Optics and photonics - Lasers and laser-related equipment - Test method for absorptance of optical laser components (ISO 11551:2019, Corrected version 2020-01)

This document specifies procedures and techniques for obtaining comparable values for the absorptance of optical laser components.

Optik und Photonik - Laser und Laseranlagen - Prüfverfahren für den Absorptionsgrad von optischen Laserkomponenten (ISO 11551:2019, korrigierte Fassung 2020-01)

Dieses Dokument legt Verfahren und Methoden fest, um vergleichbare Werte für den Absorptionsgrad von optischen Laser-Komponenten zu erhalten.

Optique et photonique - Lasers et équipements associés aux lasers - Méthode d'essai du facteur d'absorption des composants optiques pour lasers (ISO 11551:2019, Version corrigée 2020-01)

Le présent document spécifie les modes opératoires et les techniques utilisés pour obtenir des valeurs comparables du facteur d'absorption des composants optiques pour lasers.

Optika in optični instrumenti - Laserji in laserska oprema - Preskusna metoda za absorpcijo optičnih laserskih komponent (ISO 11551:2019, popravljena verzija 2020-01)

Ta standard določa postopke in tehnike, s katerimi se pridobijo primerljive vrednosti za absorpcijo optičnih laserskih komponent.

General Information

Status
Published
Publication Date
26-Nov-2019
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
27-Nov-2019
Completion Date
27-Nov-2019

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SLOVENSKI STANDARD
SIST EN ISO 11551:2020
01-februar-2020
Nadomešča:
SIST EN ISO 11551:2004
Optika in optični instrumenti - Laserji in laserska oprema - Preskusna metoda za
absorpcijo optičnih laserskih komponent (ISO 11551:2019, popravljena verzija
2020-01)
Optics and photonics - Lasers and laser-related equipment - Test method for

absorptance of optical laser components (ISO 11551:2019, Corrected version 2020-01)

Optik und Photonik - Laser und Laseranlagen - Prüfverfahren für den Absorptionsgrad

von optischen Laserkomponenten (ISO 11551:2019, korrigierte Fassung 2020-01)

Optique et photonique - Lasers et équipements associés aux lasers - Méthode d'essai du

facteur d'absorption des composants optiques pour lasers (ISO 11551:2019, Version

corrigée 2020-01)
Ta slovenski standard je istoveten z: EN ISO 11551:2019
ICS:
31.260 Optoelektronika, laserska Optoelectronics. Laser
oprema equipment
SIST EN ISO 11551:2020 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN ISO 11551:2020
---------------------- Page: 2 ----------------------
SIST EN ISO 11551:2020
EN ISO 11551
EUROPEAN STANDARD
NORME EUROPÉENNE
November 2019
EUROPÄISCHE NORM
ICS 31.260 Supersedes EN ISO 11551:2003
English Version
Optics and photonics - Lasers and laser-related equipment
- Test method for absorptance of optical laser components
(ISO 11551:2019, Corrected version 2020-01)

Optique et photonique - Lasers et équipements Optik und Photonik - Laser und Laseranlagen -

associés aux lasers - Méthode d'essai du facteur Prüfverfahren für den Absorptionsgrad von optischen

d'absorption des composants optiques pour lasers (ISO Laserkomponenten (ISO 11551:2019, korrigierte

11551:2019, Version corrigée 2020-01) Fassung 2020-01)
This European Standard was approved by CEN on 21 October 2019.

This European Standard was corrected and reissued by the CEN-CENELEC Management Centre on 05 February 2020.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this

European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by

translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management

Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATIO N
EUROPÄISCHES KOMITEE FÜR NORMUN G
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 11551:2019 E

worldwide for CEN national Members.
---------------------- Page: 3 ----------------------
SIST EN ISO 11551:2020
EN ISO 11551:2019 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

---------------------- Page: 4 ----------------------
SIST EN ISO 11551:2020
EN ISO 11551:2019 (E)
European foreword

This document (EN ISO 11551:2019) has been prepared by Technical Committee ISO/TC 172 "Optics

and photonics" in collaboration with Technical Committee CEN/TC 123 “Lasers and photonics” the

secretariat of which is held by DIN.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by May 2020, and conflicting national standards shall be

withdrawn at the latest by May 2020.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN ISO 11551:2003.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,

Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of

North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the

United Kingdom.
Endorsement notice

The text of ISO 11551:2019, Corrected version 2020-01 has been approved by CEN as

