SIST EN ISO 21254-1:2025

SLOVENSKI STANDARD
01-november-2025
Nadomešča:
SIST EN ISO 21254-1:2011
Laserji in z laserji povezana oprema - Preskusne metode za ugotavljanje praga
poškodbe, povzročene z laserjem - 1. del: Definicije in splošna načela (ISO 21254-
1:2025)
Lasers and laser-related equipment - Test methods for laser-induced damage threshold -
Part 1: Definitions and general principles (ISO 21254-1:2025)
Laser und Laseranlagen - Prüfverfahren für die laserinduzierte Zerstörschwelle - Teil 1:
Begriffe und allgemeine Grundsätze (ISO 21254-1:2025)
Lasers et équipements associés aux lasers - Méthodes d'essai du seuil
d'endommagement provoqué par laser - Partie 1: Définitions et principes de base (ISO
21254-1:2025)
Ta slovenski standard je istoveten z: EN ISO 21254-1:2025
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 21254-1
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2025
EUROPÄISCHE NORM
ICS 31.260 Supersedes EN ISO 21254-1:2011
English Version
Lasers and laser-related equipment - Test methods for
laser-induced damage threshold - Part 1: Definitions and
general principles (ISO 21254-1:2025)
Lasers et équipements associés aux lasers - Méthodes Laser und Laseranlagen - Prüfverfahren für die
d'essai du seuil d'endommagement provoqué par laser laserinduzierte Zerstörschwelle - Teil 1: Begriffe und
- Partie 1: Définitions et principes de base (ISO 21254- allgemeine Grundsätze (ISO 21254-1:2025)
1:2025)
This European Standard was approved by CEN on 27 July 2025.

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.

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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
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 21254-1:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 21254-1:2025) 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 March 2026, and conflicting national standards shall
be withdrawn at the latest by March 2026.
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 21254-1:2011.
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 21254-1:2025 has been approved by CEN as EN ISO 21254-1:2025 without any
modification.
International
Standard
ISO 21254-1
Second edition
Lasers and laser-related
2025-08
equipment — Test methods for
laser-induced damage threshold —
Part 1:
Definitions and general principles
Lasers et équipements associés aux lasers — Méthodes d'essai du
seuil d'endommagement provoqué par laser —
Partie 1: Définitions et principes de base
Reference number
ISO 21254-1:2025(en) © ISO 2025

ISO 21254-1:2025(en)
© ISO 2025
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
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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
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 21254-1:2025(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Terms and definitions .2
3.2 Symbols and units of measurement.3
4 Units of laser irradiation, LIDT and pertinent units . 4
5 Laser damage, damage threshold and associated criteria . 4
5.1 General laser damage criteria .4
5.1.1 General .4
5.1.2 Classical criterion of laser-induced damage .5
5.1.3 Functional criterion of laser-induced damage .5
5.1.4 Failure mode.5
5.1.5 Laser-induced damage threshold (LIDT) .5
5.1.6 Functional laser-induced damage threshold (F-LIDT) .5
5.1.7 Method of damage threshold calculation .5
5.2 Techniques of laser damage interrogation and related terms .5
5.2.1 General .5
5.2.2 Classical 1-on-1 test .6
5.2.3 Classical S-on-1 test .6
5.2.4 Functional R(S)-on-1 test .6
5.2.5 Functional raster scan test.6
5.2.6 Acceptance test “pass-fail” .6
5.2.7 Laser-induced fatigue .6
5.2.8 Characteristic damage curve or fatigue curve .6
5.2.9 Laser-induced conditioning .6
5.2.10 Conditioning curve .7
5.3 Parameters of testing, sampling and reporting .7
5.3.1 Typical pulse .7
5.3.2 Laser irradiation level, L .7
5.3.3 Maximum irradiation dose .7
5.3.4 Applied irradiation dose .7
5.3.5 Target plane .7
6 Sampling . 7
7 Test methods . 8
7.1 Principle .8
7.2 Apparatus .9
7.2.1 Laser .9
7.2.2 Variable attenuator and beam delivery system .9
7.2.3 Focusing system.9
7.2.4 Specimen holder .10
7.2.5 Damage detection and inspection systems .10
7.2.6 Beam diagnostic unit .10
7.3 Preparation of specimens for testing . 13
7.4 Procedure .14
8 Accuracy of peak irradiation level .15
8.1 General . 15
8.2 Relative standard deviation of peak fluence . 15
8.3 Relative standard deviation of peak irradiance . 15
8.4 Relative standard deviation of linear power density .16
8.5 Relative standard deviation of average peak irradiance .16

