SIST EN ISO 11145:2016

SLOVENSKI STANDARD
SIST EN ISO 11145:2016
01-junij-2016
1DGRPHãþD
SIST EN ISO 11145:2008
Optika in fotonska tehnologija - Laserji in z laserji povezana oprema - Slovar in
simboli (ISO 11145:2016)
Optics and photonics - Lasers and laser-related equipment - Vocabulary and symbols
(ISO 11145:2016)
Optik und Photonik - Laser und Laseranlagen - Begriffe und Formelzeichen (ISO
11145:2016)
Optique et photonique - Lasers et équipements associés aux lasers - Vocabulaire et
symboles (ISO 11145:2016)
Ta slovenski standard je istoveten z: EN ISO 11145:2016
ICS:
01.040.31 Elektronika (Slovarji) Electronics (Vocabularies)
01.080.40 *UDILþQLVLPEROL]DXSRUDERY Graphical symbols for use on
ULVEDKGLDJUDPLKQDþUWLKY electrical and electronics
HOHNWURWHKQLNLLQHOHNWURQLNL engineering drawings,
WHUYXVWUH]QLWHKQLþQL diagrams, charts and in
SURL]YRGQLGRNXPHQWDFLML relevant technical product
documentation
31.260 Optoelektronika, laserska Optoelectronics. Laser
oprema equipment
SIST EN ISO 11145:2016 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 11145:2016

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SIST EN ISO 11145:2016


EN ISO 11145
EUROPEAN STANDARD

NORME EUROPÉENNE

March 2016
EUROPÄISCHE NORM
ICS 01.080.40; 01.040.31; 31.260 Supersedes EN ISO 11145:2008
English Version

Optics and photonics - Lasers and laser-related equipment
- Vocabulary and symbols (ISO 11145:2016)
Optique et photonique - Lasers et équipements Optik und Photonik - Laser und Laseranlagen - Begriffe
associés aux lasers - Vocabulaire et symboles (ISO und Formelzeichen (ISO 11145:2016)
11145:2016)
This European Standard was approved by CEN on 19 September 2015.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.





EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2016 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 11145:2016 E
worldwide for CEN national Members.

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SIST EN ISO 11145:2016
EN ISO 11145:2016 (E)
Contents Page
European foreword . 3
Annex ZA (informative) Relationship between this European Standard and the Essential
Requirements of EU Directive 2006/42/EC on machinery . 4

2

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SIST EN ISO 11145:2016
EN ISO 11145:2016 (E)
European foreword
This document (EN ISO 11145:2016) 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 September 2016, and conflicting national standards
shall be withdrawn at the latest by September 2016.
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 11145:2008.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association, and supports essential requirements of EU Directive(s).
For relationship with EU Directive, see informative Annex ZA, which is an integral part of this
document.
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, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 11145:2016 has been approved by CEN as EN ISO 11145:2016 without any modification.
3

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SIST EN ISO 11145:2016
EN ISO 11145:2016 (E)
Annex ZA
(informative)
Relationship between this European Standard and the Essential
Requirements of EU Directive 2006/42/EC on machinery
This European Standard has been prepared under a mandate given to CEN by the European
Commission and the European Free Trade Association to provide a means of conforming to Essential
Requirements of the New Approach Directive 2006/42/EC on machinery.
Once this standard is cited in the Official Journal of the European Union under that Directive and has
been implemented as a national standard in at least one Member State, compliance with the clauses of
this standard given in Table ZA.1 confers, within the limits of the scope of this standard, a presumption
of conformity with the corresponding Essential Requirements of that Directive and associated EFTA
regulations.
Table ZA.1 — Correspondence between this European Standard and EU Directive 2006/42/EC on
machinery
Clauses and subclauses Essential Requirements (ERs)
Qualifying remarks/Notes
of this European standard of EU Directive 2006/42/EC

3 1.5.10
3 1.5.12


WARNING — Other requirements and other EU Directives may be applicable to the product(s) falling
within the scope of this standard.
4

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SIST EN ISO 11145:2016
INTERNATIONAL ISO
STANDARD 11145
Fourth edition
2016-03-01
Optics and photonics — Lasers
and laser-related equipment —
Vocabulary and symbols
Optique et photonique — Lasers et équipements associés aux lasers
— Vocabulaire et symboles
Reference number
ISO 11145:2016(E)
©
ISO 2016