EN ISO 11551:2019 without any modification.
---------------------- Page: 5 ----------------------
SIST EN ISO 11551:2020
---------------------- Page: 6 ----------------------
SIST EN ISO 11551:2020
INTERNATIONAL ISO
STANDARD 11551
Third edition
2019-10
Corrected version
2020-01
Optics and photonics — Lasers and
laser-related equipment — Test
method for absorptance of optical
laser components
Optique et photonique — Lasers et équipements associés aux lasers
— Méthode d'essai du facteur d'absorption des composants optiques
pour lasers
Reference number
ISO 11551:2019(E)
ISO 2019
---------------------- Page: 7 ----------------------
SIST EN ISO 11551:2020
ISO 11551:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any 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 ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
---------------------- Page: 8 ----------------------
SIST EN ISO 11551:2020
ISO 11551:2019(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Symbols and units of measure ................................................................................................................................................................ 1

5 Preparation of test sample and measuring arrangement ......................................................................................... 2

6 Characteristic features of the laser radiation ........................................................................................................................ 3

7 Test procedure ........................................................................................................................................................................................................ 4

7.1 General ........................................................................................................................................................................................................... 4

7.2 Calibration .................................................................................................................................................................................................. 4

7.2.1 Calibration of the power signal ........................................................................................................................... 4

7.2.2 Calibration of the temperature signal ............................................................................................................ 4

7.2.3 Calibration of the thermal response ............................................................................................................... 4

7.2.4 Measurement of the background signal ...................................................................................................... 5

7.3 Determining the absorptance .................................................................................................................................................... 5

8 Evaluation .................................................................................................................................................................................................................... 5

8.1 General ........................................................................................................................................................................................................... 5

8.2 Elimination of drift .............................................................................................................................................................................. 6

8.3 Exponential method ........................................................................................................................................................................... 6

8.4 Pulse method ............................................................................................................................................................................................ 7

9 Test report ................................................................................................................................................................................................................... 7

Annex A (informative) Effects changing absorptance ......................................................................................................................10

Annex B (informative) Influence of signal distortions ....................................................................................................................12

Annex C (informative) Algorithm for parameterizing the temperature data .........................................................15

Bibliography .............................................................................................................................................................................................................................16

© ISO 2019 – All rights reserved iii
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SIST EN ISO 11551:2020
ISO 11551:2019(E)
Foreword

ISO (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

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 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 document 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 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 not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following

URL: www .iso .org/ iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee 9,

Laser and electro-optical systems.

This third edition cancels and replaces the second edition ISO 11551:2003 which has been technically

revised.
The main changes compared to the previous edition are as follows:

a) Introduction: The assumptions were revised in the second paragraph. Minor wording and example

adjustment in third paragraph.
b) Clause 4: Table for symbols and units was corrected.

c) Clause 5: More detailed specification of environmental conditions for UV- and IR applications are

provided in the second paragraph. ISO 7 specification was deleted.

In the fourth paragraph, Annex A is explicitly mentioned for the dependence of absorption on other

test parameters.

In the fifth paragraph, Annex B is explicitly mentioned to account for the critical issue of finite heat

conductivity.

d) In 7.2.3: In the first paragraph, the calibration procedure is specified in more detail, including the

consideration of the heating scheme for thick samples.
Note 1 is complemented by the restriction for thin samples.

Note 2 is complemented with the consideration of heating scheme for finite heat conduction.

e) In 7.3: In the first paragraph the specifications for the ambient temperature drift were clarified.

The requirements to the total temperature rise during heating were generalized.
iv © ISO 2019 – All rights reserved
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SIST EN ISO 11551:2020
ISO 11551:2019(E)

In the third paragraph the terminology “pre-irradiation” was replaced by “drift record”. The

description of the duration of the cooling period was complemented.

f) In 8.1: In the first paragraph “heat capacity” was replaced by “specific heat capacity”.

g) In A.1: “irradiation dose” added as influencing parameter.
h) In A.3: Generalization of nonlinear absorption dependencies.

i) In B.3: More detailed comments on the convergence of the temperature curves in Figure B.1.

Correction of Formulae (B.2) and (B.3). An additional paragraph with explanations for thick test

samples, including two references.
This corrected version of ISO 11551:2019 incorporates the following corrections:

— In 7.2.3, Formulae (B.1), (B.2) and (B.3), the symbol "α" has been changed into "a";

— Two signs have been corrected in Formula (C.4) to read "−Bexp" and "−t " instead of "Bexp" and "t ".

k k
© ISO 2019 – All rights reserved v
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SIST EN ISO 11551:2020
ISO 11551:2019(E)
Introduction

To characterize an optical component, it is important to know its absorptance. When radiation impinges

upon a component, a part of that radiation is absorbed, increasing the temperature of the component.

