kSIST FprEN ISO 13694:2026

Optics and photonics - Lasers and laser-related equipment - Test methods for laser beam irradiance (fluence) distribution (ISO/FDIS 13694:2026)

This document specifies methods by which the measurement of power (energy) density distribution is made and defines parameters for the characterization of the spatial properties of laser power (energy)density 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 power density distribution, as well as requirements for its measurement. For pulsed lasers, the distribution of time-integrated power density (i.e. energy density) is the quantity most often measured.

Optik und Photonik - Laser und Laseranlagen - Prüfverfahren für die Leistungs-(Energie‑)dichteverteilung von Laserstrahlen (ISO/FDIS 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/FDIS 13694:2026)

Le présent document spécifie des méthodes permettant de procéder au mesurage de la distribution de densité de puissance (d'énergie) et définit les paramètres de caractérisation des propriétés spatiales des fonctions de distribution de densité de puissance (d'énergie) laser dans un plan donné.
Les méthodes d'essai données dans le présent document sont destinées à être utilisées dans le cadre des essais et de la caractérisation des faisceaux laser continus et impulsionnels.
Le présent document donne des définitions de la terminologie et des symboles à utiliser dans le cadre de la distribution de la densité de puissance, ainsi que les spécifications relatives au mesurage de cette distribution. Pour les lasers impulsionnels, la distribution de la densité de puissance intégrée sur le temps (c'est-à-dire la densité d'énergie) représente la grandeur la plus souvent mesurée.

Optika in fotonska tehnologija - Laserji in laserska oprema - Metode za preskušanje porazdelitve obsevanosti (fluence) laserskega žarka (ISO/FDIS 13694:2026)

General Information

• Status: Not Published
• Public Enquiry End Date: 29-Jun-2025
• ICS: 11.040.70 - Ophthalmic equipment
• ICS: 31.260 - Optoelectronics. Laser equipment
• Technical Committee: VAZ - Healthcare
• Current Stage: 5020 - Formal vote (FV) (Adopted Project)
• Start Date: 24-Apr-2026
• Due Date: 12-Jun-2026
• Ref Project: FprEN ISO 13694 - Optics and photonics - Lasers and laser-related equipment - Test methods for laser beam irradiance (fluence) distribution (ISO/FDIS 13694:2026)

Relations

• Revises: 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: 25-Sep-2024

Overview

kSIST FprEN ISO 13694:2026 establishes standardized test methods for measuring and characterizing the spatial distribution of laser beam irradiance (fluence) in optics and photonics applications. Developed by CEN and based on ISO/FDIS 13694:2026, this standard ensures consistency in the measurement of power and energy density profiles for both continuous wave (cw) and pulsed lasers. It provides critical definitions, measurement parameters, and requirements for accurately assessing the spatial properties of laser beams at a specified test plane.

By facilitating reliable measurement protocols, kSIST FprEN ISO 13694:2026 supports manufacturers, laboratories, and users in evaluating laser and laser-related equipment, promoting product quality, safety, and interoperability within the optoelectronics field.

Key Topics

• Irradiance (Fluence) Distribution: Standardizes terminology and methods for assessing spatial distribution of radiant power (cw) and radiant energy (pulsed lasers), including detailed guidelines for integration and background subtraction.

• Characterization Parameters: Defines important spatial properties such as:

  • Beam centroid and diameter (using second order moments)
  • Encircled-power and clip-level widths/diameters
  • Beam ellipticity and cross-sectional area
  • Average irradiance/fluence, flatness, and uniformity
  • Edge steepness and plateau uniformity

• Measurement Methods: Outlines best practices for:

  • Detector system requirements (high spatial resolution, high dynamic range, specific calibration needs)
  • Use of camera arrays, pinholes, slits, knife edges, and apertures for spatial mapping
  • Environmental control to minimize noise and errors
  • Test setup alignment and optical component considerations

• Data Evaluation: Prescribes calculation of measurement parameters and correct reporting formats, ensuring traceability and reproducibility across the optics and photonics industry.

