SIST EN ISO 11551:2026

• Abstract:

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

• Status: Published
• Public Enquiry End Date: 30-Jul-2025
• Publication Date: 16-Sep-2026
• ICS: 31.260 - Optoelectronics. Laser equipment
• Technical Committee: VAZ - Healthcare
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 04-Sep-2026
• Due Date: 09-Nov-2026
• Completion Date: 17-Sep-2026
• Ref Project: EN ISO 11551:2026 - Optics and photonics - Lasers and laser-related equipment - Test method for absorptance of optical laser components (ISO 11551:2026)

• Replaces: 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)
• Effective Date: 01-Oct-2026

Overview

SIST EN ISO 11551:2026 sets out standardized procedures for measuring the absorptance of optical laser components. Absorptance is a critical property in the field of optics and photonics, impacting the performance, durability, and safety of lasers and laser-related equipment. This international standard, developed by SIST and aligned with ISO 11551, ensures the reliability and comparability of absorptance measurements across different laboratories and industries.

The document provides comprehensive guidance on the preparation of test samples, calibration of measurement equipment, test environment setup, and methods for calculating absorptance. By following this standard, manufacturers and users of optical components can confidently evaluate how much radiant laser energy is absorbed as heat, an essential factor in component selection and laser system design.

Key Topics

• Scope and Purpose: Defines procedures for achieving consistent values for the absorptance of optical laser components.
• Terms and Definitions: Clarifies key terminology such as absorptance, radiant flux, and related measurement units.
• Preparation and Calibration:
  • Guidelines for sample handling, cleaning, and environmental conditions (e.g., cleanroom requirements, humidity, and temperature control).
  • Calibration steps for radiation sources, thermal and power sensors.
• Test Arrangements:
  • Recommendations for mounting samples and positioning sensors to reduce measurement errors.
  • Schematic layouts for experimental setups ensuring accurate irradiance and temperature data.
• Measurement Procedures:
  • Step-by-step process for conducting absorptance tests, including drift, heating, and cooling intervals.
  • Use of exponential and pulse methods for evaluation.
• Reporting Requirements:
  • Essential elements for a comprehensive test report, such as sample details, equipment parameters, test results, and environmental factors.

Applications

ISO 11551:2026 is widely applicable in industries and research fields relying on precision laser and optical technologies, including:

• Laser Manufacturing and Integration: Helps verify the thermal stability and optical loss of lenses, coatings, mirrors, and other components used in high-power laser systems.
• Quality Assurance: Ensures repeatable and reliable measurements for product certification, procurement, and compliance with international regulations.
• R&D and Innovation: Enables researchers to study effects such as nonlinear absorption, ageing, contamination, and cleaning methods on absorptance, driving material and process improvements.
• Safety Assessment: Provides data to avoid overheating or laser-induced damage in optical systems, supporting the safe operation of laser equipment in medical, industrial, and scientific applications.
• Maintenance and Lifecycle Management: Allows ongoing monitoring of component degradation, supporting preventative maintenance strategies for laser systems.

Related Standards

For effective implementation and broader context, the following related international standards should be considered:

• ISO 11145: Optics and photonics - Lasers and laser-related equipment - Vocabulary and symbols.
• ISO 14644-1:2015: Cleanrooms and associated controlled environments - Classification of air cleanliness by particle concentration.
• ISO 80000-7: Quantities and units - Part 7: Light and radiation.

Utilizing these standards alongside ISO 11551:2026 enhances measurement consistency, laboratory safety, and integration with global optoelectronics and laser equipment quality systems.

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Keywords: ISO 11551:2026, absorptance, optical laser components, optics and photonics, laser testing, measurement procedures, laser equipment standard, calibration, test report, cleanroom, SIST, international standard.

SLOVENSKI STANDARD
01-oktober-2026
Nadomešča:
SIST EN ISO 11551:2020
Optika in optični instrumenti - Laserji in laserska oprema - Preskusna metoda za
absorpcijo optičnih laserskih komponent (ISO 11551:2026)
Optics and photonics - Lasers and laser-related equipment - Test method for
absorptance of optical laser components (ISO 11551:2026)
Optik und Photonik - Laser und Laseranlagen - Prüfverfahren für den Absorptionsgrad
von optischen Laserkomponenten (ISO 11551:2026)
Optique et photonique - Lasers et équipements associés aux lasers - Méthode d'essai du
facteur d'absorption des composants optiques pour lasers (ISO 11551:2026)
Ta slovenski standard je istoveten z: EN ISO 11551:2026
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
August 2026
EUROPÄISCHE NORM
ICS 31.260 Supersedes EN ISO 11551:2019
English Version
Optics and photonics - Lasers and laser-related equipment
- Test method for absorptance of optical laser components
(ISO 11551:2026)
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 11551:2026)
11551:2026)
This European Standard was approved by CEN on 22 August 2026.

