SIST EN ISO 13694:2000
(Main)Optics and optical instruments - Lasers and laser-related equipment - Test methods for laser beam power (energy) density distribution (ISO 13694:2000)
Optics and optical instruments - Lasers and laser-related equipment - Test methods for laser beam power (energy) density distribution (ISO 13694:2000)
This Standard 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 test methods given in this standard are intended to be used for testing and characterization of both cw and pulsed laser beams.
Optik und optische Instrumente - Laser und Laseranlagen -Prüfverfahren für die Leistungs-(Energie-)dichteverteilung von Laserstrahlen (ISO 13694:2000)
Diese Internationale Norm legt Verfahren zur Messung der Leistungs-(Energie-) dichteverteilung fest und definiert Parameter zur Charakterisierung der räumlichen Eigenschaften von Leistungs-(Energie-) dichteverteilungsfunktionen in einer gegebenen Ebene. Die in dieser Norm beschriebenen Prüfverfahren sind zur Prüfung und Charakterisierung der Strahlen von Dauerstrichlasern wie auch von Pulslasern bestimmt.
Optique et instruments d'optique - Lasers et équipements associés aux lasers - Méthodes d'essai de distribution de puissance (d'énergie) du faisceau laser (ISO 13694:2000)
Optika in optični instrumenti - Laserji in laserska oprema - Preskusne metode za gostoto porazdelitve moči žarka (energije) (ISO 13694:2000)
General Information
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Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 13694:2000
01-november-2000
2SWLNDLQRSWLþQLLQVWUXPHQWL/DVHUMLLQODVHUVNDRSUHPD3UHVNXVQHPHWRGH]D
JRVWRWRSRUD]GHOLWYHPRþLåDUND HQHUJLMH ,62
Optics and optical instruments - Lasers and laser-related equipment - Test methods for
laser beam power (energy) density distribution (ISO 13694:2000)
Optik und optische Instrumente - Laser und Laseranlagen -Prüfverfahren für die
Leistungs-(Energie-)dichteverteilung von Laserstrahlen (ISO 13694:2000)
Optique et instruments d'optique - Lasers et équipements associés aux lasers -
Méthodes d'essai de distribution de puissance (d'énergie) du faisceau laser (ISO
13694:2000)
Ta slovenski standard je istoveten z: EN ISO 13694:2000
ICS:
31.260 Optoelektronika, laserska Optoelectronics. Laser
oprema equipment
SIST EN ISO 13694:2000 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 13694:2000
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SIST EN ISO 13694:2000
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SIST EN ISO 13694:2000
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SIST EN ISO 13694:2000
INTERNATIONAL ISO
STANDARD 13694
First edition
2000-04-01
Optics and optical instruments — Lasers
and laser-related equipment — Test
methods for laser beam power [energy]
density distribution
Optique et instruments d'optique — Lasers et équipements associés aux
lasers — Méthodes d'essai de distribution de la densité de puissance
[d'énergie] du faisceau laser
Reference number
ISO 13694:2000(E)
©
ISO 2000
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SIST EN ISO 13694:2000
ISO 13694:2000(E)
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ii © ISO 2000 – All rights reserved
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SIST EN ISO 13694:2000
ISO 13694:2000(E)
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
3.3 Distribution fitting.6
4 Coordinate system.7
5 Characterizing parameters derived from the measured spatial distribution .7
6 Distribution fitting.7
6.1 General.7
6.2 Fitting procedures .8
7 Test principle.9
8 Measurement arrangement and test equipment.9
8.1 General.9
8.2 Preparation.9
8.3 Control of environment .10
8.4 Detector system.10
8.5 Beam-forming optics, optical attenuators and beam splitters .10
9 Test procedures.11
9.1 Equipment preparation .11
9.2 Detector calibration procedure .11
9.3 Data recording and noise correction.12
10 Evaluation.13
10.1 Choice and optimization of integration limits.13
10.2 Control and optimization of background corrections.13
11 Test report .14
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SIST EN ISO 13694:2000
ISO 13694:2000(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 3.
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 International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 13694 was prepared by Technical Committee ISO/TC 172, Optics and optical
instruments, Subcommittee SC 9, Electro-optical systems.
