SIST EN ISO 13694:2026

• Abstract:

  This document specifies methods by which the measurement of irradiance (fluence) distribution is made and specifies parameters for the characterization of the spatial properties of laser irradiance (fluence) distribution functions at a given plane.; The methods given in this document are intended to be used for the testing and characterization of both continuous wave (cw) and pulsed laser beams used in optics and optical instruments.; This document provides definitions of terms and symbols to be used in referring to irradiance distribution, as well as requirements for its measurement. For pulsed lasers, the distribution of time-integrated irradiance (i.e. radiant exposure) is the quantity most often measured.

• Status: Published
• Public Enquiry End Date: 29-Jun-2025
• Publication Date: 19-Aug-2026
• ICS: 11.040.70 - Ophthalmic equipment
• ICS: 31.260 - Optoelectronics. Laser equipment
• Technical Committee: VAZ - Healthcare
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 30-Jul-2026
• Due Date: 04-Oct-2026
• Completion Date: 20-Aug-2026
• Ref Project: EN ISO 13694:2026 - Optics and photonics - Lasers and laser-related equipment - Test methods for laser beam irradiance (fluence) distribution (ISO 13694:2026)

• Replaces: SIST EN ISO 13694:2019 - Optics and photonics - Lasers and laser-related equipment - Test methods for laser beam power (energy) density distribution (ISO 13694:2018)
• Effective Date: 01-Sep-2026

Overview

SIST EN ISO 13694:2026 establishes standardized test methods for measuring and characterizing the spatial distribution of laser beam irradiance (for continuous waves) and fluence (for pulsed sources). Developed by the Slovenian Institute for Standardization (SIST) and aligned with ISO and CEN requirements, this standard provides terminology, symbols, and procedural requirements for consistent measurement of laser beam parameters at a specific plane.

Focusing on both continuous wave (cw) and pulsed lasers, SIST EN ISO 13694:2026 applies to diverse optics, photonics, and laser-related equipment, facilitating reliable comparison, evaluation, and qualification of laser beam quality across industrial, scientific, and medical applications.

Key Topics

• Measurement Methods: Provides multiple approaches for quantifying laser beam irradiance (fluence) distributions, including:

  • 1D and 2D camera arrays
  • Aperture-based techniques (pinholes, slits, knife edges)
  • Variable aperture or "power-in-a-bucket" methods

• Defining Parameters: Standardizes parameters for beam characterization such as:

  • Irradiance distribution (E(x, y, z))
  • Fluence distribution for pulsed lasers (H(x, y, z))
  • Beam centroid, widths, diameters, and ellipticity
  • Encircled-power and clip-level beam widths/diameters
  • Uniformity, flatness factor, and edge steepness

• Equipment and Calibration: Details the requirements for detector systems (spatial resolution, dynamic range, calibration), environmental controls, and alignment procedures to ensure accurate, reproducible, and traceable results.

• Definitions and Terminology: Harmonizes vocabulary for laser measurements in line with ISO 11145, ISO 11146-1, and IEC Electropedia, ensuring unambiguous communication.

Applications

SIST EN ISO 13694:2026 is widely relevant wherever accurate laser beam assessment is crucial:

• Optical Manufacturing: Enables quality control when evaluating laser beam spatial profiles, essential for precision optics, lens manufacturing, and laser-based fabrication.
• Laser Alignment and Qualification: Supports alignment, certification, and performance qualification of laser sources in laboratories, medical devices, and industrial settings.
• Safety and Compliance: Provides reliable data needed for regulatory compliance, risk assessments, and adherence to relevant safety and performance standards.
• Research and Development: Facilitates repeatable, comparable results for academic, industrial, and government research activities involving lasers, photonics, or optoelectronics.
• Medical Lasers: Essential for characterizing laser devices used in ophthalmology, dermatology, and surgery where spatial beam properties directly impact clinical outcomes.

