SIST EN ISO 21254-1:2011
(Main)Lasers and laser-related equipment - Test methods for laser-induced damage threshold - Part 1: Definitions and general principles (ISO 21254-1:2011)
Lasers and laser-related equipment - Test methods for laser-induced damage threshold - Part 1: Definitions and general principles (ISO 21254-1:2011)
This part of ISO 21254 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.
Laser und Laseranlagen - Prüfverfahren für die laserinduzierte Zerstörschwelle - Teil 1: Begriffe und allgemeine Grundsätze (ISO 21254-1:2011)
Die vorliegende Norm ist ein Teil von ISO 21254 und legt die Begriffe und allgemeinen Grundsätze von
Prüfverfahren zur Bestimmung der laserinduzierten Zerstörschwelle und Belastbarkeit von optischen, mit
Laserstrahlung beanspruchten Laserkomponenten fest.
Lasers et équipements associés aux lasers - Méthodes d'essai du seuil d'endommagement provoqué par laser - Partie 1: Définitions et principes de base (ISO 21254-1:2011)
L'ISO 21254-1:2011 définit les termes et les principes de base des méthodes d'essai permettant de déterminer le seuil d'endommagement provoqué par laser et de vérifier les composants optiques du laser soumis à un rayonnement laser.
Laserji in z laserji povezana oprema - Preskusne metode za ugotavljanje praga poškodbe, povzročene z laserjem - 1. del: Definicije in splošna načela (ISO 21254-1:2011)
Ta del ISO 21254 določa izraze in splošna načela, ki se uporabljajo skupaj s preskusnimi metodami za ugotavljanje praga poškodb, povzročenih z laserjem, in za zagotovitev komponent optičnega laserja, izpostavljenih sevanju laserja.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 21254-1:2011
01-oktober-2011
1DGRPHãþD
SIST EN ISO 11254-1:2000
SIST EN ISO 11254-2:2002
SIST EN ISO 11254-2:2002/AC:2003
/DVHUMLLQ]ODVHUMLSRYH]DQDRSUHPD3UHVNXVQHPHWRGH]DXJRWDYOMDQMHSUDJD
SRãNRGEHSRY]URþHQH]ODVHUMHPGHO 'HILQLFLMHLQVSORãQDQDþHOD ,62
Lasers and laser-related equipment - Test methods for laser-induced damage threshold -
Part 1: Definitions and general principles (ISO 21254-1:2011)
Laser und Laseranlagen - Prüfverfahren für die laserinduzierte Zerstörschwelle - Teil 1:
Begriffe und allgemeine Grundsätze (ISO 21254-1:2011)
Lasers et équipements associés aux lasers - Méthodes d'essai du seuil
d'endommagement provoqué par laser - Partie 1: Définitions et principes de base (ISO
21254-1:2011)
Ta slovenski standard je istoveten z: EN ISO 21254-1:2011
ICS:
31.260 Optoelektronika, laserska Optoelectronics. Laser
oprema equipment
SIST EN ISO 21254-1:2011 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 21254-1:2011
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SIST EN ISO 21254-1:2011
EUROPEAN STANDARD
EN ISO 21254-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
July 2011
ICS 31.260 Supersedes EN ISO 11254-1:2000, EN ISO 11254-2:2001
English Version
Lasers and laser-related equipment - Test methods for laser-
induced damage threshold - Part 1: Definitions and general
principles (ISO 21254-1:2011)
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 21254-1:2011)
1:2011)
This European Standard was approved by CEN on 14 July 2011.
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, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2011 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 21254-1:2011: E
worldwide for CEN national Members.
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SIST EN ISO 21254-1:2011
EN ISO 21254-1:2011 (E)
Contents Page
Foreword .3
2
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SIST EN ISO 21254-1:2011
EN ISO 21254-1:2011 (E)
Foreword
This document (EN ISO 21254-1:2011) 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 January 2012, and conflicting national standards shall be withdrawn at
the latest by January 2012.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 11254-1:2000, EN ISO 11254-2:2001.