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SIST EN ISO 11145:2016
ISO 11145:2016(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2016 – All rights reserved

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SIST EN ISO 11145:2016
ISO 11145:2016(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Symbols and units of measurement . 1
3 Terms and definitions . 2
3.1 Beam axis . 3
3.2 Beam cross-sectional area . 3
3.3 Beam diameter . 3
3.4 Beam radius . 4
3.5 Beam widths. 5
3.11 Beam waist diameters . 7
3.12 Beam waist radius . 7
3.13 Beam waist widths . . 7
3.14 Beam waist separation . 8
3.19 Divergence angles . 9
Annex A (informative) Explanation of the difference in terminology between IEC 60825-1
and ISO 11145 .15
Annex B (informative) List of symbols .16
Annex C (informative) Alphabetical index .17
Bibliography .19
© ISO 2016 – All rights reserved iii

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SIST EN ISO 11145:2016
ISO 11145:2016(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.
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 on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 172, Optics and photonics, Subcommittee SC 9,
Electro-optical systems.
This fourth edition cancels and replaces the third edition (ISO 11145:2006) which has been technically
revised with the following changes:
a) in 3.5.3, a formula for beam ellipticity has been added;
b) in 3.53, the definition of relative intensity noise has been revised and a formula was added.
iv © ISO 2016 – All rights reserved

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SIST EN ISO 11145:2016
INTERNATIONAL STANDARD ISO 11145:2016(E)
Optics and photonics — Lasers and laser-related
equipment — Vocabulary and symbols
1 Scope
This International Standard defines basic terms, symbols, and units of measurement for the field of
laser technology in order to unify the terminology and to arrive at clear definitions and reproducible
tests of beam parameters and laser-oriented product properties.
NOTE The laser hierarchical vocabulary laid down in this International Standard differs from that given
in IEC 60825–1. ISO and IEC have discussed this difference and agree that it reflects the different purposes for
which the two standards serve. For more details, see informative Annex A.
2 Symbols and units of measurement
2.1 The spatial distribution of power (energy) density of a laser beam does not always have circular
symmetry. Therefore, all terms related to these distributions are split into those for beams with circular
and those with non-circular cross-sections. A circular beam is characterized by its radius, w, or diameter,
d. For a non-circular beam, the beam widths, d and d , for two orthogonal directions have to be given.
x y
2.2 The spatial distributions of laser beams do not have sharp edges. Therefore, it is necessary to
define the power (energy) values to which the spatial terms refer. Depending on the application, different
2
cut-off values can be chosen (for example 1/e, 1/e , 1/10 of peak value).
To clarify this situation, this International Standard uses the subscript u for all related terms to denote
the percentage of the total beam power (energy) taken into account for a given parameter.
NOTE For the same power (energy) content, beam width d and beam diameter d (= 2w ) can differ for the
x,u u u
same value of u (for example, for a circularly symmetric Gaussian beam d is equal to d ).
86,5 x,95,4
Table 1 lists symbols and units which are defined in detail in Clause 3.
Table 1 — Symbols and units of measurement
Symbol Unit Term
2
A or A m Beam cross-sectional area
u σ
d or d m Beam diameter
u σ
d or d m Beam width in x-direction
x,u σx
d or d m Beam width in y-direction
y,u σy
d or d m Beam waist diameter
0,u σ0
d ·Θ /4 rad m Beam parameter product
σ0 σ
2
E or E W/m Average power density
u σ
f Hz Pulse repetition rate
p
2
H or H J/m Average energy density
u σ
K 1 Beam propagation factor
l m Coherence length
c
2
M 1 Beam propagation ratio
p 1 Degree of linear polarization
P W Cw-power
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SIST EN ISO 11145:2016
ISO 11145:2016(E)