iii
ISO 21254-1:2025(en)
9 Test report . 17
Annex A (normative) General usage notes . 19
Bibliography .29

iv
ISO 21254-1:2025(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 document 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 ISO/TC 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 second edition cancels and replaces the first edition (ISO 21254-1:2011) which has been technically
revised.
The main changes are as follows:
— functional damage criteria and functional damage threshold (F-LIDT) are introduced;
— new units of laser irradiation level are introduced;
— two new test protocols are introduced:
— extension to R(S)-on-1 test;
— extension to the raster scan test;
— integration of a new section “General usage notes” in Annex A;
— discussion on accuracy of measurement units is extended.
A list of all parts in the ISO 21254 series can be found on the ISO website.
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.

v
ISO 21254-1:2025(en)
Introduction
Optical components are irreversibly damaged above the so-called laser-induced damage threshold
(otherwise referred to as LIDT or damage threshold): which is the maximum laser irradiation level at which
it is expected that there is zero probability of damage. Below the single-shot damage threshold, a delayed
damage event might also develop over time as a consequence of repetitive laser irradiation, the so-called
fatigue effect. Alternatively, repeated exposure with increasing laser irradiation can cause an increase in
the damage threshold; the so-called conditioning effect. For the vast majority of use cases, the damage tends
to develop on optical surfaces. Only on specific occasions will it occur within the bulk. Thus, if not requested
or declared otherwise, the laser-induced damage threshold is tested and reported for the entrance surface of
the optical component. For optics with high transmittance, damage may first develop at the exit surface or in
the bulk without observing a damage of the entrance surface due to radiation field enhancement effects: self-
focusing, diffraction or interference with back-reflected radiation. Back surface damage might also feature
lower damage thresholds than the entrance surface as a consequence of poor optical quality. In such cases a
functional damage threshold testing can be conducted for the exit surface. However, focusing conditions and
the functional damage criterion need to be documented in the test report. Environmental contamination by
airborne particles, volatile organic compounds, vacuum exposure, and technological imperfections such as
nodular defects of coatings, polishing scratches, Beilby layer, sub-surface damage as well as bulk inclusions,
dislocations, or inhomogeneities of any other type are also known to affect the performance of an optical
component.
[6-64]
Due to a variety of possible failure mechanisms , the experimentally estimated “damage threshold”
is an aggregated feature of optics handling, environmental conditions, material and surface preparation
techniques as well as laser-related exposure parameters such as wavelength, spot size, repetition rate, and
pulse duration. As a consequence, there is no single procedure, that could universally satisfy all the testing
needs for all the types of optical components available. Instead, different damage testing strategies evolved
to address particular needs for testing. Various parts of this document are concerned with the determination
of irreversible damage of the optical surfaces and the bulk of an optical component under the influence of
laser exposure. This document is dedicated to the fundamentals and general principles of the measurement
of laser-induced damage thresholds. Based on the apparatus outlined in ISO 21254-1, measurement
protocols for damage testing (1-on-1, S-on-1, R(S)-on-1, and Raster scan) are described in ISO 21254-2, and
acceptance testing is described in ISO 21254-3. Recommendations and associated risks pertinent to distinct
test procedures will be discussed in more detail in Annex A.
The “classical” 1-on-1 test is a damage threshold measurement procedure that uses one pulse of laser
irradiation on each unexposed test site of the specimen. In contrast, the “classical” S-on-1 measurement
program is based on a series of pulses with a constant laser irradiation level applied to each unexposed
site of the specimen. Testing with multiple laser pulses is closer to the operational conditions in the field,
however, the experimental effort necessary for S-on-1 tests is also significantly higher. The ISO 21254-series
also introduce new alternatives – concept of “functional” damage threshold and new testing protocols such
as R(S)-on-1 and Raster scan. In an R(S)-on-1 test, the same test site is irradiated with sequences of (S)
pulses while gradually increasing the irradiation level between particular irradiations until the damage is
observed. As a further extension of this measurement concept, the Raster scan technique is designed to
irradiate a significant fraction of the test sample area with spatially overlapping laser pulses. ISO 21254-3
describes the acceptance testing for a certain laser irradiation level of optical surfaces, leaving samples that
pass the test undamaged. ISO/TR 21254-4, which considers damage detection methods and the inspection
of tested surfaces, is a Technical Report which complements this document.