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, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 21254-1:2011 has been approved by CEN as a EN ISO 21254-1:2011 without any
modification.
3
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SIST EN ISO 21254-1:2011
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SIST EN ISO 21254-1:2011
INTERNATIONAL ISO
STANDARD 21254-1
First edition
2011-07-15
Lasers and laser-related 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 21254-1:2011(E)
©
ISO 2011
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SIST EN ISO 21254-1:2011
ISO 21254-1:2011(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2011
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2011 – All rights reserved
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SIST EN ISO 21254-1:2011
ISO 21254-1:2011(E)
Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.1
3 Terms and definitions .2
4 Symbols and units of measurement.3
5 Sampling.4
6 Test methods .4
6.1 Principle.4
6.2 Apparatus.5
6.3 Preparation of specimens.10
6.4 Procedure.10
7 Accuracy.11
8 Test report.11
Annex A (informative) Units and scaling of laser-induced damage thresholds.13
Bibliography.14
© ISO 2011 – All rights reserved iii
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SIST EN ISO 21254-1:2011
ISO 21254-1:2011(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 21254-1 was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee SC 9,
Electro-optical systems.
This first edition of ISO 21254-1:2011, together with ISO 21254-2:2011, cancels and replaces
ISO 11254-1:2000 and ISO 11254-2:2001, which have been technically revised.
ISO 21254 consists of the following parts, under the general title Lasers and laser-related equipment — Test
methods for laser-induced damage threshold:
⎯ Part 1: Definitions and general principles
⎯ Part 2: Threshold determination
⎯ Part 3: Assurance of laser power (energy) handling capabilities
⎯ Part 4: Inspection, detection and measurement [Technical Report]
iv © ISO 2011 – All rights reserved
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SIST EN ISO 21254-1:2011
ISO 21254-1:2011(E)
Introduction
Optical components can be damaged by laser irradiation of sufficiently high energy or power. At any specified
laser irradiation level and operation mode of the laser source, the probability for laser damage is usually
higher for the surface of a component than for the bulk. Thus, the limiting value of an optical component is
frequently given by the damage threshold of its surface which might be coated to influence the optical
properties. Bulk damage is observed if the electrical field strength in the bulk of the component is enhanced by
self-focusing, interference, scattering or other effects. Also, imperfections, such as inclusions, dislocations,
colour centres or inhomogeneities, can reduce the power-handling capability in the bulk of an optical
component. Damage by single laser pulses is often induced by defects or mechanical stress in the coating,
contamination of the surface, or optical absorption, leading to catastrophic heating of the surface. For multiple-
pulse operation, not only reversible mechanisms induced by thermal heating and distortion but also
irreversible damage mechanisms induced by ageing, microdamage, moisture damage and generation or
migration of defects are observed. The various parts of this International Standard are concerned with the
determination of irreversible damage of the optical surfaces and the bulk of an optical component under the
influence of a laser beam. Depending on the environmental conditions, damage is a function of the material
properties and the laser parameters, in particular wavelength, spot size and irradiation duration.
This part of ISO 21254 is dedicated to the fundamentals and general principles of the measurement of laser-
induced damage thresholds (LIDTs). On the basis of the apparatus and measurement protocols described in
ISO 21254-1, ISO 21254-2 and ISO 21254-3, this part of ISO 21254 outlines procedures for damage testing
under different conditions. The protocols for the determination of the 1-on-1 and S-on-1 damage thresholds
are described in ISO 21254-2. The 1-on-1 test is a damage threshold measurement procedure that uses one
shot of laser radiation on each unexposed site on the specimen surface. In contrast to this, the S-on-1
measurement programme is based on a series of pulses with constant energy density applied to each
unexposed site of the specimen surface. This test reflects the operational conditions of the sample in typical
applications but, compared to the 1-on-1 measurement protocol, the experimental effort necessary for S-on-1
tests is significantly higher. ISO 21254-3 concentrates on the assurance of the power or energy density
handling capability 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 ISO 21254-1.