In this document only the part of the absorbed power/energy, that is converted into heat, is measured.

If enough energy is absorbed, the optical properties of the component can change, and the component

can even be destroyed. Absorptance is the ratio of the radiant flux absorbed to the radiant flux of the

incident radiation.

In the procedures described in this document, the absorptance is determined calorimetrically as

the ratio of power or energy absorbed by the component to the total power or energy, respectively,

impinging upon the component. The assumption is made that the absorptance of the test sample is

constant within the temperature fluctuations experienced by the component during the measurement.

For most optical bulk materials, the absorptance depends on the position of the irradiating beam on the

sample surface. Several infrared materials exhibit a strong dependence of absorptance on temperature,

especially at high temperatures.
vi © ISO 2019 – All rights reserved
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SIST EN ISO 11551:2020
INTERNATIONAL STANDARD ISO 11551:2019(E)
Optics and photonics — Lasers and laser-related
equipment — Test method for absorptance of optical laser
components
1 Scope

This document specifies procedures and techniques for obtaining comparable values for the

absorptance of optical laser components.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the 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 symbols

ISO 14644-1:2015, Cleanrooms and associated controlled environments — Part 1: Classification of air

cleanliness by particle concentration
ISO 80000-7, Quantities and units — Part 7: Light and radiation
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 11145 and ISO 80000-7 and

the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
absorptance
ratio of the radiant flux absorbed to the radiant flux of the incident radiation

Note 1 to entry: The definition of absorptance used for this document is limited to absorptance processes

which convert the absorbed energy into heat. For certain types of optics and radiation, additional non-thermal

processes can result in absorption losses which will not be detected by the test procedure described here (see

Annex A).
4 Symbols and units of measure
Symbol Term Unit
C Thermal capacity of test sample, holder, etc. J/K
eff
c Specific heat capacity of test sample J/(kg·K)
d , d Beam width on test sample mm
σx σy
m Mass of test sample, holder, etc. kg
P cw power W
© ISO 2019 – All rights reserved 1
---------------------- Page: 13 ----------------------
SIST EN ISO 11551:2020
ISO 11551:2019(E)
Symbol Term Unit
P Average laser power for continuous pulse mode operation W
P Typical peak power for repetitive pulse mode operation W
t Duration of irradiation s
Δt Time interval s
T Ambient temperature K
amb
ΔT Temperature difference K
a Absorptance 1
β Angle of incidence Rad
γ Thermal loss coefficient 1/s
λ Wavelength nm
κ Heat conductivity W/(mK)
η Mass density kg/m
Q Heat source W/m
5 Preparation of test sample and measuring arrangement

Storage, cleaning and the preparation of the test samples are carried out in accordance with the

manufacturer’s instructions for normal use.

The environment of the testing place shall be adapted to the application and test wavelength. It should

consist of dust-free filtered air with less than 50 % relative humidity. The residual dust shall be

reduced in accordance with cleanroom class 7 as defined in ISO 14644-1:2015. However, some specific

spectral ranges might require nitrogen purged environments (deep UV) or zero humidity (several IR

wavelengths). Nitrogen quality for the deep UV range should be at 99,999 % or higher. If these conditions

cannot be supplied, absorption within the surrounding atmosphere will be included in the test result.

An environment free from draughts is very important in order to keep thermal disturbances and heat

loss by convection as small as possible. Measurements in ambient atmosphere and vacuum can have

different influences on the measured absorptance.

A laser shall be used as the radiation source. To keep errors as low as possible, the laser power chosen

for measurements is as high as possible but without causing any deterioration to the component.

Wavelength, angle of incidence and state of polarization of the laser radiation used for the measurement

shall correspond to the values specified by the manufacturer for the use of the test sample. If also ranges

are accepted for these three quantities, any combination of wavelength, angle of incidence and state of

polarization may be chosen from those ranges. The absorption of an optical component can depend on

further parameters, e.g. power density or irradiation dose. In such cases, the measurement sequence

should be chosen individually. For more details, refer to Annex A.

The test sample is mounted in a suitable holder. It is preferable to mount the sample in a manner that

minimizes any thermal contact between the sample and the holder. In this arrangement, the thermal

sensor is attached directly to the sample surface. Reproducible thermal contact between the thermal

sensor and the sample surface is important. Also, care should be taken to maintain constant thermal

impedance between the sample and the holder. Accurate calibration is critically dependent on the

location of the thermal sensor, on the material the sample is made of, and on the sample geometry. Refer

to Annex B for a detailed discussion of these considerations.

