractive index which causes path diffe
16、rences of the light path in the given object (in centimetres) which are measurable by interference optics. The birefringence, in nanometres per centimetre, is valid for the glass piece when isothermal and not mechanically altered and is the integrated value for the resultant wavefront deformation ca
17、used by an anisotropy of the refractive index. 1 Scope This International Standard describes the stress optical method for determining the birefringence in glass, especially in raw optical glass in bulk and pre-shaped forms. This method is also used in photoelasticity. NOTE 1The calculation of the e
18、lastomechanical stress from the birefringence is not the subject of this International Standard. NOTE 2The indication on the drawings of birefringence is specified in ISO10110-2 (see reference2 in Annex A). This test method is applicable for simple geometrical shapes of glass (see clause5). 2 Defini
19、tion For the purposes of this International Standard, the following definition applies. 2.1 birefringence (of glass) an anisotropy of refractive index in optically homogeneous and isotropic glasses, usually induced by mechanical and/or thermal stress. The refractive index depends on the orientation
20、of the plane of polarization and the propagation vector of the electromagnetic wave with respect to the axis of the principal stresses Definition taken from ISO9802. 3 Principle Measurement of the optical path differences by compensation using an optical interference method with polarized light. In
21、the compensation procedure described by de Snarmont and Friedel a phase retardation of one wavelength is produced by a rotation of180 in a linear function, using light of wavelength near maximum of sensitivity of human eye (i.e.546nm to589nm). If an optically isotropic glass body under stress is irr
22、adiated with polarized light in the direction of one principal stress (such as 3 , see Figure 1), the oscillating components in the direction of principal stress, 1and 2 , show a different speed of propagation related to the value in a stress-free glass body. The refractive indices n 1and n 2are rel
23、ated to the principal stresses 1 , 2and 3by: From equations(1) and(2), equation(3) for the difference in refractive index may be obtained: The difference in refractive index (n 1 n 2 ) is the birefringence %n, which is related to the stress optical coefficient K = p q at the wavelength used as follo
24、ws: For the correlation between birefringence, %n, and the optical path difference, %s, between the wave components in the principal stress direction, 1and 2 , after passing through the sample thickness a (which is usually equal to light patha), the following equation may be applied: The birefringen
25、ce %n is given in nanometres per centimetre. 4 Apparatus 4.1 Instrument for measuring the thickness of the specimen at the measuring points to1% e.g.callipers. 4.2 Polarimeter with a compensator as described by de Snarmont and Friedel. 4.2.1 Polarimeter components The polarimeter shall consist of th
26、e following components (see also Figure 2). a) Source of collimated light, e.g.white light source with monochromatic filter for a wavelength of546nm or589nm. b) Diffuser, e.g.an opal glass or a uniformly ground glass screen. . . . (1) . . . (2) where n 0 is the refractive index of the unstressed gla
27、ss; p and q are related to the type of glass. . . . (3) . . . (4) . . . (5)ISO11455:1995(E) 2 BSI 02-2000 c) Polarizer, containing a cross-section line at45 to the polarizing direction. The polarizer is mounted between glass and housed in a rotatable mount capable of being locked in a fixed position
28、. d) Specimen holder. e) Quarter-wave plate, having a retardation equivalent to one quarter of the wavelength of the light being used. It shall be housed in a rotatable mount capable of being locked in a fixed position. f) Analyser, identical to the polarizer. It shall be housed in a rotatable mount
29、 capable of being locked in a fixed position. This mount shall then be housed within a graduated mount capable of being rotated 180 . In addition, the following components may be used: g) Full-wave plate, having a retardation of565nm which produces, with white light, a violet-red colour. It shall be
30、 housed in a rotatable mount capable of being locked in a fixed position. h) Telescope, i.e.a short-focus telescope having a suitable magnifying power over the usable focusing range in case of parallax-free light passing close to the edge of the glass body. i) Immersion cell, non-birefringent, for t
31、esting samples and optical elements having non-parallel or unpolished surfaces. The immersion cell shall contain a non-birefringent fluid which closely matches the index of refraction of the specimen glass. It is possible to build up a reversed set de Snarmont compensator with the light source at th
32、e position of the viewer (see Figure 2) and the viewer looking at the polarizer. 4.2.2 Adjustment of the polarimeter The polarimeter shall be adjusted so that the45 line on the polarizer is parallel to the edge of the sample. The analyser shall be rotated without the full-wave plate and the quarter-