© ISO 2011 – All rights reserved v
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SIST EN ISO 21254-1:2011
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SIST EN ISO 21254-1:2011
INTERNATIONAL STANDARD ISO 21254-1:2011(E)
Lasers and laser-related equipment — Test methods for laser-
induced damage threshold —
Part 1:
Definitions and general principles
WARNING — The extrapolation of damage data can lead to an overestimation of the laser-induced
damage threshold. In the case of toxic materials (e.g. ZnSe, GaAs, CdTe, ThF , chalcogenides, Be,
4
Cr, Ni), this can lead to serious health hazards. See Annex A for further comments.
1 Scope
This part of ISO 21254 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 referenced documents are indispensable for the application 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 10110-7, Optics and photonics — Preparation of drawings for optical elements and systems — Part 7:
Surface imperfection tolerances
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
ISO/TR 21254-4, Lasers and laser-related equipment — Test methods for laser-induced damage threshold —
Part 4: Inspection, detection and measurement
© ISO 2011 – All rights reserved 1
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SIST EN ISO 21254-1:2011
ISO 21254-1:2011(E)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 11145 and the following apply.
3.1
surface damage
any permanent laser-radiation-induced change in the characteristics of the surface of the specimen which can
be observed by an inspection technique and at a sensitivity related to the intended operation of the product
concerned
NOTE Damage may occur on the front surface or the rear surface of the optical component. The damage threshold
value for the front surface may differ from that for the rear surface.
3.2
bulk damage
any permanent laser-radiation-induced change in the characteristics of the bulk of the specimen which can be
observed by an inspection technique and at a sensitivity related to the intended operation of the product
concerned
3.3
1-on-1 test
test programme that uses one shot of laser radiation on each unexposed site on the specimen surface
3.4
linear power density
F
th
linear power density threshold, expressed in watts per centimetre (W/cm), above which damage might occur
NOTE The linear power density is applicable for cw and long-pulse operation. For laser damage considerations, a
1/2
long pulse is assumed when the thermal transit distance (2Dτ ) , where D is the thermal diffusivity, is of the same order
eff
of size as the test spot diameter d .
T,eff
3.5
S-on-1 test
test programme that uses a series of pulses with constant energy density on each unexposed site with a short
and constant time interval between two successive pulses, where the length of the time interval between the
pulses of a series is given by the reciprocal of the pulse repetition rate of the laser source
3.6
number of shots per interrogation site
S
number of pulses in a pulse train used in an S-on-1 test
3.7
threshold
highest quantity of laser radiation incident upon the optical component for which the extrapolated probability of
damage is zero, where the quantity of laser radiation may be expressed as energy density H , power density
th
E , or linear power density F
th th
3.8
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
3.9
effective area
A
T,eff
ratio of pulse energy to maximum energy density of the laser pulse in the target plane
NOTE For spatial beam profiling perpendicular to the direction of beam propagation and for angles of incidence
differing from 0 rad, the cosine of the angle of incidence is included in the calculation of the effective area.