vi
International Standard ISO 21254-1:2025(en)
Lasers and laser-related equipment — Test methods for laser-
induced damage threshold —
Part 1:
Definitions and general principles
WARNING — Laser exposure of toxic materials (e.g. ZnSe, GaAs, CdTe, ThF , chalcogenides, Be, Cr, Ni)
can lead to serious health hazards such as toxic fumes.
WARNING — Laser damage threshold testing involves 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 defines terms used in conjunction with, and the general principles of, test methods for
determining the laser-induced damage threshold and for the assurance of optical laser components subjected
to laser radiation.
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 11146-1, Lasers and laser-related equipment — Test methods for laser beam widths, divergence angles and
beam propagation ratios — Part 1: Stigmatic and simple astigmatic beams
ISO 11146-2, Lasers and laser-related equipment — Test methods for laser beam widths, divergence angles and
beam propagation ratios — Part 2: General astigmatic beams
ISO 21254-2, Lasers and laser-related equipment — Test methods for laser-induced damage threshold — Part 2:
Threshold determination
ISO 21254-3, Lasers and laser-related equipment — Test methods for laser-induced damage threshold — Part 3:
Assurance of laser power (energy) handling capabilities
3 Terms and definitions
For this document, the terms and definitions given in ISO 11145 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/

ISO 21254-1:2025(en)
3.1 Terms and definitions
3.1.1
peak fluence
H
AOI adjusted radiant energy per effective area of the typical pulse
Qcos()α
H = (1)
A
T,eff
Note 1 to entry: The cosine of the angle of incidence addresses the elongation of effective beam in the projected
target plane.
3.1.2
peak irradiance
I
AOI adjusted radiant energy per effective pulse duration per effective area of the typical pulse
Qcos α
H ()
I == (2)
τ A τ
effT,eff eff
3.1.3
peak linear power density
F
AOI adjusted average power of laser irradiation per effective beam diameter
P cos α
()
av
F = (3)
d
T,eff
3.1.4
average peak irradiance
E
AOI adjusted average radiant laser power per time-averaged effective area:
P cos α
()
av
E = (4)
A
T,eff
3.1.4.1
effective area
A
T,eff
ratio of total pulse energy to peak fluence (3.1.1) in the target plane at normal incidence:
Q
A = (5)
T,eff
H
Note 1 to entry: The subscript T indicates the target plane (see 5.3.5) as a reference at normal incidence.
3.1.4.2
time averaged effective area
A
T,eff
ratio of the average power P and the time-averaged peak irradiance
av
E at normal incidence
P
av
A = (6)
T,eff
E
ISO 21254-1:2025(en)
3.1.5
effective beam diameter
d
T,eff
diameter of the effective area (3.1.4.1) or time averaged effective area (3.1.4.2) given by twice the square root
of the effective area (3.1.4.1) or time averaged effective area (3.1.4.2) divided by π
A
T,eff
d =2 (7)
T,eff
π
3.1.6
effective pulse duration
τ
eff
ratio of pulse energy to radiant peak power
Q
τ = (8)
eff
P
pk
3.2 Symbols and units of measurement
The symbols and units of measurement used are the following:
Symbol Unit Term
λ nm wavelength
α rad angle of incidence (AOI)
p type and degree of polarization: linear (s or p), circular, elliptical, random
d cm beam diameter (peak/e level - for Gaussian beams only) at normal incidence
T
d cm effective beam diameter in the target plane at normal incidence
T,eff
A cm effective area of typical laser pulse in the target plane at normal incidence
T,eff
time-averaged effective area in the target plane corresponding to laser burst at
cm
A
T,eff
normal incidence
time- averaged numerical value of most intense pixel (or equivalent area in
scanning devices - the product of the scanning step and the distance between
E W/cm scan lines) within the beam profile taken by a radiation-sensitive array for
max
continuous wave (CW) or burst of quasi continuous wave (quasi-CW) laser
a
irradiation in the target plane at normal incidence
the total irradiated area per test, adjusted for the angle of incidence (AOI),
A cm encompassing all exposed but undamaged test sites where the irradiation level
C
is between C% and 100 % of the lowest observed damage (LOD)
τ s pulse duration at full width of half maximum (FWHM)
FWHM
τ s effective pulse duration
eff
f Hz pulse repetition rate
p
Q J pulse radiant energy
P W peak radiant power
pk
P W average radiant power
av
H J/cm peak fluence, AOI-adjusted
E W/cm average peak irradiance, AOI-adjusted
F W/cm peak linear power density, AOI-adjusted
I W/cm peak irradiance, AOI-adjusted
the value of the most intense pixel taken by a radiation-sensitive array (or
H J/cm equivalent area scanning step × scan line spacing for scanning devices) in the
max
a
target plane of a single-pulse beam profile at normal incidence