33、wave plate to zero-position to produce homogeneous darkness. Finally, the quarter-wave plate shall be adjusted to maximum darkness through rotation and fixed in position. In case of using a full-wave plate to help in determination of tensile or compressive stress at the edge, the full-wave plate sha
34、ll be adjusted to maximum darkness in the case of monochromatic light. Switch to a white light source with the full-wave plate interference-colour red-violet (“first order red”). The sensitivity in compensating of very little brightening, caused by small birefringence, or small path length, in the g
35、lass body depends on the surface polishing and on the quality of polarizer, analyser and quarter-wave plate. Best results are obtained only with parallax-free long distance optics using the short-focus telescope. Figure 1 Principal stresses shown in a rectangular plateISO11455:1995(E) BSI 02-2000 3
36、5 Test samples The test samples should be of simple geometrical shapes, e.g.rotationally symmetrical, rectangularly cut plates and blocks, and equilateral, rectangular triangles. The test samples should have two opposite planeparallel polished surfaces. For these test samples, apply the normal test
37、procedure. In case of test samples with non-planeparallel and/or unpolished surfaces, use the immersion cell see4.2.1 i). Examples of test samples with polished surfaces and measuring points are given in Figure 3. The test samples shall be held in isothermal conditions at room temperature to reach a
38、n equilibrium temperature before and during measurement. 6 Procedure 6.1 Place the test sample so that the principal stress direction lies at45 to the oscillating plane of the light. In this way, the oscillating components in the direction of the principal stresses 1and 2have the same amplitude but
39、a different optical path length, %s, when leaving the test sample (elliptical polarized light). The point of birefringence measurement shall be close to the edge of the test sample, at a distance of approximately5% of the diameter of the width from the edge. 6.2 The tangent plane at the measuring po
40、int for round test samples shall lie at45 to the polarizer. For rectangular cross-sections and right-angled triangular cross-sections, the point of measurement shall be as shown in Figure 3. 6.3 Determine the light path by measuring the thickness of the test sample at the measuring point to1%. Figur
41、e 2 Test arrangement as described by de Snarmont and Friedel, including the specimenISO11455:1995(E) 4 BSI 02-2000 6.4 Rotate the analyser until the path difference is compensated, this means until the maximum darkness has occurred at the selected point of measurement. During passage through the qua
42、rter-wave plates, linearly polarized light is produced, whose plane of oscillation is rotated relative to the original plane of the polarizer by an angle proportional to the optical path difference. Note the angle at this position. The sign of the angle() depends on the sense (compression or tension
43、) of the principal stress difference (see6.5). Repeat the measurement for further measuring points (Figure 3). 6.5 For information on the sign of the stress close to the edge of the test sample, switch to the white light source by taking out the monochromatic filter and putting in the full-wave plat
44、e. Colourless brightening caused by minor path differences (smaller than half wavelength) appear in the well-known sequence of white light interference colours from red-violet to blue or yellow in the other direction. The determination of tension or compression can be made by comparison to single-ax
45、is prestressed rods or test discs. Using the full-wave plate, the analyser shall be in zero-position. NOTE 3The change of colour depends on the orientation of the principal stress cross in the test sample to the polarizing direction. NOTE 4For glasses with negative stress optical coefficients (for i
46、nstance glasses with a mass fraction of PbO of more than75%), interference colours will be reversed from the stress correlate determined with prestressed rods or test discs of glass with positive (normal) stress optical coefficients. Another way to determine the sign of the stress is to introduce a
47、point-like force on the test specimen leading to regions of known stress orientations. 6.6 The compensation range given by the procedure described by de Snarmont and Friedel is limited to a maximum retardation of one wavelength(180 ). If the path-difference exceeds one wavelength, the interference l
48、ines shall be counted starting with the neutral black line as zero which has to be determined previously with the white light source (without the monochromatic filter). The visible region beyond the highest coloured line (after switching to monochromatic light, it is a black line) shall be compensat
49、ed in accordance with6.4 and shall be added to the already counted wavelengths. 7 Expression of results For each measuring point, calculate the birefringence according to the following equation: Figure 3 Examples of test samples, including possible measuring points . . . (6) where %n is the birefringence, in nanometres per centimetre; %s is the optical path difference, in nanometres; a is the light path (sample thickness), in centimetres; is the rotation of the analyser required to produce darkness at t