Related Standards

Organizations implementing or referencing SIST EN ISO 13694:2026 may also benefit from familiarity with the following standards:

• ISO 11145: Optics and photonics - Laser 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 11554: Optics and photonics - Lasers and laser-related equipment - Test methods for laser beam radiant power, radiant energy, and temporal characteristics
• ISO/TR 11146-3: Further test methods for measuring beam widths and amplitude distributions

Practical Value

By adopting SIST EN ISO 13694:2026, organizations ensure consistency, comparability, and reliability in laser beam characterization. This standard streamlines performance verification, supports global trade and innovation in optics and photonics, and underpins safety, efficiency, and product quality in an expanding array of laser-related applications.

SLOVENSKI STANDARD
01-september-2026
Nadomešča:
SIST EN ISO 13694:2019
Optika in fotonska tehnologija - Laserji in laserska oprema - Metode za
preskušanje porazdelitve obsevanosti (fluence) laserskega žarka (ISO 13694:2026)
Optics and photonics - Lasers and laser-related equipment - Test methods for laser
beam irradiance (fluence) distribution (ISO 13694:2026)
Optik und Photonik - Laser und Laseranlagen - Prüfverfahren für die Leistungs-
(Energie‑)dichteverteilung von Laserstrahlen (ISO 13694:2026)
Optique et photonique - Lasers et équipements associés aux lasers - Méthodes d’essai
de distribution de l’éclairement énergétique (exposition énergétique) du faisceau laser
(ISO 13694:2026)
Ta slovenski standard je istoveten z: EN ISO 13694:2026
ICS:
11.040.70 Oftalmološka oprema Ophthalmic equipment
31.260 Optoelektronika, laserska Optoelectronics. Laser
oprema equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 13694
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2026
EUROPÄISCHE NORM
ICS 31.260 Supersedes EN ISO 13694:2018
English Version
Optics and photonics - Lasers and laser-related equipment
- Test methods for laser beam irradiance (fluence)
distribution (ISO 13694:2026)
Optique et photonique - Lasers et équipements Optik und Photonik - Laser und Laseranlagen -
associés aux lasers - Méthodes d'essai de distribution Prüfverfahren für die Bestrahlungsstärke-(Fluenz-
de l'éclairement énergétique (exposition énergétique) )verteilung von Laserstrahlen (ISO 13694:2026)
du faisceau laser (ISO 13694:2026)
This European Standard was approved by CEN on 12 July 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 13694:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 13694:2026) 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 January 2027, and conflicting national standards shall
be withdrawn at the latest by January 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 13694:2018.
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 13694:2026 has been approved by CEN as EN ISO 13694:2026 without any modification.

International
Standard
ISO 13694
Fourth edition
Optics and photonics — Lasers and
2026-07
laser-related equipment — Test
methods for laser beam irradiance
(fluence) distribution
Optique et photonique — Lasers et équipements associés aux
lasers — Méthodes d’essai de distribution de l’éclairement
énergétique (exposition énergétique) du faisceau laser
Reference number
ISO 13694:2026(en) © ISO 2026
ISO 13694:2026(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 13694:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Measured quantities .1
3.2 Characterizing parameters .3
4 Coordinate system . 9
5 Characterizing parameters derived from the measured spatial distribution . 9
6 Test principle . 9
7 Measurement arrangement and test equipment . 10
7.1 General .10
7.2 Preparation .10
7.3 Control of environment . .10
7.4 Detector system.10
7.5 Beam-forming optics, optical attenuators, and beam splitters .11
8 Test procedure .11
8.1 Equipment preparation . .11
8.2 Detector calibration procedure . 12
8.2.1 Spatial calibration . 12
8.2.2 Radiant power (energy) calibration . 12
8.3 Data recording and noise correction . 12
8.3.1 General . 12
8.3.2 Correction by background-map subtraction . 13
8.3.3 Correction by average background subtraction . 13
9 Evaluation . 14
10 Test report . 14
Annex A (informative) Test report .15
Bibliography .18