It can be difficult to attach the thermal sensor to a small test sample or a sample having an irregular

shape. Such a sample is mounted to the holder in a manner that maximizes thermal contact between

the sample and the holder, while the thermal sensor is attached to or integrated into the holder.

Reproducible thermal contact between the thermal sensor and the holder is important. Also, care

should be taken to maintain constant thermal conductance between the sample and the holder.

2 © ISO 2019 – All rights reserved
---------------------- Page: 14 ----------------------
SIST EN ISO 11551:2020
ISO 11551:2019(E)

In order to increase the precision of the measurements, the sample should be mounted inside a chamber

designed for thermal shielding, with apertures for the laser beam. Special attention shall be given to

ensure that the temperature measurement itself does not cause a change of the sample temperature.

Suitable diaphragms should be placed in the beam path in front of and behind the test sample to ensure

that only the test sample is irradiated by the measuring beam and that reflected or stray radiation

will not strike the holder or the chamber walls. The number of transmissive optics employed for beam

guiding should be minimized in order to reduce possible distortions by multi-reflections or scattered

radiation. The transmitted and reflected partial beams shall be directed on to beam dumps with

minimized back scatter.

Figure 1 shows a schematic measuring arrangement. The curved folding mirror M1 is recommended for

imaging the laser output window on to the sample in order to avoid diffracted radiation influencing the

measurement.
Key
1 laser 7 test sample
2 mirror M1 8 personal computer
3 optical axis 9 beam stop
4 mirror M2 10 thermal sensor
5 test chamber 11 control unit
6 sample holder 12 power detector
Figure 1 — Typical arrangement for measurement of the absorptance
6 Characteristic features of the laser radiation

The following physical quantities are needed for characterizing the laser radiation used for the test:

— wavelength, λ;
— angle of incidence, β;
— state and degree of polarization;
© ISO 2019 – All rights reserved 3
---------------------- Page: 15 ----------------------
SIST EN ISO 11551:2020
ISO 11551:2019(E)
— beam widths on the test sample, d , d ;
σx σy
— average power, P , for cw or continuously pulsed lasers;

— typical peak power, P , and pulse energy Q in the case of continuously pulsed lasers;

— duration of irradiation, t .
7 Test procedure
7.1 General

The following auxiliary tests shall be performed on a regular basis and whenever the measuring

arrangement has been altered.
7.2 Calibration
7.2.1 Calibration of the power signal

Calibrate the power signal by placing a calibrated laser power detector at the location of the test

components and, in order to obtain correct calibration, compare the measured laser power to the signal

of the power monitor used during absorptance tests.
7.2.2 Calibration of the temperature signal

Calibrate the temperature signal by fixing a test sample, to which a calibrated thermal sensor is

attached, to the sample holder. Compare the temperature signals of this calibrated sensor and the

sensors used during absorptance tests while varying the ambient temperature slowly over the linearity

range of the temperature detectors at the typical test temperature.
7.2.3 Calibration of the thermal response

For certain types of sample materials and geometries, the temperature rise induced by the absorbed

heat may differ from the theoretical response expected for ideal materials having infinite thermal

conductivity. In these cases, a correction factor f shall be determined, which compensates for the

influence of such phenomena on the absorptance test result. f is unity if the influence of limited

thermal conductivity can be neglected. In order to derive a correct value for f , the heating scheme

of the calibration routine needs to be consistent with the heating characteristic of the samples to be

tested. Surface absorbers shall be related to a correction factor derived from a calibration based on

surface heating. And a bulk absorber shall be corrected with a bulk heated calibration sample.

For calibration, a reference sample of known absorptance, which is identical to the samples under

investigation with respect to substrate geometry and thermal diffusivity, is tested for absorptance as

described below. The irradiation time and evaluation method used for calibration shall be the same as

for the sample under test.

Depending on the evaluation method used for the absorptance test, the correction coefficient can be

calculated by substituting the value of the known calibration sample absorptance for a in Formula (2)

(see 8.3) or Formula (5) (see 8.4), and solving for f .

A known absorptance can be achieved by applying a thin, high-absorbing coating to the sample surface

area that is exposed to irradiation. High absorptance values can be determined with sufficient accuracy,

e.g. by measuring the fraction of transmitted, reflected and scattered radiation. For absorptance testing

of samples with high absorptance values, the laser power should be suitably attenuated in order to

avoid damage to the samples and to ensure that the resulting temperature rise is in the same order

of magnitude as the temperature which is achieved for typical measurements. This procedure applies

only for samples of high surface absorption, where bulk absorption can be neglected.

