1、 Reference number ISO/TR 14999-2:2005(E) ISO 2005TECHNICAL REPORT ISO/TR 14999-2 First edition 2005-03-01 Optics and photonics Interferometric measurement of optical elements and optical systems Part 2: Measurement and evaluation techniques Optique et photonique Mesurage interfromtrique de composant
2、s et systmes optiques Partie 2: Mesurage et techniques dvaluation ISO/TR 14999-2:2005(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are lic
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6、permission in writing from either ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2005 All rights
7、reservedISO/TR 14999-2:2005(E) ISO 2005 All rights reserved iiiContents Page Foreword iv Introduction v 1 Scope 1 2 Measurement objects . 1 2.1 Surfaces . 1 2.2 Optical components in transmission 2 2.3 Optical systems. 3 2.4 Indirect examination of the function of optical elements . 3 3 Hardware asp
8、ects of an interferometer and test environment. 4 3.1 General. 4 3.2 Construction principles and influences on the quality of measurements 5 3.3 Test environment 15 4 Methods for evaluating the optical path difference. 18 4.1 General. 18 4.2 Visual inspection of interferograms 18 4.3 Manual evaluati
9、on of interferograms 24 4.4 Phase measurements with temporal carrier 26 4.5 Phase measurements with spatial carrier 32 4.6 Removal of phase ambiguities (phase unwrapping). 34 4.7 Registration of wavefronts; coordinate systems, coordinate system definition . 35 4.8 Polynomial and other representation
10、s of wavefronts. 36 5 Test reports and calibration certificates. 38 5.1 General. 38 5.2 Content of test reports and calibration certificates 39 5.3 Test reports . 39 5.4 Calibration certificates . 39 5.5 Opinions and interpretations. 40 5.6 Electronic transmission of results 40 5.7 Format of reports
11、 and certificates. 40 5.8 Amendments to test reports and calibration certificates . 41 6 Data format 41 Annex A (informative) Orthogonal polynomials 42 Annex B (informative) Orthogonal functions on “unusual areas” 56 Bibliography . 59 ISO/TR 14999-2:2005(E) iv ISO 2005 All rights reservedForeword IS
12、O (the International Organization for Standardization) is a worldwide 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 co
13、mmittee has been established has the right to be represented on that 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 electro
14、technical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the me
15、mber bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. In exceptional circumstances, when a technical committee has collected data of a different kind from that which is normally published as an International Standard
16、(“state of the art”, for example), it may decide by a simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely informative in nature and does not have to be reviewed until the data it provides are considered to be no longer valid or useful. Atte
17、ntion is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO/TR 14999-2 was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee SC 1, F
18、undamental standards. ISO 14999 consists of the following parts, under the general title Optics and photonics Interferometric measurement of optical elements and optical systems: Part 1: Terms, definitions and fundamental relationships (Technical Report) Part 2: Measurement and evaluation techniques
19、 (Technical Report) Part 3: Calibration and validation of interferometric test equipment (Technical Report) Part 4: Interpretation and evaluation of tolerances specified by ISO 10110 ISO/TR 14999-2:2005(E) ISO 2005 All rights reserved vIntroduction A series of International Standards on Indications
20、in technical drawings for the representation of optical elements and optical systems has been prepared by ISO/TC 172/SC 1, and published as ISO 10110 under the title Optics and photonics Preparation of drawings for optical elements and systems. When drafting this standards series and especially its
21、Part 5, Surface form tolerances and Part 14, Wavefront deformation tolerance, it became evident to the experts involved that additional complementary documentation is required to describe how the necessary information on the conformance of the fabricated parts with the stated tolerances can be demon
22、strated. Therefore, the responsible ISO Committee ISO/TC 172/SC 1 decided to prepare an ISO Technical Report on Interferometric measurement of optical wavefronts and surface form of optical elements. When discussing the topics which had to be included into or excluded from such a Technical Report, i
23、t was envisaged that it might be the first time, where an ISO Technical Report or Standard is prepared which deals with wave-optics, i.e. that is based more in the field of physical optics than in the field of geometrical optics. As a consequence only fewer references than usual were available, whic
24、h made the task more difficult. Envisaging the situation, that the topic of interferometry has so far been left blank in ISO, it was the natural wish to now be as comprehensive as possible. Therefore there was discussion, whether important techniques such as interference microscopy (for characterizi
25、ng the micro-roughness of optical parts), shearing interferometry (e.g. for characterizing corrected optical systems), multiple beam interferometry, coherence sensing techniques or phase conjugation techniques should be included or not. Other techniques, which are related to the classical two beam i
26、nterferometry, like holographic interferometry, Moir techniques and profilometry were also mentioned as well as Fourier transform spectroscopy or the polarization techniques, which are mainly for microscopic interferometry. In order to complement ISO 10110 the guideline adopted was to include what p
27、resently are common techniques used for the purpose of characterizing the quality of optical parts. Decision was made to complete a first Technical Report, and to then up-date it by supplementing new parts, as required. It is very likely that more material will be added in the near future as more st
28、ringent tolerances (two orders of magnitude) for optical parts and optical systems become mandatory when dealing with optics for the EUV range (wavelength range 6 nm to 13 nm) for microlithography. Also, testing optics with EUV radiation (the same wavelength as they are later used, e.g. at-wavelengt