iii
ISO 13694:2026(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 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 fourth edition cancels and replaces the third edition (ISO 13694:2018), which has been technically
revised.
The main changes are as follows:
— Terminologies “power”, “energy”, “power density”, and “energy density” were replaced by “radiant power”,
“radiant energy”, “irradiance”, and “fluence”, respectively, in order to be consistent with ISO 80000-7 and
IEC Electropedia (https://www.electropedia.org/).
— The terminologies “beam width” and “beam diameter” were restricted to be used only for those given
by the second order moment which is defined in ISO 11146-1, and new terminologies “encircled-power
beam width”, “encircled-power beam diameter”, “clip-level beam width”, and “clip-level beam diameter”
were introduced, in order to avoid confusion of plural definitions.
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 13694:2026(en)
Introduction
Many applications of lasers involve using the near-field as well as the far-field irradiance (fluence)
distribution of the beam. The irradiance (fluence) distribution of a laser beam is characterized by the spatial
distribution of radiant power density (radiant energy fluence) with lateral displacement in a particular plane
perpendicular to the direction of propagation. In general, the irradiance (fluence) distribution of the beam
changes along the direction of propagation. Depending on the radiant power (energy), size, wavelength,
polarization, and coherence of the beam, different methods of measurement are applicable in different
situations. Five methods are commonly used: camera arrays (1D and 2D), apertures, pinholes, slits, and
knife edges.
According to ISO 11145, it is possible to use two different definitions for describing and measuring the laser
beam diameter. One definition is based on the measurement of the encircled radiant power (energy); the
other is based on determining the spatial moments of the irradiance (fluence) distribution of the laser beam.
The use of spatial moments is necessary for calculating the beam propagation factor, K, and the beam
propagation ratio, M , from measurements of the beam widths at different distances along the propagation
axis. ISO 11146-1 and ISO 11146-2 describe this measurement procedure. For other applications, other
definitions for the beam diameter can be used. For some quantities used in this document the beam width
based on the encircled radiant power (energy) is more appropriate and easier to use.

v
International Standard ISO 13694:2026(en)
Optics and photonics — Lasers and laser-related equipment
— Test methods for laser beam irradiance (fluence)
distribution
1 Scope
This document specifies methods by which the measurement of irradiance (fluence) distribution is made
and specifies parameters for the characterization of the spatial properties of laser irradiance (fluence)
distribution functions at a given plane.
The methods given in this document are intended to be used for the testing and characterization of both
continuous wave (cw) and pulsed laser beams used in optics and optical instruments.
This document provides definitions of terms and symbols to be used in referring to irradiance distribution,
as well as requirements for its measurement. For pulsed lasers, the distribution of time-integrated irradiance
(i.e. radiant exposure) is the quantity most often measured.
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 — Laser 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/TR 11146-3, Lasers and laser-related equipment — Test methods for laser beam widths, divergence angles
and beam propagation ratios — Part 3: Intrinsic and geometrical laser beam classification, propagation and
details of test methods
3 Terms and definitions
For the purposes of 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/
3.1 Measured quantities
3.1.1
irradiance distribution
E(x, y, z)
set of all radiant power densities at location z of a certain cw beam with non-negative values for all transverse
coordinates (x, y)
Note 1 to entry: E(x, y, z) is represented as a density of incident radiant power P(z) with respect to area A at a location
(x, y).
ISO 13694:2026(en)
dPz()
Ex(, yz,)=
dA
[SOURCE: ISO 80000-7:2019, 7-7.1, modified — Radiant flux symbol, Φ , has been replaced by P(z).]
e
3.1.1.1
irradiance
E(x , y , z)
P P
portion of the beam radiant power at location z which impinges on the area, δA, at the location (x , y ) divided
P P
by the area δA in the limit δA → 0
[SOURCE: ISO 11145:2026, 3.13.6, modified — Notes to entry have been omitted.]
3.1.2
fluence distribution
H(x, y, z)
set of all radiant exposure at location z of a certain pulsed beam with non-negative values for all transverse
coordinates (x, y)
Hx(, yz,) Ex(, yz,)dt