ISO 21254-1:2025(en)
Symbol Unit Term
the value of the most intense pixel taken by a radiation-sensitive array (or
E W/cm equivalent area scanning step × scan line spacing for scanning devices) in the
max
a
target plane of a CW laser irradiation profile at normal incidence
H J/cm threshold fluence measured at normal incidence
th, norm
E W/cm threshold average irradiance measured at normal incidence
th, norm
F W/cm threshold linear power density measured at normal incidence
th, norm
I W/cm threshold irradiance measured at normal incidence
th, norm
N minimum number of laser pulses required to cause damage
min
t s time to failure – minimum exposure time required to cause damage
TTF
pulse count (or time the maximum number of pulses (or exposure time) per laser irradiation level
S
count) site
N site count total number of sites for the test
ts
the area of one sensor pixel, or for scanning devices, the product of the scan-
A cm ning step and the distance between scan lines, representing an equivalent
pix
area.
a
The definitions above assume that sensor or scan pixels or equivalent area in scanning devices - the product of
the scanning step and the distance between scan lines - are calibrated to absolute units of fluence or irradiance. De-
pending on the instrument employed for the measurement of the beam profile other (relative) units as for example
“bit counts” are often used for the measurement values H and E . For details, see 7.2.6.3.
bit,max bit,max
4 Units of laser irradiation, LIDT and pertinent units
Depending on the laser irradiation type in a field application, select the most appropriate unit(s) for defining
LIDT in accordance with A.4:
— peak fluence, H;
— peak irradiance, I;
— peak linear radiant power density, F;
— average peak irradiance, E.
NOTE As a consequence of the historical development of laser technology, alternative terms for laser irradiation
are often used in the field. In this context, the term “energy density” or “radiance exposure” (in ISO 11145) are often
assigned to the applied radiant energy per unit area (in units of J/cm ), and the term “intensity” is often used for
applied radiant power per unit area (in units of W/cm ). In view of the specific damage mechanisms and their scaling
laws related to cw-irradiation, the term “linear power density” is used in ISO 21254 series, which denotes the linear
radiant power density (in units of W/cm). To harmonize the terms and definitions, the term “fluence” designating the
radiant energy per unit area and “irradiance” designating the radiant power per unit area are used in this document.
When irradiating the target plane at an angle of incidence, α, other than 0 radians, the cosine factor shall be
included in the calculation of the laser irradiation level to account for the elongation of the effective beam.
5 Laser damage, damage threshold and associated criteria
5.1 General laser damage criteria
5.1.1 General
The estimated damage threshold is highly dependent on the chosen damage criterion (detection technique
and its sensitivity level) as well as the test protocol and total interrogated area per test. By considering the
large variety of known damage detection techniques and interrogation methods, a clear distinction between
classical and functional damage threshold shall be made when reporting test results.