2 © ISO 2011 – All rights reserved
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SIST EN ISO 21254-1:2011
ISO 21254-1:2011(E)
3.10
effective beam diameter
d
T,eff
double the square root of the effective area divided by π:
A
T,eff
d = 2 (1)
T,eff
π
3.11
effective pulse duration
τ
eff
ratio of pulse energy to peak pulse power of the pulse
3.12
typical pulse
pulse with temporal and spatial shapes that represent the average properties of the pulses forming a pulse
series used in an S-on-1 test
3.13
minimum number of pulses
N
min
number of incident pulses necessary to cause detectable damage
3.14
characteristic damage curve
representation of the S-on-1 laser-induced damage threshold as a function of the number of pulses per site at
a specified pulse repetition rate
4 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
p degree of polarization
d mm beam diameter in the target plane
T
d mm effective beam diameter in the target plane
T,eff
2
A cm effective area in the target plane
T,eff
τ s pulse duration
H
τ s effective pulse duration
eff
f Hz pulse repetition rate
p
P W average power
av
Q J pulse energy
F W/cm maximum linear power density
max
2
E W/cm maximum power density
max
2
H J/cm maximum energy density
max
P W peak pulse power
pk
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SIST EN ISO 21254-1:2011
ISO 21254-1:2011(E)
2
E W/cm threshold power density
th
F W/cm threshold linear power density
th
2
H J/cm threshold energy density
th
N minimum number of pulses causing damage
min
S number of shots per interrogation site
N total number of sites for the test
ts
5 Sampling
For testing, either an actual part or a witness specimen may be chosen. If a witness specimen is tested, the
substrate material and surface finish shall be the same as for the actual part. In the case of a coated sample,
the witness specimen shall be coated in the same coating run as the actual part. The coating run number and
date shall be identified for the specimen. If bulk damage is expected, the substrate material of the test
component shall be identical to that of the actual part.
6 Test methods
6.1 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 pulse energy or cw-power by a variable
attenuator and delivered to the specimen located at or near the focus of a focusing system.
The specimen is mounted in a manipulator which is used to position different test sites in the beam and to set
the angle of incidence. The polarization state is set with an appropriate waveplate. The incident laser beam is
sampled with a beam splitter that directs a portion of the laser energy to a beam diagnostic unit. The beam
diagnostic unit permits simultaneous determination of the total pulse energy and the spatial and temporal
profiles.
Key
1 laser system
2 variable attenuator
3 waveplate
4 focusing system
5 beam diagnostic unit
6 online damage detector
7 specimen compartment
Figure 1 — Basic approach to laser damage testing
4 © ISO 2011 – All rights reserved
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SIST EN ISO 21254-1:2011
ISO 21254-1:2011(E)
The specimen is positioned at a defined location with reference to the laser beam at the specified angle of
incidence. Depending on the requirements of the test, test sites on the specimen are irradiated with single
laser pulses or with trains of pulses of constant energy density at a constant repetition rate. The specimen is
mounted in a holder. Each separate irradiation test is conducted without moving the specimen in the beam. It
is recommended that the distance between the test sites be greater than three times the laser spot diameter
d . For reliable tests, a sufficient number of test sites shall be tested at specific energy densities or power
T
densities. The determination of the damage threshold is based on the entire data set acquired during the
complete test and not on the state of damage at any individual site.
This procedure is applicable to testing with cw-lasers and pulsed laser systems irrespective of pulse length,
repetition rate, and wavelength.
2
Damage thresholds of pulsed lasers are usually expressed in units of energy density (J/cm ). The pulse
duration of the test laser shall be documented in the test report. Damage thresholds of cw-lasers are usually
expressed in terms of units of linear power density (W/cm). The power density is taken as the average power
during the irradiation time. Examples of units used for laser-induced damage thresholds are given in Annex A.
For pulsed lasers, any possible pulse repetition rate is permitted in conjunction with a specified pulse duration.
The pulse duration and the pulse repetition rate of the test laser shall be documented in the test report.
Laser-induced damage threshold values are dependent on the operating parameters of the laser system
employed for testing. For a comparison of threshold data under slightly different operating conditions, scaling
laws which are based on modelling of experimental data may be used. Safety aspects should be considered
for the application of scaling laws to hazardous materials.
6.2 Apparatus
The test facility consists of individual sections with specific functions.
6.2.1 Laser
A laser delivering a beam with a reproducible Gaussian or flat-top spatial profile (in accordance with
ISO 11146-1 and ISO 11146-2) is required. The temporal profile of the pulses is monitored during the
measurement. Pulses or pulse trains containing pulses whose maximum power density E varies by more
max
than 20 % shall be rejected. For S-on-1 tests the pulse repetition rate shall be constant within an error margin
of ±1 %. As a minimum specification of a laser system for damage testing, the pulse-to-pulse variation of the
maximum power density shall be less than ±20 %. Stability criteria for the beam parameters shall be
determined and documented in an error budget.