Applications

kSIST FprEN ISO 13694:2026 is pivotal for professionals involved in:

• Optical Instrument Development: Ensures precise characterization of laser beams used in microscopy, spectroscopy, metrology, and other scientific instruments requiring defined beam uniformity and profile.
• Laser Manufacturing & Quality Control: Provides methods for QC testing during production of lasers and related devices, facilitating international compatibility and product safety.
• Medical and Ophthalmic Equipment: Supports the testing of laser sources in medical devices (e.g., surgical lasers, ophthalmic lasers) where the distribution of laser energy is critical for performance and patient safety.
• Industrial Laser Systems: Applies to material processing lasers (cutting, welding, marking) where beam profile influences process efficiency and end-product quality.
• Research and Metrology Laboratories: Enables accurate standardization of laser measurements, supporting both R&D and international comparison of results.

Related Standards

For comprehensive compliance and deeper integration, reference these associated standards:

• ISO 11145: Vocabulary and symbols for optics and photonics - essential for terminology alignment.
• ISO 11146-1: Test methods for laser beam widths, divergence, and propagation ratios of stigmatic and astigmatic beams.
• ISO 11554: Methods for measuring laser beam radiant power, energy, and temporal characteristics.
• ISO/TR 11146-3: Supplementary methods, including variable aperture and scanning techniques for beam width measurements.
• IEC Electropedia: For consistency in electrotechnical terminology related to lasers and optoelectronics.

Practical Value

Adopting kSIST FprEN ISO 13694:2026 empowers organizations to achieve:

• Consistent Laser Performance Characterization: Ensures data compatibility and reliable communication of laser specifications across suppliers and users.
• Regulatory Compliance: Satisfies requirements for product certification and safety regulations in optical and photonic industries.
• Market Access: Facilitates entry into global markets by aligning with internationally recognized test methods.
• Improved Product Safety and Quality: Reduces risks associated with beam profile inconsistencies-crucial in sensitive applications like medicine or high-precision manufacturing.

By following the standardized approaches outlined in kSIST FprEN ISO 13694:2026, professionals in optics, photonics, and related technology fields benefit from heightened accuracy, improved interoperability, and enhanced confidence in laser performance evaluation.

Standards Content (Sample)

SLOVENSKI STANDARD
oSIST prEN ISO 13694:2025
01-junij-2025
Optika in fotonska tehnologija - Laserji in laserska oprema - Metode za
preskušanje porazdelitve obsevanosti (fluence) laserskega žarka (ISO/DIS
13694:2025)
Optics and photonics - Lasers and laser-related equipment - Test methods for laser
beam irradiance (fluence) distribution (ISO/DIS 13694:2025)
Optik und Photonik - Laser und Laseranlagen - Prüfverfahren für die Leistungs-
(Energie‑)dichteverteilung von Laserstrahlen (ISO/DIS 13694:2025)
Optique et photonique - Lasers et équipements associés aux lasers - Méthodes d’essai
de distribution de l’éclairement énergétique (exposition énergétique) du faisceau laser
(ISO/DIS 13694:2025)
Ta slovenski standard je istoveten z: prEN ISO 13694 rev
ICS:
11.040.70 Oftalmološka oprema Ophthalmic equipment
31.260 Optoelektronika, laserska Optoelectronics. Laser
oprema equipment
oSIST prEN ISO 13694:2025 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN ISO 13694:2025
oSIST prEN ISO 13694:2025
DRAFT
International
Standard
ISO/DIS 13694
ISO/TC 172/SC 9
Optics and photonics — Lasers and
Secretariat: DIN
laser-related equipment — Test
Voting begins on:
methods for laser beam irradiance
2025-04-17
(fluence) distribution
Voting terminates on:
2025-07-10
Optique et photonique — Lasers et équipements associés aux
lasers - Méthodes d'essai de distribution d'irradiance (fluence) du
faisceau laser
ICS: 31.260
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS.
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 13694:2025(en)
oSIST prEN ISO 13694:2025
DRAFT
ISO/DIS 13694:2025(en)
International
Standard
ISO/DIS 13694
ISO/TC 172/SC 9
Optics and photonics — Lasers and
Secretariat: DIN
laser-related equipment — Test
Voting begins on:
methods for laser beam irradiance
(fluence) distribution
Voting terminates on:
Optique et photonique — Lasers et équipements associés aux
lasers - Méthodes d'essai de distribution d'irradiance (fluence) du
faisceau laser
ICS: 31.260
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
BE CONSIDERED IN THE LIGHT OF THEIR
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
or ISO’s member body in the country of the requester.
NATIONAL REGULATIONS.
ISO copyright office
RECIPIENTS OF THIS DRAFT ARE INVITED
CP 401 • Ch. de Blandonnet 8
TO SUBMIT, WITH THEIR COMMENTS,
CH-1214 Vernier, Geneva
NOTIFICATION OF ANY RELEVANT PATENT
Phone: [phone]
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 13694:2025(en)
ii
oSIST prEN ISO 13694:2025
ISO/DIS 13694:2025(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 . 8
5 Characterizing parameters derived from the measured spatial distribution . 8
6 Test principle . 9
7 Measurement arrangement and test equipment . 9
7.1 General .9
7.2 Preparation .9
7.3 Control of environment . .9
7.4 Detector system.9
7.5 Beam-forming optics, optical attenuators, and beam splitters .10
8 Test procedure .10
8.1 Equipment preparation . .10
8.2 Detector calibration procedure .11
8.2.1 Spatial calibration .11
8.2.2 Radiant power (energy) calibration .11
8.3 Data recording and noise correction .11
8.3.1 General .11
8.3.2 Correction by background-map subtraction . 12
8.3.3 Correction by average background subtraction . 12
9 Evaluation .13
10 Test report .13
Annex A (informative) Test report . 14
Bibliography . 17