ISO 21254-1:2025(en)
5.1.2 Classical criterion of laser-induced damage
Any permanent laser-induced change or modification of the exposed region (either surface or bulk) that is
apparent by using a differential interference contrast (DIC) microscopy technique.
A microscope objective with a magnification of ×10 (at least NA = 0,25 or better) shall be used in conjunction
with a suitable imaging system or ocular lens to give a minimum magnification of ×150 for classical damage
testing. A DIC apparent laser-induced change is considered as a “damage”; non-apparent change - “no
damage”.
5.1.3 Functional criterion of laser-induced damage
Any observable or measurable (permanent or reversible) laser-induced change in the functional performance
of the optic, which can be recorded by an online or offline monitoring technique, relevant to the intended
end use application.
5.1.4 Failure mode
Nature of a specific physical mechanism or sequence of interrelated phenomena by which laser-induced
damage (failure) occurs.
5.1.5 Laser-induced damage threshold (LIDT)
LIDT estimated via classical 1-on-1 or S-on-1 interrogation method as highest quantity of laser irradiation
incident upon the optical component featuring zero probability of damage according to classical criterion
of damage.
5.1.6 Functional laser-induced damage threshold (F-LIDT)
F-LIDT is defined as the highest estimated quantity of laser irradiation incident upon the optical component
with no deterioration according to a user-defined functional criterion of damage, specific to end use
application (see Annex A for details).
5.1.7 Method of damage threshold calculation
Depending on the nature of dominant laser damage and chosen interrogation technique, the appropriate
method should be used to rate damage thresholds:
a) damage probability method:
highest irradiation level featuring zero extrapolated probability of damage for failure modes with non-
deterministic damage statistics;
b) HBFD average method:
average of two laser irradiation levels, namely “Highest Before-Damage“ and “First-Damaged” or
“Lowest Observed Damage” irradiation level for failure modes featuring deterministic damage effects
or tests routines where the damage probability is not directly measured.
5.2 Techniques of laser damage interrogation and related terms
5.2.1 General
There are three fundamental types of damage testing, namely “classical”, “functional” and “acceptance
test”. 1-on-1 and S-on-1 tests determine “classical damage thresholds” - LIDT; functional tests are used to
determine thresholds of functional optics performance – F-LIDT; acceptance tests are used to qualify optics
for a particular application.
ISO 21254-1:2025(en)
5.2.2 Classical 1-on-1 test
Test protocol that interrogates multiple, well spatially separated test sites of the test sample, each with a
single laser pulse irradiation so that the probability of damage can be estimated as a function of the laser
irradiation level (involving transition region from 0 % to 50 % or higher).
5.2.3 Classical S-on-1 test
Test protocol that interrogates multiple, well spatially separated test sites with a maximum of S laser shots
per site. Multiple test sites are irradiated for each laser irradiation level so that the dose (time or pulses)
required to initiate damage is recorded for the given irradiation level and test site. The probability of damage
is then estimated within each pulse class of interest involving the transition from 0 % to 50 % or higher.
5.2.4 Functional R(S)-on-1 test
Test protocol that interrogates one or multiple test sites with a laser irradiation level that increases stepwise.
The laser irradiation level is increased either linearly or nonlinearly until a damage event is detected or
the maximum irradiation level of the system is reached; either a single pulse or multiple pulses (S) can be
applied for every irradiation level.
5.2.5 Functional raster scan test
Test protocol that involves scanning of a predefined test area of the sample with space-overlapped laser
irradiation so that the specified irradiation level coverage (for example 90 % of peak value) is ensured within
the entire scan area. The laser irradiation level is increased either linearly or nonlinearly until a damage
event is detected or the maximum irradiation level of the system is reached; the test area is inspected for
defects before the test and for damage after (or during) every new scan.
5.2.6 Acceptance test “pass-fail”
Test protocol that involves an exposure of test sample with a well-specified peak irradiation level, predefined