Table 1 (continued)
Symbol Unit Term
P W Average power
av
P W Pulse power
H
P W Peak power
pk
Q J Pulse energy
−1
R( f ) Hz or dB/Hz Relative intensity noise, RIN
w or w m Beam radius
u σ
w or w m Beam waist radius
0,u σ0
z m Rayleigh length
R
Δϑ m Misalignment angle
Δλ m Spectral bandwidth in terms of wavelength
Spectral bandwidth in terms of optical
Δν Hz
frequency
Δ (z′) m Beam positional stability in x-direction
x
Δ (z′) m Beam positional stability in y-direction
y
Δz m Astigmatic waist separation
a
Δz 1 Relative astigmatic waist separation
r
ε 1 Ellipticity of a power density distribution
η 1 Laser efficiency
L
η 1 Quantum efficiency
Q
η 1 Device efficiency
T
Θ or Θ rad Divergence angle
u σ
Θ or Θ rad Divergence angle for x-direction
x,u σx
Θ or Θ rad Divergence angle for y-direction
y,u σy
λ m Wavelength
τ s Pulse duration
H
τ s 10 %-pulse duration
10
τ s Coherence time
c
−1
NOTE R( f ) expressed in dB/Hz equals 10 log R( f ) with R( f ) given in Hz .
10
When stating quantities marked by an index “u”, “u” shall always be replaced by the concrete number,
e.g. A for u = 90 %.
90
In contrast to these quantities defined by setting a cut-off value [“encircled power (energy)”], the beam
widths and derived beam properties can also be defined based on the second moment of the power
(energy) density distribution function (see 3.5.2). Only beam propagation ratios based on beam widths
and divergence angles derived from the second moments of the power (energy) density distribution
function allow calculation of the beam propagation. Quantities based on the second moment are marked
by a subscript “σ”.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2 © ISO 2016 – All rights reserved

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SIST EN ISO 11145:2016
ISO 11145:2016(E)

3.1 Beam axis
3.1.1
beam axis
straight line connecting the centroids defined by the first spatial moment of the cross-sectional
profile of power (energy) at successive positions in the direction of propagation of the beam in a
homogeneous medium
3.1.2
misalignment angle
Δϑ
deviation of the beam axis from the mechanical axis defined by the manufacturer
3.2 Beam cross-sectional area
3.2.1
beam cross-sectional area
A
u
〈encircled power (energy)〉 smallest completely filled area containing u % of the total beam power
(energy)
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
3.2.2
beam cross-sectional area
A
σ
〈second moment of power (energy) density distribution function〉 area of a beam with circular
cross-section
2
π× d /4
σ
or elliptical cross-section
π ⋅⋅dd / 4
()
σσxy
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
3.3 Beam diameter
3.3.1
beam diameter
d
u
〈encircled power (energy)〉 smallest diameter of a circular aperture in a plane perpendicular to the
beam axis that contains u % of the total beam power (energy)
Note 1 to entry: For clarity, the term “beam diameter” is always used in combination with the symbol and its
appropriate subscript: d or d .
u σ
3.3.2
beam diameter
d
σ
〈second moment of power (energy) density distribution function〉 smallest diameter of a circular
aperture in a plane perpendicular to the beam axis, defined as
dz = 22σ z
() ()
σ
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SIST EN ISO 11145:2016
ISO 11145:2016(E)

where the second moment of the power density distribution function E(x,y,z) of the beam at the location
z is given by
2
rE⋅⋅(,rzϕϕ,) rrdd
∫∫
2
σ z =
()
Er(,ϕϕ,)zr⋅ ddr
∫∫
where
r
is the distance to the centroid xy,
()
φ is the azimuth angle
and where the first moments give the coordinates of the centroid, i.e.
xE⋅ (,xy,)zxddy
∫∫
x =
Ex(, yz,)ddxy
∫∫
yE⋅ (,xy,)zxddy
∫∫
y =
Ex(, yz,)ddxy
∫∫
Note 1 to entry: In principle, integration has to be carried out over the whole xy plane. In practice, the integration
has to be performed over an area such that at least 99 % of the beam power (energy) is captured.
Note 2 to entry: The power density E has to be replaced by the energy density H for pulsed lasers.
Note 3 to entry: For clarity, the term “beam diameter” is always used in combination with the symbol and its
appropriate subscript: d or d
u σ.
3.4 Beam radius
3.4.1
beam radius
w
u
〈encircled power (energy)〉 smallest radius of an aperture in a plane perpendicular to the beam axis
which contains u % of the total beam power (energy)
Note 1 to entry: For clarity, the term “beam radius” is always used in combination with the symbol and its
appropriate subscript: w or w .
u σ
3.4.2
beam radius
w
σ
〈second moment of power (energy) density distribution function〉 smallest radius of an aperture in a
plane perpendicular to the beam axis, defined as
wz = 2σ z
() ()
σ
2
Note 1 to entry: For a definition of the second moment σ (z), see 3.3.2.
Note 2 to entry: For clarity, the term “beam radius” is always used in combination with the symbol and its
appropriate subscript: w or w .
u σ
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SIST EN ISO 11145:2016
ISO 11145:2016(E)

