1、BSI Standards PublicationBS ISO 13142:2015Electro-optical systems Cavity ring-down technique forhigh-reflectance measurementBS ISO 13142:2015 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 13142:2015. The UK participation in its preparation was entrusted to Te
2、chnical Committee CPW/172, Optics and Photonics.A list of organizations represented on this committee can be obtained on request to its secretary.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. The British St
3、andards Institution 2015.Published by BSI Standards Limited 2015ISBN 978 0 580 80659 9 ICS 31.260 Compliance with a British Standard cannot confer immunity from legal obligations.This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 July 2015.Am
4、endments/corrigenda issued since publicationDate T e x t a f f e c t e d ISO 2015Electro-optical systems Cavity ring-down technique for high-reflectance measurementSystmes lectro-optiques Technique dalternance de la cavit pour le mesurage du facteur de rflexionINTERNATIONAL STANDARDISO 13142First ed
5、ition 2015-07-01Reference number ISO 13142:2015(E)BS ISO 13142:2015ISO 13142:2015(E)ii ISO 2015 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2015, Published in SwitzerlandAll rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in an
6、y form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCh. de Bland
7、onnet 8 CP 401CH-1214 Vernier, Geneva, SwitzerlandTel. +41 22 749 01 11Fax +41 22 749 09 47copyrightiso.orgwww.iso.orgBS ISO 13142:2015ISO 13142:2015(E)Foreword ivIntroduction v1 Scope . 12 Normative references 13 Terms and definitions . 14 Symbols used and units of measure . 15 Test principles . 25
8、.1 General . 25.2 Decay time of initial cavity and reflectance of cavity mirrors 25.3 Decay time of test cavity and reflectance of test sample 45.4 High reflectance measurement with an optical feedback CRD technique . 46 Preparation of test sample and measurement arrangement . 66.1 Test sample . 66.
9、2 Laser source 66.3 Ring-down cavity 66.4 Detection unit . 66.5 Data acquisition and processing 76.6 Environment . 77 Test procedure 77.1 General . 77.2 Measurement of decay time of initial cavity 77.3 Calculation of reflectance of cavity mirrors . 87.4 Measurement of decay time of test cavity . 87.
10、5 Calculation of reflectance of test sample 87.6 Assessments of the measurement 88 Main error factors . 88.1 Influence of the instrumental response time on reflectance measurement 88.1.1 General 88.1.2 Multi-parameter fitting method . 98.1.3 Data truncation method 98.2 Measurement error of the refle
11、ctance of cavity mirrors .108.3 Measurement error of the reflectance of test sample 109 Test report 10Annex A (informative) Reflectance reliability check experiment .12Annex B (informative) Test report .13Bibliography .14 ISO 2015 All rights reserved iiiContents PageBS ISO 13142:2015ISO 13142:2015(E
12、)ForewordISO (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 t
13、echnical 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 part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters
14、 of electrotechnical standardization.The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of ISO documents should be noted. This docume
15、nt was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).Attention 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
16、 patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents).Any trade name used in this document is information given for the convenience of users and does
17、not constitute an endorsement.For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary informati
18、on.The committee responsible for this document is ISO/TC 172, Optics and photonics, Subcommittee SC 9, Electro-optical systems.iv ISO 2015 All rights reservedBS ISO 13142:2015ISO 13142:2015(E)IntroductionWith the development of film-deposition technology, the performance of optical thin films, espec
19、ially the highly reflective coatings which are widely used in large high-power laser systems, interferometric gravitational-wave detectors, laser gyroscopes, and cavity-enhanced and cavity ring-down spectroscopy applications, has been substantially improved in recent years. Laser-based optical syste
20、ms require some optical components with extremely high reflectance characteristic. It is necessary to be able to measure this reflectance characteristic precisely. The measurement procedures in this International Standard have been optimized to allow the measurement of high reflectance (larger than