3.1.2.1
fluence
H(x , y , z)
P P
portion of the beam radiant energy (time-integrated radiant power) at location z which
impinges on the area, δA, at the location (x , y ) divided by the area δA in the limit δA → 0
P P
Hx(, yz,) Ex(, yz,)dt
PP  PP
[SOURCE: ISO 11145:2026, 3.13.4, modified — Notes to entry have been omitted.]
Note 1 to entry: The terminology “fluence” described in this document is equivalent to “radiant exposure” (refer to
ISO 80000-7).
3.1.3
radiant power
P(z)
rate of radiant energy transfer in a continuous wave (cw) beam at location z
Pz() Ex(, yz,)ddxy

3.1.4
radiant pulse energy
Q(z)
radiant energy in one pulse measured at location z
Qz() Hx(, yz,)ddxy

[SOURCE: ISO 11145:2026, 3.13.3, modified — "Measured at location z", formula Q(z) and “radiant” have
been included in the term.]
3.1.5
maximum irradiance
E (z)
max
maximum of the spatial irradiance distribution (3.1.1) function E(x, y, z) at location z

ISO 13694:2026(en)
3.1.6
maximum fluence
H (z)
max
maximum of the spatial fluence distribution (3.1.2) function H(x, y, z) at location z
3.1.7
location of the maximum
(x , y , z)
max max
location of E (z) or H (z) in the xy plane at location z
max max
Note 1 to entry: (x , y , z) cannot be uniquely defined when measuring with detectors having a high spatial
max max
resolution and a relatively small dynamic range.
3.1.8
clip-level irradiance
E (z)
ηCL
fraction η of the maximum irradiance (3.1.5) at location z
Ez()Ez()
CL max
0 ≤ η < 1
Note 1 to entry: When no confusion is possible, the explicit dependence on z is dropped in the text description using
some quantities, but not in the definitions or in the Formulae involving the quantities.
3.1.9
clip-level fluence
H (z)
ηCL
fraction η of the maximum fluence (3.1.6) at location z
Hz()Hz()
CL max
0 ≤ η < 1
Note 1 to entry: When no confusion is possible, the explicit dependence on z is dropped in the text description using
some quantities, but not in the definitions or in the Formulae involving the quantities.
3.2 Characterizing parameters
3.2.1
clip-level radiant power
P (z)
η
integral of the radiant power (3.1.3) distribution at location z, evaluated by summing only over locations
(x,y) for which E(x, y, z) > E (z)
ηCL
3.2.2
clip-level radiant energy
Q (z)
η
integral of the radiant pulse energy (3.1.4) distribution at location z, evaluated by summing only over
locations (x,y) for which H(x, y, z) > H (z)
ηCL
ISO 13694:2026(en)
3.2.3
fractional radiant power
f (z)
η
fraction of the clip-level radiant power (3.2.1) for a given η to the total radiant power (3.1.3) in the distribution
at location z
Pz()

fz()

Pz()
0 ≤ f (z) ≤ 1
η
3.2.4
fractional radiant energy
g (z)
η
fraction of the clip-level radiant energy (3.2.2) for a given η to the total radiant pulse energy (3.1.4) in the
distribution at location z
Qz()

gz()

Qz()
0 ≤ g (z) ≤ 1
η
3.2.5
beam centroid
xz(),(yz)
 
coordinates of the first-order moments of a radiant power (3.1.3) distribution or a radiant pulse energy (3.1.4)
distribution of a beam at location z
xE(,xy,)zxddy

xz()
Ex(, yz,)ddxy

yE(,xy,)zxddy

yz()
Ex(, yz,)ddxy

where the integration shall be performed over an area such that at least 99 % of the beam radiant power
(3.1.3) or radiant pulse energy (3.1.4) is captured
Note 1 to entry: The irradiance (3.1.1.1) E is replaced by the fluence (3.1.2.1) H for pulsed lasers.
Note 2 to entry: For a more detailed definition, see ISO 11145 and ISO 11146-1.
3.2.6
beam width
d (z), d (z)
σx σy
widths d (z) and d (z) of the beam in the respective x and y directions at z, equal to four times the square
σx σy
2 2
root of the second order moments σ ()z and σ ()z of the irradiance distribution (3.1.1) or fluence
x y
distribution (3.1.2) about the centroid
dz() 4 ()z
xx
dz() 4 ()z
 yy
ISO 13694:2026(en)
 
xzx() Ex(, yz,) ddxy
 
 
 