3.5 Beam widths
3.5.1
beam widths
d , d
x,u y,u
〈encircled power (energy)〉 width of the smallest slit transmitting u % of the total beam power (energy)
in two preferential orthogonal directions x and y which are perpendicular to the beam axis
Note 1 to entry: The preferential directions are given by the smallest beam width and the orthogonal direction.
Note 2 to entry: For circular Gaussian beams, d equals d .
x,95,4 86,5
Note 3 to entry: For clarity, the term “beam widths” is always used in combination with the symbol and its
appropriate subscripts: d , d or d , d .
σx σy x,u y,u
3.5.2
beam widths
d , d
σx σy
〈second moment of power (energy) density distribution function〉 width of the smallest slit in two
preferential orthogonal directions x and y which are perpendicular to the beam axis, defined as
dz = 4σ z
() ()
σxx
dz = 4σ z
() ()
σ yy
where the second moments of the power density distribution function E(x, y, z) of the beam at the
location z are given by
2
()xx−⋅Ex(,, yz)ddxy
∫∫
2
σ z =
()
x
Ex(, yz,)ddxy
∫∫
2
()yy−⋅Ex(, yz,)ddxy
∫∫
2
σ z =
()
y
Ex(, yz,)ddxy
∫∫
where xx− and yy− are the distances to the centroid xy, and where the first moments give
() () ()
the coordinates of the centroid, i.e
xE⋅ (,xy,)zxddy
∫∫
x =
Ex(, yz,)ddxy
∫∫
yE⋅ (,xy,)zxddy
∫∫
y =
Ex(, yz,)ddxy
∫∫
Note 1 to entry: In principle, integration has to be carried out over the whole xy plane. In practice, the integration
has to be performed over an area such that at least 99 % of the beam power (energy) are captured.
Note 2 to entry: The power density E has to be replaced by the energy density H for pulsed lasers.
Note 3 to entry: For clarity, the term “beam widths” is always used in combination with the symbol and its
appropriate subscripts: d , d or d , d .
σx σy x,u y,u
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SIST EN ISO 11145:2016
ISO 11145:2016(E)

3.5.3
beam ellipticity
ε()z
parameter for quantifying the circularity or squareness of a power [energy] density distribution at z
dz()
σ y
ε()z =
dz()
σx
Note 1 to entry: The direction of x is chosen to be along the major axis of the distribution so dd³ .
σσxy
Note 2 to entry: If ε³08, 7 , elliptical distributions can be regarded as circular. In case of a rectangular beam
profile, ellipticity is often referred to as aspect ratio.
3.5.4
circular power density distribution
power density distribution having an ellipticity greater than 0,87
[SOURCE: ISO 11146-1:2005, 3.7]
3.6
beam parameter product
product of the beam waist diameter and the divergence angle divided by 4
d ×Θ /4
σσ0
Note 1 to entry: Beam parameter products for elliptical beams can be given separately for the principal axes of
the power (energy) distribution.
3.7
beam propagation ratio
2
M
DEPRECATED: beam propagation factor
K
measure of how close the beam parameter product is to the diffraction limit of a perfect Gaussian beam
d Θ
1 π
2
σσ0
M == ×
K λ 4
Note 1 to entry: This is equal to the ratio of the beam parameter products for the actual modes of the laser and
the fundamental Gaussian mode (TEM ).
00
Note 2 to entry: The beam propagation ratio is unity for a theoretically perfect Gaussian beam, and has a value
greater than one for any real beam.
2
Note 3 to entry: It is preferable to use M because K is the symbol for the deprecated term and future editions will
no longer use the term “beam propagation factor”.
3.8
beam position
displacement of the beam axis relative to the fixed mechanical axis of an optical system at a specified
plane perpendicular to the mechanical axis of the optical system
Note 1 to entry: The mechanical axis is given by the straight line joining the centroids of the limiting apertures.
6 © ISO 2016 – All rights reserved