21、99 %, theoretically up to 100 %) of optical laser components using the cavity ring-down technique which provides reflectance data with high accuracy, high repeatability and reproducibility, and high reliability. ISO 2015 All rights reserved vBS ISO 13142:2015ISO 13142:2015(E)BS ISO 13142:2015Electro
22、-optical systems Cavity ring-down technique for high-reflectance measurement1 ScopeThis International Standard specifies measurement procedures for the precise determination of the high reflectance of optical laser components. Up to now, the ISO standardized testing methods for reflectance of optica
23、l laser components have the accuracy limit of approximately 0,01 % (for measurement of absolute reflectance) which are not appropriate for measuring the reflectance higher than 99,99 % or, in some cases, measurement accuracy better than 0,01 % is required. The range of application of this standardiz
24、ed test method is reflectance 99 % and higher (theoretically up to 100 %).The methods given in this International Standard are intended to be used for the testing and characterization of high reflectance of both concave and plane mirrors used in laser systems and laser-based instruments. The reflect
25、ance of convex mirrors can also be tested by taking into consideration the radius of curvature of the mirror surface.2 Normative referencesThe following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only t
26、he edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.ISO 11145, Optics and photonics Lasers and laser-related equipment Vocabulary and symbolsISO 14644-1, Cleanrooms and associated controlled environments Part 1: Classific
27、ation of air cleanliness by particle concentration3 Terms and definitionsFor the purposes of this document, the terms and definitions given in ISO 11145 and the following apply.3.1reflectanceratio of the reflected radiant or luminous flux to the incident flux in the given conditions4 Symbols used an
28、d units of measureTable 1 Symbols used and units of measureSymbol Unit Termc m/s speed of light in measurement environmentc0m/s speed of light in vacuumh(t) impulse response of the ring-down cavityh0(t) instrumental response functionL0, L m lengths of the initial and test cavitiesL0, L m measurement
29、 errors of the initial and test cavity lengthsn refractive index of air in measurement environmentINTERNATIONAL STANDARD ISO 13142:2015(E) ISO 2015 All rights reserved 1BS ISO 13142:2015ISO 13142:2015(E)Symbol Unit TermR average reflectance of the concave cavity mirrors, equals square root of R1*R2R
30、sreflectance of the test sampleR1, R2reflectance of two concave cavity mirrorsR3reflectance of the planar cavity mirrorT0s instrumental response timet s timeu(t) negative-step function cm-1the overall absorption coefficient of the gases inside the cavity at the laser wavelength(t) delta function rad
31、 angle of incidence of the test sample m radius of curvature of concave surface of the cavity mirror0, s decay time of the initial and test cavities0, s measurement errors of the decay time of the initial and test cavities5 Test principles5.1 GeneralThe conventional reflectance measurement technique
32、s (spectrophotometry and laser ratiometry) are based on measuring the relative changes of light power reflected by the test sample. The measurement accuracy is limited by the power fluctuations of the light sources. The cavity ring-down (CRD) technique, on the other hand, is based on the measurement
33、 of the decay rate of laser power trapped in a ring-down cavity consisting of at least two highly reflective mirrors. It is therefore totally immune to the power fluctuations of the light sources. The CRD technique can achieve a measurement accuracy that far exceeds the limit set by the power fluctu
34、ations of the light sources.5.2 Decay time of initial cavity and reflectance of cavity mirrorsWhen a laser beam is coupled into the ring-down cavity, it will gradually leak out of the cavity as a small fraction of the light is transmitted through the cavity mirrors at each reflection. The temporal b
35、ehaviour of the cavity output signal immediately after the laser pulse (in the pulsed case, as shown in Figure 1) or immediately after the laser power is switched off in the continuous wave (cw) case, as Table 1 (continued)2 ISO 2015 All rights reservedBS ISO 13142:2015ISO 13142:2015(E)shown in Figu