29、h testing) can be a new challenge, and is not covered by any current standards. This part of ISO 14999 should cover the need for qualifying optical parts and complete systems regarding the wavefront error produced by them. Such errors have a distribution over the spatial frequency scale; in this par
30、t of ISO 14999 only the low- and mid-frequency parts of this error-spectrum are covered, not the very high end of the spectrum. These high-frequency errors can be measured only by microscopy, measurement of the scattered light or by non-optical probing of the surface. A similar statement can be made
31、 regarding the wavelength range of the radiation used for testing. ISO 14999 considers test methods with visible light as the typical case. In some cases, infrared radiation from CO 2 -lasers in the range of 10,6 m is used for testing rough surfaces after grinding or ultraviolet radiation from excim
32、er- lasers in the range of 193 nm or 248 nm is used for at-wavelength testing of microlithography optics. However, these are still rare cases, which are included in standards, that will not be dealt with in detail. The wavelength range outside these borders is not covered. TECHNICAL REPORT ISO/TR 14
33、999-2:2005(E) ISO 2005 All rights reserved 1Optics and photonics Interferometric measurement of optical elements and optical systems Part 2: Measurement and evaluation techniques 1 Scope This part of ISO 14999 gives fundamental explanations to interferometric measurement objects, describes hardware
34、aspects of interferometers and evaluation methods, and gives recommendations for test reports and calibration certificates. 2 Measurement objects 2.1 Surfaces 2.1.1 Mirrors: boundary surfaces of optical components in transmission A common task in interferometry is measurement of the shape of a surfa
35、ce. This can be accomplished in two different ways. Either reflected light or the light transmitted through the surface could be used for the measurement. Interferometric measurement is achieved by comparing the difference of two optical path lengths nd . Usually one path is called the reference pat
36、h, the other the measurement path. The resulting wave aberration, W, for a displacement d of the surface, if measured in reflection, is 2 Wn d = . The same displacement measured in transmission results in the wave aberration ( ) 21 Wnnd = . 2.1.2 Reflection degree The Fresnel reflection from the bou
37、ndary between two different media, R, can be calculated from the refractive index n 1and n 2at the boundary surface. 2 21 21 nn R nn = + (1) For most optical glasses this value is between 4 % and 6 %, so an average of 5 % is usually a good estimate. This reflection causes a loss of light from the tr
38、ansmitted wavefront at every surface. On the other hand, this reflection is often used for the measurement itself. To obtain maximum fringe visibility, or contrast, the two interfering beams should have approximately the same intensity. Changing the reflectivity of the beam splitter within an interf
39、erometer only changes the amount of light in the interference pattern and does not change the beam intensity ratio of the two beams because the light in both arms is transmitted through and reflected by the beam splitter once. If the measurement path and reference path are separated, as in a Mach-Ze
40、hnder or Twyman-Green set-up, it is usually possible to adjust the intensities of the light in both arms. ISO/TR 14999-2:2005(E) 2 ISO 2005 All rights reservedA major problem arises in a Fizeau interferometer. If the reference surface has high reflectance, the result will be multiple beam interferen
41、ce fringes resulting in narrow fringes as in a Fabry-Perot interferometer. If sinusoidal fringes are required as for the evaluation by phase shift interferometry, the reference surface shall have low reflection and an element has to be introduced between the reference and the measurement surface tha
42、t will absorb light without distorting the wave aberration. 2.1.3 Roughness For interferometric measurement the roughness of the measured surface should not exceed a certain limit that is a fraction of the wavelength and of the difference of indices of refraction, if used in transmission. 2.1.4 Topo
43、logy of the regions Difficulties may arise with interferometer software when the wavefront area has breaks in it (e.g. because it is split into segments by the mechanical supports of the secondary mirror of a mirror telescope). Problems are most severe with static fringe analysis software that depen
44、ds strongly on using neighbouring points to determine the position and continuity of fringes. Phase shift software is not affected to the same extent as it is a point-by-point evaluation of wave aberrations. Similar problems may occur if the wavefront area has a complicated outline. 2.1.5 Continuity
45、 of the surface; gradient of the surface Due to the inherent ambiguity of n2 it is not possible to measure any arbitrary surface shape uniquely. The evaluation of a surface is usually correct, if the wave aberration between two resolvable points is less than . The gradient of the surface under test
46、relative to the reference surface results in a gradient of the measured wave aberration and in high-density or closely spaced fringes. Interferograms cannot be evaluated, if the fringe separation is less then twice the distance of two resolvable points. If this condition is not possible by adjustmen
47、t, or by changing the measurement set-up, compensating optics may be required in some cases. Some of the problems caused by the ambiguity can be solved by multiple wavelength interferometry. 2.1.6 Stiffness of mirrors; finite-element-calculations During measurement the method of supporting the optic
48、s being tested should not deform them other than when used as intended. It is sometimes difficult to notice whether an object is deformed during the measurement. As a first indication of the influence of the support, the object can be measured by supporting it in two completely different ways. In th
49、e case of any doubt, a finite-element-calculation is recommended. 2.1.7 Temperature homogeneity of mirrors During measurement the object shall have a homogeneous temperature. Inhomogeneous temperatures can cause deformations as the expansion coefficient of optical materials is rather high and the thermal conductivity is very low. Stabilization can take some minutes but may sometimes require several hours. 2.1.8 Examples of measurement objects Items that can be measured by interferometry include optical flats,