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SIST EN ISO 11145:2016
ISO 11145:2016(E)

3.9
beam positional stability
Δ (z’), Δ (z’)
x y
four times the standard deviation of the measured beam positional movement at plane z′
[SOURCE: ISO 11670:2003, 3.6]
Note 1 to entry: These quantities are defined in the beam axis system x,y,z.
3.10
beam waist
portion of a beam where the beam diameter or beam width takes local minimum
3.11 Beam waist diameters
3.11.1
beam waist diameter
d
0,u
〈encircled power (energy)〉 diameter d of the beam at the location of the beam waist
u
Note 1 to entry: For clarity, the term “beam waist diameter” is always used in combination with the symbol and
its appropriate subscripts: d or d .
0,u σ0
3.11.2
beam waist diameter
d
σ0
〈second moment of power (energy) density distribution function〉 diameter d of the beam at the
σ
location of the beam waist
Note 1 to entry: For clarity, the term “beam waist diameter” is always used in combination with the symbol and
its appropriate subscripts: d or d .
0,u σ0
3.12 Beam waist radius
3.12.1
beam waist radius
w
0,u
〈encircled power (energy)〉 radius w of the beam at the location of the beam waist
u
Note 1 to entry: For clarity, the term “beam waist radius” is always used in combination with the symbol and its
appropriate subscripts: w or w .
0,u σ0
3.12.2
beam waist radius
w
σ0
〈second moment of power (energy) density distribution function〉 radius w of the beam at the location
σ
of the beam waist
Note 1 to entry: For clarity, the term “beam waist radius” is always used in combination with the symbol and its
appropriate subscripts: w or w .
0,u σ0
3.13 Beam waist widths
3.13.1
beam waist widths
d , d
x0,u y0,u
〈encircled power (energy)〉 beam widths d and d at the locations of the beam waists in both the x
x,u y,u
and y directions
Note 1 to entry: For clarity, the term “beam waist widths” is always used in combination with the symbol and its
appropriate subscripts: d , d or d , d .
x0,u y0,u σx0 σy0
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SIST EN ISO 11145:2016
ISO 11145:2016(E)

3.13.2
beam waist widths
d , d
σx0 σy0
〈second moment of power (energy) density distribution function〉 beam widths d and d at the
σx σy
locations of the beam waists in both the x and y directions
Note 1 to entry: For clarity, the term “beam waist widths” is always used in combination with the symbol and its
appropriate subscripts: d , d or d , d .
x0,u y0,u σx0 σy0
3.14 Beam waist separation
3.14.1
astigmatic waist separation
Δz
a
axial distance between the beam waist locations in the orthogonal principal planes of a beam possessing
simple astigmatism
[SOURCE: ISO 15367-1:2003, 3.3.4]
Note 1 to entry: Astigmatic waist separation is also known as astigmatic difference.
3.14.2
relative astigmatic waist separation
Δz
r
astigmatic waist separation divided by the arithmetic mean of the Rayleigh lengths z and z
Rx Ry
2Δz
a
Δz =
r
zz+
RRxy
3.15
coherence
characteristic of an electromagnetic wave where there is a constant phase relationship between
each point
3.15.1
temporal coherence
characteristic of the correlation of the phases of an electromagnetic wave for different times at the
same location
3.15.2
spatial coherence
characteristic of the correlation of the phases of an electromagnetic wave at different locations at the
same time
3.16
coherence length
l
c
distance in beam direction within which the radiation emitted by the laser retains a significant phase
relationship
Note 1 to entry: It is given by c/Δv where c is the velocity of light and Δv is the frequency bandwidth of the
H H
emitted laser light.
3.17
coherence time
τ
c
time interval within which the radiation emitted by the laser retains significant phase relationship
...