iii
oSIST prEN ISO 13694:2025
ISO/DIS 13694:2025(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of any patent
rights identified during the development of the document will be in the Introduction and/or on the ISO list of
patent declarations received (see www.iso.org/patents).
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.
This fourth edition cancels and replaces the third edition (ISO 13694:2018), which has been technically
revised. The main changes compared to the previous edition are as follows:
a) 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 8000-7 and IEC Electropedia (https://www.electropedia.org/).
b) 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
oSIST prEN ISO 13694:2025
ISO/DIS 13694:2025(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 describes 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
oSIST prEN ISO 13694:2025
oSIST prEN ISO 13694:2025
DRAFT International Standard ISO/DIS 13694:2025(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 defines 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 11554, Optics and photonics — Lasers and laser-related equipment — Test methods for laser beam radiant
power, radiant energy and temporal characteristics
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 terminological 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).

oSIST prEN ISO 13694:2025
ISO/DIS 13694:2025(en)
dPz()
Ex(,yz,)=
dA
[SOURCE: ISO 80000-7, 7-7.1, modified]
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/DIS 11145:2025, 3.13.6, modified — Notes to entry 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/DIS 11145:2025, 3.13.4, modified — Notes to entry 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/DIS 11145:2025, 3.13.3 modified — Included "Measured at location z", formula Q(z) and
“radiant” in the term.]
3.1.5
maximum irradiance (fluence)
E (z) [H (z)]
max max
maximum of the spatial irradiance (fluence) distribution function E (x, y, z) (H (x, y, z)] at location z

oSIST prEN ISO 13694:2025
ISO/DIS 13694:2025(en)
3.1.6
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.
3.1.7
clip-level irradiance (fluence)
E (z) [H (z)]
ηCL ηCL
fraction η of the maximum irradiance (fluence) (3.1.5) at location z
Ez()=ηEz()
ηCL max
Hz()=ηHz()
ηCL 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 (energy)
P (z) [Q (z)]
η η
integral of the radiant power (energy) distribution at location z, evaluated by summing only over locations
(x,y) for which E (x, y, z) > E (z) (H (x, y, z) > H (z))
ηCL ηCL
3.2.2
fractional radiant power (energy)
f (z)
η
fraction of the clip-level radiant power (energy) (3.2.1) for a given η to the total radiant power (energy) in the
distribution at location z
Pz()
η
fz()= for cw-beams
η
Pz()
Qz()
η
fz()= for pulsed beams
η
Qz()
0 ≤ f (z) ≤ 1
η
3.2.3
beam centroid
((xz), yz())
coordinates of the first-order moments of a radiant power(energy) distribution of a beam at location z
xE⋅⋅(,xy,)zxddy
∫∫
xz()=
Ex(, yz,)⋅ddxy
∫∫
yE⋅⋅(,xy,)zxddy
∫∫
yz()=
Ex(, yz,)⋅ddxy
∫∫
oSIST prEN ISO 13694:2025
ISO/DIS 13694:2025(en)
where the integration shall be performed over an area such that at least 99 % of the beam radiant power
(energy) is captured
Note 1 to entry: The irradiance E is replaced by the fluence H for pulsed lasers.
Note 2 to entry: For a more detailed definition, see ISO 11145 and ISO 11146-1.
3.2.4
beam widths
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 (fluence) distribution about the
x y
centroid
dz()=4σ ()z
σxx
dz()=4σ ()z
σ yy
∞ ∞
xx− ()zE ⋅⋅(,xy,)zxddy
∫ ∫  
−∞−∞
σ ()z =
x
∞ ∞
Ex(, yz,)⋅ddxy
∫ ∫
−∞∞−∞
∞ ∞
yy− ()zE ⋅⋅(,xy,)zxddy
∫ ∫  
−∞−∞
σ ()z =
y
∞ ∞
Ex(, yz,)⋅ddxy
∫ ∫
−∞∞−∞
Note 1 to entry: Refer to ISO 11145 and ISO 11146-1.
3.2.5
beam diameter
d (z)
σ
diameter defined by using the second order moment σ()z of the irradiance (fluence) distribution function
dz()=22σ()z
σ
∞ ∞
 