exposure time, and test area corresponding to realistic irradiation conditions of the intended application (on
either single or multiple test sites or predefined scan area). The sample is inspected before and after the test.
If no damage is observed, the optical element passes the test and is qualified for its intended application.
5.2.7 Laser-induced fatigue
Decrease of laser power (energy) handling capability of the test sample due to prolonged repetitive laser
irradiation at fixed irradiation level leading to limited lifetime.
NOTE Repetitive laser exposure below the single-shot (1-on-1) damage threshold can sometimes lead to time-
delayed damage events. Fatigue can be expressed quantitatively as a ratio between S-on-1 and 1-on-1 damage
thresholds. See also laser-induced conditioning.
5.2.8 Characteristic damage curve or fatigue curve
Laser-induced damage threshold expressed as a function of laser irradiation dose (either in pulses or time).
NOTE Characteristic damage curve is also known as fatigue curve or S-N curve.
5.2.9 Laser-induced conditioning
Increase of laser power (energy) handling capability of the test sample due to repetitive and gradually
increasing laser irradiation level over previously exposed test site or area.
NOTE The effect can be expressed quantitatively as a ratio between R(S)-on-1 and 1-on-1 damage thresholds. See
also laser-induced fatigue.
ISO 21254-1:2025(en)
5.2.10 Conditioning curve
Graphical representation of either linear or nonlinear ramping or laser pre-irradiation history over the test
site or area prior functional damage is achieved.
NOTE Graphical markers, indicating F-LIDT (R(S)-on-1; raster scan) and reference LIDT (1-on-1) and damaging
levels can be added to the conditioning graph to visualize conditioning effects.
5.3 Parameters of testing, sampling and reporting
5.3.1 Typical pulse
Laser pulse with temporal and spatial shapes that represent the average properties of pulses in a pulse train
(burst) or CW irradiation.
5.3.2 Laser irradiation level, L
Quantity expressed in units of laser irradiation per typical pulse, that is used to expose the test site or scan
area. The laser irradiation level is typically varied during testing when interrogating specimen(s). For multi-
pulse or CW irradiation, the laser irradiation level is always bound to the total irradiation dose (expressed in
applied laser pulses or exposure time).
5.3.3 Maximum irradiation dose
Maximum amount of laser irradiation applied to a single test site for a chosen laser irradiation level in case
of no detected damage.
NOTE The amount of laser irradiation is typically expressed as total laser energy applied, however for practical
reasons it can also be represented in form of applied laser pulses or duration of continuous exposure time in
combination with the chosen units of laser irradiation level.
5.3.4 Applied irradiation dose
Amount of irradiation applied to single test site for a chosen laser irradiation level until the moment of
detected damage.
NOTE For repetitively pulsed irradiation, N is the number of incident laser pulses required to cause detectable
min
damage; for CW or quasi-CW irradiation, t is the time to failure of the time required to cause detectable damage.
TTF
5.3.5 Target plane
Plane tangential to the surface of the specimen at the point of intersection of the test laser beam axis with
the surface of the specimen.
NOTE For curved surfaces more than one target plane might be required to perform damage testing.
6 Sampling
For testing coated parts, either an actual part or a witness specimen may be chosen. If a witness specimen
is chosen for testing, the substrate material and surface finish shall be identical to that of the actual part.
In cases when test parts are coated, witness specimens shall be coated during the same coating run as the
actual part. The coating run number and date shall be identified for the specimen. In the case of a non-
uniform thickness distribution within the coating chamber, the position of the witness sample shall be well-
defined and documented to represent the coating run, in accordance with A.1.1.
Furthermore, samples should be handled and packed with care in a dust-free environment to avoid any
possible contamination before testing. It is recommended to protect optical surfaces from exposure to any
item that could cause particle or chemical contamination.

ISO 21254-1:2025(en)
7 Test methods
7.1 Principle
The fundamental arrangement for laser damage testing is depicted in Figure 1. The output of a well-
characterized, stable laser source is adjusted to the desired maximu
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