4 © ISO 2019 – All rights reserved
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SIST EN ISO 11551:2020
ISO 11551:2019(E)

As an alternative to irradiating a calibration sample of known absorptance with the laser beam, the

thermal energy may be deposited electrically in the test sample by attaching an electric resistor to

the tested surface. The absorbed power is given by RI , where R is the electrical resistance and I is the

electric current during “irradiation”. Care should be taken to ensure good thermal contact between

resistor and sample. Furthermore, especially in the case of samples with low thermal conductivity, the

area of the resistor should match the area irradiated by the laser beam under normal test conditions.

This procedure can in principle be applied to both surface and bulk absorbing samples. Care should be

taken to ensure that the heating scheme of the calibration sample is close or identical to the expected

heating scheme of the test samples.
7.2.4 Measurement of the background signal

For maximum accuracy and suppression of possible signal distortions, the imaging and alignment of

the laser beam shall be optimized. A measurement with an empty holder or with an absorptance-free

component can be used to verify that the measuring arrangement is not influenced by reflected or stray

radiation. The amplitude of the temperature fluctuations during the test interval shall be at least one

order of magnitude below the temperature rise occurring during an absorptance test.

7.3 Determining the absorptance
The absorptance of optical components is d
...

SLOVENSKI STANDARD
SIST EN ISO 11551:2020
01-februar-2020
Nadomešča:
SIST EN ISO 11551:2004
Optika in optični instrumenti - Laserji in laserska oprema - Preskusna metoda za
absorpcijo optičnih laserskih komponent (ISO 11551:2019)
Optics and photonics - Lasers and laser-related equipment - Test method for
absorptance of optical laser components (ISO 11551:2019)

Optik und Photonik - Laser und Laseranlagen - Prüfverfahren für den Absorptionsgrad

von optischen Laserkomponenten (ISO 11551:2019)

Optique et photonique - Lasers et équipements associés aux lasers - Méthode d'essai du

facteur d'absorption des composants optiques pour lasers (ISO 11551:2019)
Ta slovenski standard je istoveten z: EN ISO 11551:2019
ICS:
31.260 Optoelektronika, laserska Optoelectronics. Laser
oprema equipment
SIST EN ISO 11551:2020 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN ISO 11551:2020
---------------------- Page: 2 ----------------------
SIST EN ISO 11551:2020
EN ISO 11551
EUROPEAN STANDARD
NORME EUROPÉENNE
November 2019
EUROPÄISCHE NORM
ICS 31.260 Supersedes EN ISO 11551:2003
English Version
Optics and photonics - Lasers and laser-related equipment
- Test method for absorptance of optical laser components
(ISO 11551:2019)

Optique et photonique - Lasers et équipements Optik und Photonik - Laser und Laseranlagen -

associés aux lasers - Méthode d'essai du facteur Prüfverfahren für den Absorptionsgrad von optischen

d'absorption des composants optiques pour lasers (ISO Laserkomponenten (ISO 11551:2019)

11551:2019)
This European Standard was approved by CEN on 21 October 2019.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this

European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by

translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management

Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 11551:2019 E

worldwide for CEN national Members.
---------------------- Page: 3 ----------------------
SIST EN ISO 11551:2020
EN ISO 11551:2019 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

---------------------- Page: 4 ----------------------
SIST EN ISO 11551:2020
EN ISO 11551:2019 (E)
European foreword

This document (EN ISO 11551:2019) has been prepared by Technical Committee ISO/TC 172 "Optics

and photonics" in collaboration with Technical Committee CEN/TC 123 “Lasers and photonics” the

secretariat of which is held by DIN.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by May 2020, and conflicting national standards shall be

withdrawn at the latest by May 2020.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN ISO 11551:2003.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,

Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of

North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the

United Kingdom.
Endorsement notice

The text of ISO 11551:2019 has been approved by CEN as EN ISO 11551:2019 without any modification.