36、re 2, or at the falling edge of a square-wave modulated power can be expressed as an exponentially decay function of time according to the following decay route given in Formula (1):It It()00exp(1)Where I0is the initial light intensity of the cavity output signal, 0can be expressed as given in Formu
37、la (2):00012=()LcL RRln(2)with Formula (3):c=cn0(3)When at test laser wavelength the absorptance of gases inside the ring-down cavity is negligible, the empty cavity ring-down time, 0, is only dependent upon the cavity length and the reflectance of the cavity mirrors. Formula (2) reduces to Formula
38、(4):0012=LcRRln(4)By experimentally measuring the decay time, 0, the average reflectance of the cavity mirrors can be calculated as Formula (5):RRRLc=1200exp(5)Key1 laser 6 input cavity mirror, concave high reflectance mirror2 mode matching optics 7 output cavity mirror, concave high reflectance mir
39、ror3 initial cavity 8 polarizer4 focusing lens 9 control and data-processing unit5 photo-detector Figure 1 Schematic of optical arrangement for pulsed-CRD technique for high reflectance measurement ISO 2015 All rights reserved 3BS ISO 13142:2015ISO 13142:2015(E)Key1 laser 6 input cavity mirror, conc
40、ave high reflectance mirror2 mode matching optics 7 output cavity mirror, concave high reflectance mirror3 initial cavity 8 polarizer4 focusing lens 9 control and data-processing unit5 photo-detector 10 optical switchFigure 2 Schematic of optical arrangement for cw-CRD technique for high reflectance
41、 measurement5.3 Decay time of test cavity and reflectance of test sampleIf a planar test sample is to be measured, a test ring-down cavity is formed by inserting this test sample into the initial cavity as shown in Figure 3. The incident angle of the laser beam on the test sample follows the require
42、d incident angle of the test sample. In this case, the decay time of the folded test cavity can be expressed as Formula (6): =()LcRRRlns12(6)Therefore, combining Formula (4) and Formula (6), the reflectance Rsof the test sample can be calculated as Formula (7):RLcLcs=exp00(7)Key1 input cavity mirror
43、, concave high reflectance mirror 3 test sample2 output cavity mirror, concave high reflectance mirror4 angle of incidence of test sampleFigure 3 Schematic of optical arrangement for test cavity5.4 High reflectance measurement with an optical feedback CRD techniqueIn the cw-CRD case, an optical feed
44、back CRD (OF-CRD) scheme employing a semiconductor laser as the light source (shown in Figure 4) can be used for the reflectance measurement with an improved signal-to-noise ratio in the CRD signals. In OF-CRD scheme, the initial cavity consists of three cavity mirrors: 4 ISO 2015 All rights reserve
45、dBS ISO 13142:2015ISO 13142:2015(E)two concave mirrors and one planar mirror. The beam from the semiconductor laser is coaxially coupled into the ring-down cavity from the high-reflectance planar cavity mirror. The optical feedback (back-reflection of the laser beam) from the ring-down cavity is ret
46、ro-reflected into the oscillator cavity of the semiconductor laser. Due to the self-mixing effect of the semiconductor laser, the spectral linewidth of the laser is significantly reduced by the frequency selected optical feedback resulting in significant enhancement of the coupling efficiency of the
47、 laser power into the ring-down cavity and therefore, a large increase of the CRD amplitude. When the laser power is modulated by a square wave signal, the cavity decay signal can be obtained at the falling edge of the square wave signal. The test principle is the same as that presented in 5.2 and 5
48、.3. The item RR12in Formula (2) to Formula (6) should be substituted by RR R12 3 in OF-CRD scheme.The following two measurements are necessary to determine the reflectance of the test sample:a) 0and L0are measured with the initial cavity;b) and L are measured with the test cavity.1312121110Key1 semi
49、conductor laser 8 polarizer2 mode matching optics 9 control and data-processing unit3 initial cavity, with three mirrors 10 test sample4 focusing lens 11 angle of incidence of the test sample5 photo-detector 12 input cavity mirror, plane high reflectance mirror6 cavity mirror, concave high reflectance mirror 13 test cavity, with four mirrors7 output cavity mirror, concave high reflectance mirror Figure 4 Schematic of optical arrangement for OF-CRD technique for high reflec