Beam diagnostic unit packages for lasers operating in the femtosecond regime exhibit a significantly lower
accuracy than typical measurement systems for longer pulse durations. As a minimum specification for fs-
lasers, the measured percentage variation of the maximum power density shall not exceed ±25 %.
6.2.2 Variable attenuator and beam delivery system
The laser output shall be attenuated to the required level with a device that is free of drift in its transmittance
and imaging properties.
The beam delivery system and the attenuator shall not affect the properties of the laser beam in a manner
inconsistent with the tolerances given in 6.2.1. In particular, the polarization state of the laser beam shall not
be altered by the beam delivery system.
6.2.3 Focusing system
The arrangement of the focusing system should be suited to the specific requirements of the laser system and
to the intended beam profile in the target plane. The specific arrangement and the parameters of the focusing
system shall be documented in the test report. The specifications of the active area and the energy density
shall be referred to the location of the test surface. The effective area shall not be altered during the damage
threshold measurement procedure. The self-focusing or filamentation threshold in the test environment shall
not be exceeded.
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SIST EN ISO 21254-1:2011
ISO 21254-1:2011(E)
For Gaussian beams, it is advisable to select an aperture of the focusing system which amounts to not less
than three times the beam diameter at the entrance of the focusing system. A minimum effective f-number of
50 and a beam diameter in the target plane of not less than 0,8 mm are recommended. The target plane
should be located at or near the focal waist formed by the focusing system. For laser systems whose power
density is restricted for technical reasons (for example long-pulse lasers, cw-lasers and fs-lasers), the beam
diameter may be reduced, depending on the power density necessary, but not to a value less than 0,2 mm. In
such cases, the effective f-number may be reduced to a value below 50. For flat-top laser beams, it is
advisable to position the test surface in the image plane of a focusing system with a focal length >0,2 m that
forms an image of a suitable aperture in the optical path.
Coherence effects in specimens with parallel surfaces can occur and affect the measurement. These effects
should preferably be eliminated by appropriate techniques such as wedging or tilting of the specimen. The use
of a highly convergent beam is also a practical way of removing coherence effects in the specimen.
The Kerr effect can develop in the bulk of a substrate after a short propagation length and induce surface and
bulk damage. If bulk damage is expected, the specimen should be positioned at a location where the variation
in the beam radius along a beam path length corresponding to the total thickness of the sample is less than
3 %.
6.2.4 Specimen holder
The test station shall be equipped with a manipulator which allows precise placement of the test sites on the
specimen with an accuracy appropriate to the specimen size and the distance between the test sites.
The specimen holder shall allow the specimen to be removed from the specimen compartment and analysed
away from the laser apparatus, and then repositioned at exactly the same location.
6.2.5 Damage detection
Suitable inspection techniques shall be used for examination of the surfaces and the bulk of the optical
component before and after the test. The techniques used shall be described in the test report. The
inspections of the surface shall be carried out with an incident-light microscope having Nomarski-type
differential-interference contrast. A microscope objective with a magnification of 10× shall be used in
conjunction with a suitable imaging system or ocular lens. Detailed examples of specimen inspection are
given in ISO/TR 21254-4.
For damage test methods involving more than one pulse per test site, a suitable online damage detection
system shall be installed to evaluate the state of the surface under test. It is recommended that the online
damage detection system have a facility for cutting off subsequent pulses and for stopping the pulse counter
after detecting damage.
For online damage detection, any suitable technique may be used. Techniques suited to this purpose are, for
instance, online microscopic techniques, photoacoustic and photothermal detection, as well as scatter
measurements using a separate laser or radiation from the las
...
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