SIST EN ISO 11551:2020

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
• Public Enquiry End Date: 24-Jan-2019
• Publication Date: 12-Jan-2020
• ICS: 31.260 - Optoelectronics. Laser equipment
• Technical Committee: VAZ - Healthcare
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 11-Dec-2019
• Due Date: 15-Feb-2020
• Completion Date: 13-Jan-2020
• Ref Project: EN ISO 11551:2019 - Optics and photonics - Lasers and laser-related equipment - Test method for absorptance of optical laser components (ISO 11551:2019, Corrected version 2020-01)

Relations

• Replaces: SIST EN ISO 11551:2004 - Optics and optical instruments - Lasers and laser-related equipment - Test method for absorptance of optical laser components (ISO 11551:2003)
• Effective Date: 01-Feb-2020
• Revised: oSIST prEN ISO 11551:2025 - Optics and photonics - Lasers and laser-related equipment - Test method for absorptance of optical laser components (ISO/DIS 11551:2025)
• Effective Date: 25-Sep-2024

Overview

EN ISO 11551:2019 (Corrected version 2020-01) - adopted by CEN - defines a calibrated, reproducible test method for absorptance of optical laser components. The standard specifies procedures to obtain comparable values of absorptance by calorimetric measurement: absorptance is reported as the ratio of radiant flux converted into heat and absorbed by the component to the incident radiant flux. The method assumes absorptance remains effectively constant during the temperature changes experienced in the test and notes that only thermally converted absorption is measured (non‑thermal processes are not detected).

Key topics and technical requirements

• Scope and definition of absorptance specific to laser‑related optics.
• Test sample preparation and measuring arrangement - environmental and sample handling considerations for reliable results.
• Characterization of laser radiation used for the test (beam parameters and stability).
• Calibration procedures:
  • Calibration of power and temperature signals.
  • Calibration of the thermal response of the sample/holder.
  • Measurement and subtraction of background signals.
• Test procedures for continuous and pulsed operation, including requirements for drift control and heating limits.
• Data evaluation methods:
  • Drift elimination techniques.
  • The exponential method and pulse method for extracting absorptance from temperature-time data.
• Reporting requirements specifying necessary information in the test report.
• Informative annexes covering effects that change absorptance, signal distortions and a parameterization algorithm for temperature data.

Practical applications

• Quantifying heat load from laser irradiation on optical components (lenses, mirrors, windows, coatings).
• Supporting component specification, acceptance testing and quality control where laser-induced heating is a concern.
• Informing design decisions for thermal management and assessing suitability of materials/components for high-power laser systems.
• Providing comparable absorptance data for suppliers, test laboratories and research groups working in optics and photonics.

Who uses this standard

• Optical component manufacturers and coating vendors
• Laser system designers and integrators
• Test laboratories and calibration facilities
• R&D groups in photonics and materials science
• Procurement and quality assurance teams requiring standardized absorptance data

Related standards (normative references)

• ISO 11145 (vocabulary and symbols for lasers)
• ISO 14644‑1 (cleanroom classification)
• ISO 80000‑7 (quantities and units - light and radiation)

Keywords: EN ISO 11551, ISO 11551:2019, absorptance measurement, optical laser components, calorimetric test method, lasers, photonics, absorptance standard.

Standards Content (Sample)

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

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.

Contents Page
European foreword . 3

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.

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
ISO 11551:2019(E)
© 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: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

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 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

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.
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

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
a
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)
p
d , d Beam width on test sample mm
σx σy
m Mass of test sample, holder, etc. kg
i
P cw power W
ISO 11551:2019(E)
Symbol Term Unit
P Average laser power for continuous pulse mode operation W
av
P Typical peak power for repetitive pulse mode operation W
pk
t Duration of irradiation s
B
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

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 opti
...

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

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.

Contents Page
European foreword . 3

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
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
ISO 11551:2019(E)
© 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: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

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 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

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 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

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
a
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)
p
d , d Beam width on test sample mm
σx σy
m Mass of test sample, holder, etc. kg
i
P cw power W
ISO 11551:2019(E)
Symbol Term Unit
P Average laser power for continuous pulse mode operation W
av
P Typical peak power for repetitive pulse mode operation W
pk
t Duration of irradiation s
B
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

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 cau
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