((xx−+zy)) ((− yz)) Ex(, yz,)dxdy
∫∫
 
2 −−∞ ∞
σ ()z =
∞ ∞
E((,xy,)zdxdy
∫∫
−−∞ ∞
3.2.6
encircled-power beam widths
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 (fluence)
x,u y,u
distribution function, transmitting u % of the total beam power (energy) 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).

oSIST prEN ISO 13694:2025
ISO/DIS 13694:2025(en)
3.2.7
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 (energy)
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
3.2.8
clip-level beam widths
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 (fluence)
x,η y,η
distribution function, wherein irradiance E(x, y, z) > E (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).
CL CL
Note 2 to entry: For ideal Gaussian beam (TEM ), dz()=dz() , and dz()=dz() .
σx σ y
2 2
xe,/1 ye,/1
Note 3 to entry: The position where the clip-level width is minimum does not necessarily coincide with the beam waist
position.
3.2.9
clip-level beam diameter
CL
dz()
η
diameter of a circular aperture in a plane perpendicular to the beam axis wherein irradiance E(x, y, z) > E (z)
ηCL
CL
Note 1 to entry: For ideal Gaussian beam (TEM ), dz()=dz() .
00 σ
1/e
Note 2 to entry: The position where the clip-level diameter is minimum does not necessarily coincide with the beam
waist position.
3.2.10
beam ellipticity
ε (z)
parameter for quantifying the circularity or squareness of a radiant power (energy) distribution at an axial
location z
min(dz),dz()
σσxy''
 
ε()z =
max(dz),dz()
σσxy''
 
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, ellipticity is often referred to as aspect ratio.
Note 4 to entry: In contrast to the definition given here, in literature the term ellipticity is sometimes related to
dz()
σ y
1− . The definition given here has been chosen to be in concordance with the same definition of ellipticity in
dz()
σx
ISO 11146-1 and ISO 11145.
[SOURCE: ISO 11146-1:2021, 3.6 modified: In Note 4 to entry change ISO 13694 to ISO 11145.]

oSIST prEN ISO 13694:2025
ISO/DIS 13694:2025(en)
3.2.11
beam cross-sectional area
A (z)
σ
area of a beam with circular cross-section
π
  2
Ad= ⋅ ()z
 
σσ
 4 
or elliptical cross-section
π
 
Ad= ⋅⋅()zd ()z
 
σσxyσ
 
Note 1 to entry: For clarity, the term “beam cross-sectional area” is always used in combination with the symbol and
its appropriate subscript: A or A .
u σ
[SOURCE: ISO/DIS 11145:2025, 3.6.2]
3.2.12
clip-level irradiation area
i
Az()
η
irradiation area at location z for which the irradiance (fluence) exceeds the clip-level irradiance (fluence) (3.1.7)
Note 1 to entry: To allow for distributions of all forms, for example hollow “donut” types, the clip-level irradiation area
is not defined in terms of the beam widths (3.2.4) d or d .
σx σy
Note 2 to entry: See clip-level irradiance (fluence) (3.1.7).
3.2.13
clip-level average irradiance (fluence)
E (z), [H (z)]
ηave ηave
spatially averaged irradiance (fluence) of the distribution at location z, defined as the weighted mean
Pz()
η
Ez()= for cw-beams
ηave
i
Az()
η
Qz()
η
Hz()= for pulsed beams
ηave
i
Az()
η
Note 1 to entry: E (z) and E (z) (see 3.1.7) refer
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