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SIST EN ISO 11551:2020
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SIST EN ISO 11551:2020
INTERNATIONAL ISO
STANDARD 11551
Third edition
2019-10
Optics and photonics — Lasers and
laser-related equipment — Test
method for absorptance of optical
laser components
Optique et photonique — Lasers et équipements associés aux lasers
— Méthode d'essai du facteur d'absorption des composants optiques
pour lasers
Reference number
ISO 11551:2019(E)
ISO 2019
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SIST EN ISO 11551:2020
ISO 11551:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

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Email: copyright@iso.org
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Published in Switzerland
ii © ISO 2019 – All rights reserved
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SIST EN ISO 11551:2020
ISO 11551:2019(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Symbols and units of measure ................................................................................................................................................................ 1

5 Preparation of test sample and measuring arrangement ......................................................................................... 2

6 Characteristic features of the laser radiation ........................................................................................................................ 3

7 Test procedure ........................................................................................................................................................................................................ 4

7.1 General ........................................................................................................................................................................................................... 4

7.2 Calibration .................................................................................................................................................................................................. 4

7.2.1 Calibration of the power signal ........................................................................................................................... 4

7.2.2 Calibration of the temperature signal ............................................................................................................ 4

7.2.3 Calibration of the thermal response ............................................................................................................... 4

7.2.4 Measurement of the background signal ...................................................................................................... 5

7.3 Determining the absorptance .................................................................................................................................................... 5

8 Evaluation .................................................................................................................................................................................................................... 5

8.1 General ........................................................................................................................................................................................................... 5

8.2 Elimination of drift .............................................................................................................................................................................. 6

8.3 Exponential method ........................................................................................................................................................................... 6

8.4 Pulse method ............................................................................................................................................................................................ 7

9 Test report ................................................................................................................................................................................................................... 7

Annex A (informative) Effects changing absorptance ......................................................................................................................10

Annex B (informative) Influence of signal distortions ....................................................................................................................12

Annex C (informative) Algorithm for parameterizing the temperature data .........................................................15

Bibliography .............................................................................................................................................................................................................................16

© ISO 2019 – All rights reserved iii
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SIST EN ISO 11551:2020
ISO 11551:2019(E)
Foreword

ISO (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

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 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 document 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 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 not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following

URL: www .iso .org/ iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee 9,

Laser and electro-optical systems.

This third edition cancels and replaces the second edition ISO 11551:2003 which has been technically

revised.
The main changes compared to the previous edition are as follows:

a) Introduction: The assumptions were revised in the second paragraph. Minor wording and example

adjustment in third paragraph.
b) Clause 4: Table for symbols and units was corrected.

c) Clause 5: More detailed specification of environmental conditions for UV- and IR applications are

provided in the second paragraph. ISO 7 specification was deleted.

In the fourth paragraph, Annex A is explicitly mentioned for the dependence of absorption on other

test parameters.

In the fifth paragraph, Annex B is explicitly mentioned to account for the critical issue of finite heat

conductivity.

d) In 7.2.3: In the first paragraph, the calibration procedure is specified in more detail, including the

consideration of the heating scheme for thick samples.
Note 1 is complemented by the restriction for thin samples.

Note 2 is complemented with the consideration of heating scheme for finite heat conduction.

e) In 7.3: In the first paragraph the specifications for the ambient temperature drift were clarified.

The requirements to the total temperature rise during heating were generalized.
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In the third paragraph the terminology “pre-irradiation” was replaced by “drift record”. The

description of the duration of the cooling period was complemented.

f) In 8.1: In the first paragraph “heat capacity” was replaced by “specific heat capacity”.

g) In A.1: “irradiation dose” added as influencing parameter.
h) In A.3: Generalization of nonlinear absorption dependencies.

i) In B.3: More detailed comments on the convergence of the temperature curves in Figure B.1.

Correction of Formulae (B.2) and (B.3). An additional paragraph with explanations for thick test

samples, including two references.
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Introduction

To characterize an optical component, it is important to know its absorptance. When radiation impinges

upon a component, a part of that radiation is absorbed, increasing the temperature of the component.

In this document only the part of the absorbed power/energy, that is converted into heat, is measured.

If enough energy is absorbed, the optical properties of the component can change, and the component

can even be destroyed. Absorptance is the ratio of the radiant flux absorbed to the radiant flux of the

incident radiation.

In the procedures described in this document, the absorptance is determined calorimetrically as

the ratio of power or energy absorbed by the component to the total power or energy, respectively,

impinging upon the component. The assumption is made that the absorptance of the test sample is

constant within the temperature fluctuations experienced by the component during the measurement.

