prEN ISO 11551

SLOVENSKI STANDARD
01-julij-2025
Optika in optični instrumenti - Laserji in laserska oprema - Preskusna metoda za
absorpcijo optičnih laserskih komponent (ISO/DIS 11551:2025)
Optics and photonics - Lasers and laser-related equipment - Test method for
absorptance of optical laser components (ISO/DIS 11551:2025)
Optik und Photonik - Laser und Laseranlagen - Prüfverfahren für den Absorptionsgrad
von optischen Laserkomponenten (ISO/DIS 11551:2025)
Optique et photonique - Lasers et équipements associés aux lasers - Méthode d'essai du
facteur d'absorption des composants optiques pour lasers (ISO/DIS 11551:2025)
Ta slovenski standard je istoveten z: prEN ISO 11551
ICS:
31.260 Optoelektronika, laserska Optoelectronics. Laser
oprema equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 11551
ISO/TC 172/SC 9
Optics and photonics — Lasers and
Secretariat: DIN
laser-related equipment — Test
Voting begins on:
method for absorptance of optical
2025-05-22
laser components
Voting terminates on:
2025-08-14
Optique et photonique — Lasers et équipements associés aux
lasers — Méthode d'essai du facteur d'absorption des composants
optiques pour lasers
ICS: 31.260
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
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RECIPIENTS OF THIS DRAFT ARE INVITED
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NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 11551:2025(en)
DRAFT
ISO/DIS 11551:2025(en)
International
Standard
ISO/DIS 11551
ISO/TC 172/SC 9
Optics and photonics — Lasers and
Secretariat: DIN
laser-related equipment — Test
Voting begins on:
method for absorptance of optical
laser components
Voting terminates on:
Optique et photonique — Lasers et équipements associés aux
lasers — Méthode d'essai du facteur d'absorption des composants
optiques pour lasers
ICS: 31.260
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
BE CONSIDERED IN THE LIGHT OF THEIR
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
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WHICH REFERENCE MAY BE MADE IN
or ISO’s member body in the country of the requester.
NATIONAL REGULATIONS.
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TO SUBMIT, WITH THEIR COMMENTS,
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NOTIFICATION OF ANY RELEVANT PATENT
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Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 11551:2025(en)
ii
ISO/DIS 11551:2025(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 . 4
7.1 General .4
7.2 Calibration .4
7.2.1 Calibration of the radiant 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 . 6
8.1 General .6
8.2 Elimination of drift .6
8.3 Exponential method .6
8.4 Pulse method .7
9 Test report . 8
Annex A (informative) Effects changing absorptance . 10
Annex B (informative) Influence of signal distortions .13
Annex C (informative) Algorithm for parameterizing the temperature data .16
Bibliography . 17

iii
ISO/DIS 11551:2025(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 09, Laser
and electro-optical systems.
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 equations and figures;
— modified text and additional figures in sections A1 and A3 of Annex A
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/DIS 11551:2025(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
DRAFT International Standard ISO/DIS 11551:2025(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 14644-1:2015, 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 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/DIS 11551:2025(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/(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 relative humidity between 40 % and 60 %. 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. At high power
densities, 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.
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

ISO/DIS 11551:2025(en)
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.
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 radiant power detector
Figure 1 — Typical arrangement for measurement of the absorptance

ISO/DIS 11551:2025(en)
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
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 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, whi
...