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, Türkiye 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
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 11551:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 11551:2026) 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 February 2027, and conflicting national standards
shall be withdrawn at the latest by February 2027.
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 11551:2019.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
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, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 11551:2026 has been approved by CEN as EN ISO 11551:2026 without any modification.

International
Standard
ISO 11551
Fourth edition
Optics and photonics — Lasers and
2026-08
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 11551:2026(en) © ISO 2026
ISO 11551:2026(en)
© ISO 2026
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]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
ISO 11551:2026(en)
Contents Page
Foreword .iv
Introduction .v
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 . 4
7 Test procedure . 5
7.1 General .5
7.2 Calibration .5
7.2.1 Calibration of the radiant power signal .5
7.2.2 Calibration of the temperature signal .5
7.2.3 Calibration of the thermal response .5
7.2.4 Measurement of the background signal .6
7.3 Determining the absorptance .6
8 Evaluation . 6
8.1 General .6
8.2 Elimination of drift .7
8.3 Exponential method .7
8.4 Pulse method .8
9 Test report . 9
Annex A (informative) Effects changing absorptance .11
Annex B (informative) Influence of signal distortions . 14
Annex C (informative) Algorithm for parameterizing the temperature data . 17
Bibliography .18

iii
ISO 11551:2026(en)
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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee 172, Optics and photonics, Subcommittee SC 9, Laser
and electro-optical systems, in collaboration with the European Committee for Standardization (CEN)
Technical Committee CEN/TC 123, Lasers and photonics, in accordance with the Agreement on technical
cooperation between ISO and CEN (Vienna Agreement).
This fourth edition cancels and replaces the third edition (ISO 11551:2019), which has been technically
revised.
The main changes are as follows:
— harmonization of terms and environmental conditions to current laser measurement standards;
— minor adjustments of formulae and figures;
— modified text and additional figures in A.1 and A.3.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
ISO 11551:2026(en)
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 radiant power/energy, that is converted into heat, is measured. If
enough radiant 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 radiant power or radiant energy absorbed by the component to the total radiant power or radiant 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.

v
International Standard ISO 11551:2026(en)
Optics and photonics — Lasers and laser-related equipment
— Test method for absorptance of optical laser components
WARNING — Laser calorimetric measurements may involve high power lasers, the use of which
may come with significant risks, which may include, but are not limited to; eye injury to people;
laser burns to people or equipment; ignition of materials; generating debris of toxic materials in
the substrate or coating; electrical hazards. It is the responsibility of the user to comply with local
guidelines and regulations for their particular set-up.
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, 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 terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// 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 radiant energy to 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
The symbols and units of measurement used are the following:

ISO 11551:2026(en)
Table 1 — Symbols and units of measure
Symbol Term Unit
Thermal capacity of test sample, holder, etc. J/K
Ceff
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 radiant power W
P Average laser power for continuous pulse mode operation W
av
Typical peak radiant power for repetitive pulse mode oper-
P W
pk
ation
t Duration of irradiation s
B
t Duration of cooling s
C
t Duration of drift s
D
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/(m·K)
η Mass density kg/m
σ Error sum —
min
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 relative humidity between 40 % and 60 %. The residual dust shall be
reduced in accordance with cleanroom class 7 as defined in ISO 14644-1. However, some specific spectral
ranges could 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. At high
irradiance, it shall be ensured that the sample is not damaged. This shall be ensured by the fact that the
measurement shall be reproducible within the specified error limits.
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. irradiance or irradiation dose. In such cases, the measurement sequence should be
chosen individually. For more details, refer to Annex A.

ISO 11551:2026(en)
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.
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.
ISO 11551:2026(en)
Key
1 laser
2 mirror M1
3 optical axis
4 mirror M2
5 test chamber
6 sample holder
7 test sample
8 personal computer
9 beam stop
10 thermal sensor
11 control unit
12 radiant 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;
— beam widths on the test sample, d , d ;
σx σy
— average radiant power, P , for cw or continuously pulsed lasers;
av
— typical peak radiant power, P , and pulse energy, Q, in the case of pulsed lasers;
pk
— duration of irradiation, t .
B
ISO 11551:2026(en)
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 radiant power signal
Calibrate the radiant 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 use
...