For most optical bulk materials, the absorptance depends on the position of the irradiating beam on the

sample surface. Several infrared materials exhibit a strong dependence of absorptance on temperature,

especially at high temperatures.
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SIST EN ISO 11551:2020
INTERNATIONAL STANDARD ISO 11551:2019(E)
Optics and photonics — Lasers and laser-related
equipment — Test method for absorptance of optical laser
components
1 Scope

This document specifies procedures and techniques for obtaining comparable values for the

absorptance of optical laser components.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the 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 symbols

ISO 14644-1:2015, Cleanrooms and associated controlled environments — Part 1: Classification of air

cleanliness by particle concentration
ISO 80000-7, Quantities and units — Part 7: Light and radiation
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 11145 and ISO 80000-7 and

the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
absorptance
ratio of the radiant flux absorbed to the radiant flux of the incident radiation

Note 1 to entry: The definition of absorptance used for this document is limited to absorptance processes

which convert the absorbed energy into heat. For certain types of optics and radiation, additional non-thermal

processes can result in absorption losses which will not be detected by the test procedure described here (see

Annex A).
4 Symbols and units of measure
Symbol Term Unit
C Thermal capacity of test sample, holder, etc. J/K
eff
c Specific heat capacity of test sample J/(kg·K)
d , d Beam width on test sample mm
σx σy
m Mass of test sample, holder, etc. kg
P cw power W
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Symbol Term Unit
P Average laser power for continuous pulse mode operation W
P Typical peak power for repetitive pulse mode operation W
t Duration of irradiation s
Δt Time interval s
T Ambient temperature K
amb
ΔT Temperature difference K
a Absorptance 1
β Angle of incidence Rad
γ Thermal loss coefficient 1/s
λ Wavelength nm
κ Heat conductivity W/(mK)
η Mass density kg/m
Q Heat source W/m
5 Preparation of test sample and measuring arrangement

Storage, cleaning and the preparation of the test samples are carried out in accordance with the

manufacturer’s instructions for normal use.

The environment of the testing place shall be adapted to the application and test wavelength. It should

consist of dust-free filtered air with less than 50 % relative humidity. The residual dust shall be

reduced in accordance with cleanroom class 7 as defined in ISO 14644-1:2015. However, some specific

spectral ranges might require nitrogen purged environments (deep UV) or zero humidity (several IR

wavelengths). Nitrogen quality for the deep UV range should be at 99,999 % or higher. If these conditions

cannot be supplied, absorption within the surrounding atmosphere will be included in the test result.

An environment free from draughts is very important in order to keep thermal disturbances and heat

loss by convection as small as possible. Measurements in ambient atmosphere and vacuum can have

different influences on the measured absorptance.

A laser shall be used as the radiation source. To keep errors as low as possible, the laser power chosen

for measurements is as high as possible but without causing any deterioration to the component.

Wavelength, angle of incidence and state of polarization of the laser radiation used for the measurement

shall correspond to the values specified by the manufacturer for the use of the test sample. If also ranges

are accepted for these three quantities, any combination of wavelength, angle of incidence and state of

polarization may be chosen from those ranges. The absorption of an optical component can depend on

further parameters, e.g. power density or irradiation dose. In such cases, the measurement sequence

should be chosen individually. For more details, refer to Annex A.

The test sample is mounted in a suitable holder. It is preferable to mount the sample in a manner that

minimizes any thermal contact between the sample and the holder. In this arrangement, the thermal

sensor is attached directly to the sample surface. Reproducible thermal contact between the thermal

sensor and the sample surface is important. Also, care should be taken to maintain constant thermal

impedance between the sample and the holder. Accurate calibration is critically dependent on the

location of the thermal sensor, on the material the sample is made of, and on the sample geometry. Refer

to Annex B for a detailed discussion of these considerations.

It can be difficult to attach the thermal sensor to a small test sample or a sample having an irregular

shape. Such a sample is mounted to the holder in a manner that maximizes thermal contact between

the sample and the holder, while the thermal sensor is attached to or integrated into the holder.

Reproducible thermal contact between the thermal sensor and the holder is important. Also, care

should be taken to maintain constant thermal conductance between the sample and the holder.

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In order to increase the precision of the measurements, the sample should be mounted inside a chamber

designed for thermal shielding, with apertures for the laser beam. Special attention shall be given to

ensure that the temperature measurement itself does not cause a change of the sample temperature.

Suitable diaphragms should be placed in the beam path in front of and behind the test sample to ensure

that only the test sample is irradiated by the measuring beam and that reflected or stray radiation

will not strike the holder or the chamber walls. The number of transmissive optics employed for beam

guiding should be minimized in order to reduce possible distortions by multi-reflections or scattered

radiation. The transmitted and reflected partial beams shall be directed on to beam dumps with

minimized back scatter.