2  
 ()z 
x
 
Ex(, yz,)ddxy
 
 
 
yy ()zE (,xy,)zxddy
 
 
2  
 ()z 
y
 
Ex(, yz,)ddxy
 
 
Note 1 to entry: Refer to ISO 11145 and ISO 11146-1.
3.2.7
beam diameter
d (z)
σ
diameter defined by using the second order moment σ()z of the irradiance distribution (3.1.1) function or
fluence distribution (3.1.2) function
dz() 22()z

 
xx ()zy  yz() Ex(, yz,)ddxy
   

 
 ()z 
 
Ex(, yz,)ddxy
 
 
3.2.8
encircled-power beam width
d (z), d (z)
x,u y,u
widths d (z) and d (z) of the smallest slit aligned with the principal axis X or Y of the irradiance distribution
x,u y,u
(3.1.1) function or fluence distribution (3.1.2) function, transmitting u % of the total beam radiant power
(3.1.3) or radiant pulse energy (3.1.4) along X or Y
Note 1 to entry: The encircled-power beam widths d (z) and d (z) can be measured by the moving knife-edge
x,u y,u
method (refer to ISO/TR 11146-3).
3.2.9
encircled-power beam diameter
d (z)
u
diameter of the smallest circular aperture in a plane perpendicular to the beam axis that contains u % of the
total beam radiant power (3.1.3) or radiant pulse energy (3.1.4)
Note 1 to entry: For u=86,5, d (z) corresponds to the uncorrected beam diameter measured by the variable aperture
u
method (see ISO/TR 11146-3). The connection factor relating d and d is given in ISO/TR 11146-3.
86,5 σ
3.2.10
clip-level beam width
CL CL
dz(),(dz)
xy,,ηη
CL CL
widths dz() and dz() of the slit area aligned with the principal axis x or y of the irradiance distribution
x,η y,η
(3.1.1) function or fluence distribution (3.1.2) function, wherein irradiance (3.1.1.1) E(x, y, z) > E (z) or
ηCL
fluence (3.1.2.1) H(x, y, z) > H (z)
ηCL
Note 1 to entry: If η=0.5, then the clip-level beam width is so-called FWHM (full width at half maximum).

ISO 13694:2026(en)
CL CL
Note 2 to entry: For ideal Gaussian beam (TEM ), dz()dz() , and dz()dz() .
x  y
2 2
x,/1 e y,/1 e
Note 3 to entry: The position where the clip-level beam width is minimum does not necessarily coincide with the beam
waist position.
3.2.11
clip-level beam diameter
CL
dz()
η
diameter of a circular aperture in a plane perpendicular to the beam axis wherein irradiance (3.1.1.1) E(x, y,
z) > E (z) or fluence (3.1.2.1) H(x, y, z) > H (z)
ηCL ηCL
CL
Note 1 to entry: For ideal Gaussian beam (TEM ), dz()dz() .

1/e
Note 2 to entry: The position where the clip-level beam diameter is minimum does not necessarily coincide with the
beam waist position.
3.2.12
beam ellipticity
ε(z)
parameter for quantifying the circularity or squareness of a radiant power (3.1.3) distribution or a radiant
pulse energy (3.1.4) distribution at an axial location z
 
min(dz),dz()
xy''
 
()z 
 
max(dz),dz()
xy''
 
Note 1 to entry: It follows that 0<ε(z)≤1.
Note 2 to entry: If ε ≥ 0,87, elliptical distributions can be regarded as circular.
Note 3 to entry: In case of a rectangular distribution, beam ellipticity is often referred to as aspect ratio.
Note 4 to entry: In contrast to the definition given here, in literature the term beam ellipticity is sometimes related to
dz()
 y
1 . The definition given here has been chosen to be in concordance with the same definition of beam
dz()
x
ellipticity in ISO 11146-1 and ISO 11145.
[SOURCE: ISO 11146-1:2021, 3.6, modified — In Note 4 to entry ISO 13694 has been ch
...