ISO 23701:2023

INTERNATIONAL ISO
STANDARD 23701
First edition
2023-04
Optics and photonics — Laser
and laser-related equipment
— Photothermal technique for
absorption measurement and
mapping of optical laser components
Optique et photonique — Lasers et équipements associés aux lasers
— Technique photothermique pour la mesure et la cartographie de
l'absorption des composants laser optiques
Reference number
© ISO 2023
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols used and units of measure .2
5 Test method . 2
5.1 Test principle . 2
5.1.1 General . 2
5.1.2 Photothermal lensing (TL) . 3
5.1.3 Photothermal deflection (PTD) . . 3
5.1.4 Rules for selecting reflected and transmitted photothermal detection
schemes . 3
5.2 Measurement arrangement and test equipment . 3
5.2.1 Photothermal detection arrangement . 3
5.2.2 Pump laser . 6
5.2.3 Probe laser . 6
5.2.4 Translation stage . 6
5.2.5 Detection unit . 7
5.2.6 Data acquisition and processing . 7
5.2.7 Environment . 7
5.3 Preparation of test sample . 7
6 Test procedure .7
6.1 General . 7
6.2 Measurements of photothermal amplitude and phase . 8
6.3 Maps of photothermal amplitude and phase . 8
6.4 Calibration of photothermal amplitude . 9
6.5 Assessments of the measurement . 10
7 Evaluation .11
7.1 Determination of absorption via photothermal measurement . 11
7.2 Determination of absorptance via photothermal calibration .12
7.3 Two-dimensional/three-dimensional maps of absorption .13
7.4 Mapping area and spatial resolution . 13
8 Test report .14
Annex A (informative) Theoretical and practical considerations on calibration .16
Annex B (informative) Separation of surface absorption and bulk absorption.18
Annex C (informative) Test report .21
Bibliography .22
iii
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
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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).
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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.
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
Introduction
With the rapid development of high-power/high-energy laser technology, laser-induced damage to
optical laser components and laser-induced thermal distortion in laser components become the most
important limiting factors for the operation and applications of high-power/high-energy laser systems.
Normally, the laser-induced damages to optical laser components are caused by absorbing defects
on the surface or within the laser components which result in thermal stress or melting of the laser
components and lead to damage. The thermal distortions, which induce wavefront distortions and
therefore beam quality deteriorations to the laser beam, are caused by non-uniform thermal expansion
or refractive index change due to absorption irregularities (such as absorbing defects) inside the laser
components. To improve the laser-induced damage threshold (LIDT) and reduce the laser-induced
thermal distortion of laser components used in high-power/high-energy laser systems, there are needs
not only to measure precisely the absorptance of the laser components, but also to detect various
absorbing defects on/within the laser components, therefore to improve the performance of these laser
components via optimizing fabrication/coating processes.
Currently, the ISO 11551 standardized testing method - laser calorimetry for absorptance measurements
of optical laser components can only measure test samples with small sizes (normally less than 50 mm
in diameter and 10 mm in thickness) and has almost no capability to measure the absorptance of large-
sized laser components (100 mm in diameter and over) widely used in high-power/high-energy laser
systems. In addition, laser calorimetry has only limited capability to map the absorptance distribution
of an optical laser component.
The measurement procedures in this document have been optimized to allow the mapping of absorbing
defects of optical laser components and measurement of absolute absorptance of large-sized laser optics
actually used in high-power/high-energy laser systems using photothermal techniques which provide
absorption measurement/mapping with high sensitivity, high spatial resolution, and high reliability.
In addition to absorption measurement/mapping of optical laser components with photothermal
amplitude, the photothermal phase measurement/mapping can also find applications in thermo-
physical characterization of laser optics, which will be helpful for a better understanding of defect
properties of laser optics and laser-defect interaction that would lead to a better understanding of
laser-induced damage mechanism of laser optics.
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INTERNATIONAL STANDARD ISO 23701:2023(E)
Optics and photonics — Laser and laser-related equipment
— Photothermal technique for absorption measurement
and mapping of optical laser components
1 Scope
This document specifies procedures for the absorption measurement and high spatial-resolution
two-dimensional or three-dimensional absorption mapping of optical laser components, and upon
calibration, the measurement of absolute absorptance of laser optics.
The methods given in this document are intended to be used for the two-dimensional or three-
dimensional absorption mapping of optical laser components, that is, measurement of absorption as a
function of position, as well as absorption/absorptance measurement and mapping of laser optics used
in high-power/high-energy laser systems.
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 terminol
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