Figure 1 shows a schematic measuring arrangement. The curved folding mirror M1 is recommended for

imaging the laser output window on to the sample in order to avoid diffracted radiation influencing the

measurement.
Key
1 laser 7 test sample
2 mirror M1 8 personal computer
3 optical axis 9 beam stop
4 mirror M2 10 thermal sensor
5 test chamber 11 control unit
6 sample holder 12 power detector
Figure 1 — Typical arrangement for measurement of the absorptance
6 Characteristic features of the laser radiation

The following physical quantities are needed for characterizing the laser radiation used for the test:

— wavelength, λ;
— angle of incidence, β;
— state and degree of polarization;
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SIST EN ISO 11551:2020
ISO 11551:2019(E)
— beam widths on the test sample, d , d ;
σx σy
— average power, P , for cw or continuously pulsed lasers;

— typical peak power, P , and pulse energy Q in the case of continuously pulsed lasers;

— duration of irradiation, t .
7 Test procedure
7.1 General

The following auxiliary tests shall be performed on a regular basis and whenever the measuring

arrangement has been altered.
7.2 Calibration
7.2.1 Calibration of the power signal

Calibrate the power signal by placing a calibrated laser power detector at the location of the test

components and, in order to obtain correct calibration, compare the measured laser power to the signal

of the power monitor used during absorptance tests.
7.2.2 Calibration of the temperature signal

Calibrate the temperature signal by fixing a test sample, to which a calibrated thermal sensor is

attached, to the sample holder. Compare the temperature signals of this calibrated sensor and the

sensors used during absorptance tests while varying the ambient temperature slowly over the linearity

range of the temperature detectors at the typical test temperature.
7.2.3 Calibration of the thermal response

For certain types of sample materials and geometries, the temperature rise induced by the absorbed

heat may differ from the theoretical response expected for ideal materials having infinite thermal

conductivity. In these cases, a correction factor f shall be determined, which compensates for the

influence of such phenomena on the absorptance test result. f is unity if the influence of limited

thermal conductivity can be neglected. In order to derive a correct value for f , the heating scheme

of the calibration routine needs to be consistent with the heating characteristic of the samples to be

tested. Surface absorbers shall be related to a correction factor derived from a calibration based on

surface heating. And a bulk absorber shall be corrected with a bulk heated calibration sample.

For calibration, a reference sample of known absorptance, which is identical to the samples under

investigation with respect to substrate geometry and thermal diffusivity, is tested for absorptance as

described below. The irradiation time and evaluation method used for calibration shall be the same as

for the sample under test.

Depending on the evaluation method used for the absorptance test, the correction coefficient can be

calculated by substituting the value of the known calibration sample absorptance for α in Formula (2)

(see 8.3) or Formula (5) (see 8.4), and solving for f .

A known absorptance can be achieved by applying a thin, high-absorbing coating to the sample surface

area that is exposed to irradiation. High absorptance values can be determined with sufficient accuracy,

e.g. by measuring the fraction of transmitted, reflected and scattered radiation. For absorptance testing

of samples with high absorptance values, the laser power should be suitably attenuated in order to

avoid damage to the samples and to ensure that the resulting temperature rise is in the same order

of magnitude as the temperature which is achieved for typical measurements. This procedure applies

only for samples of high surface absorption, where bulk absorption can be neglected.

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As an alternative to irradiating a calibration sample of known absorptance with the laser beam, the

thermal energy may be deposited electrically in the test sample by attaching an electric resistor to

the tested surface. The absorbed power is given by RI , where R is the electrical resistance and I is the

electric current during “irradiation”. Care should be taken to ensure good thermal contact between

resistor and sample. Furthermore, especially in the case of samples with low thermal conductivity, the

area of the resistor should match the area irradiated by the laser beam under normal test conditions.

This procedure can in principle be applied to both surface and bulk absorbing samples. Care should be

taken to ensure that the heating scheme of the calibration sample is close or identical to the expected

heating scheme of the test samples.
7.2.4 Measurement of the background signal

For maximum accuracy and suppression of possible signal distortions, the imaging and alignment of

the laser beam shall be optimized. A measurement with an empty holder or with an absorptance-free

component can be used to verify that the measuring arrangement is not influenced by reflected or stray

radiation. The amplitude of the temperature fluctuations during the test interval shall be at least one

order of magnitude below the temperature rise occurring during an absorptance test.

7.3 Determining the absorptance

The absorptance of optical components is determined calorimetrically by means of a measuring

arrangement as shown in Figure 1. Before measurement commences, thermal equilibrium shall be

established, so that the ambient temperature drift is approximately linear and the temperature noise

(standard deviation) is at least one order of magnitude below the maximum temperature rise induced

by irradiation. The maximum temperature rise during the test should be in accordance to the linearity

of the temperature detector.

If the absorptance is dependent either on the power or energy density of the impinging radiation, or the

irradiation dose, this shall be noted in the test report. The te
...

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