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SIST EN ISO 13694:2000
ISO 13694:2000(E)
Introduction
Many applications of lasers involve using the near-field as well as the far-field power [energy] density distribution of
1�
the beam . The power [energy] density distribution of a laser beam is characterized by the spatial distribution of
irradiant power [energy] density with lateral displacement in a particular plane perpendicular to the direction of
propagation. In general, the power [energy] density distribution of the beam changes along the direction of
propagation. Depending on the 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.
This International Standard 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.
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 power [energy]; the other is based on
determining the spatial moments of the power [energy] density distribution of the laser beam.
The use of spatial moments is necessary for calculating the beam propagation factor K and the times-diffraction-
2
limit factor M from measurements of the beam widths at different distances along the propagation axis. ISO 11146
describes this measurement procedure. For other applications, other definitions for the beam diameter may be
used. For some quantities used in this International Standard, the first definition (encircled power [energy]) is more
appropriate and easier to use.
1� For the purposes of this International Standard, "near-field" is defined as the radiation field of a laser at a distance z from the
beam waist which is less than the Rayleigh-length z . "Far-field" is defined in ISO 11145.
R
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SIST EN ISO 13694:2000
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SIST EN ISO 13694:2000
INTERNATIONAL STANDARD ISO 13694:2000(E)
Optics and optical instruments — Lasers and laser-related
equipment — Test methods for laser beam power [energy] density
distribution
1 Scope
This International Standard 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 International Standard 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.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 11145:1994, Optics and optical instruments — Laser and laser-related equipment — Vocabulary and symbols.
ISO 11146:1999, Lasers and laser-related equipment — Test methods for laser beam parameters — Beam widths,
divergence angle and beam propagation factor.
ISO 11554:1998, Optics and optical instruments — Lasers and laser-related equipment — Test methods for laser
beam power, energy and temporal characteristics.
IEC 61040:1990, Power and energy measuring detectors — Instruments and equipment for laser radiation.
3 Terms and definitions
For the purposes of this International Standard, the terms and definitions given in ISO 11145 and IEC 61040 and
the following apply.
3.1 Measured quantities
3.1.1
power density
E(x,y,z)
part of the beam power at location z which impinges on the area �A at the location (x,y) divided by the area �A
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ISO 13694:2000(E)
3.1.2
energy density
H(x,y,z)
part of the beam energy (time-integrated power) at location z which impinges on the area �A
at the location (x,y)dividedbythearea �A
H(,x yz, ) � E(,x yz, )dt
z
3.1.3
power
P(z)
power in a continuous wave (cw) beam at location z
Pz() � E x,,y z dxdy
af
zz
3.1.4
pulse energy
Q(z)
energy in a pulsed beam at location z
Qz()� H(x,y,z)ddx y
zz
3.1.5
maximum power [energy] density
E (z)[H (z)]
max max
maximum of the spatial power [energy] density distribution function E(x,y,z)[H(x,y,z)] at location z
3.1.6
location of the maximum
(x , y , z)
max max
location of E (z)or H (z)inthe xy plane at location z
max max
NOTE (x , y , z) may not be uniquely defined when measuring with detectors having a high spatial resolution and a
max max
relatively small dynamic range.
3.1.7
threshold power [energy] density
E (z)[H (z)]
�T �T
afraction� of the maximum power [energy] density at location z
E (z)=�E (z) for cw-beams;
�T max
H (z)=�H (z) for pulsed beams;
�T max
0 � �<1
NOTE Usually the value of � chosen is such that E or H is just greater than detector background noise peaks at the
�T �T
time of measurement. Subclause 9.3 describes background noise subtraction methods used to determine detector zero levels.
Circumstances such as the application involved, distribution type, detector sensitivity, linearity, saturation, baseline, offset level,
etc., may also dictate the choice of�.
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SIST EN ISO 13694:2000
ISO 13694:2000(E)
3.2 Characterizing parameters
3.2.1
effective power [energy]
P (z)[Q (z)]
� �
P(z)[Q(z)] evaluated by summing only over locations (x,y)for which E(x,y)> E [H(x,y)> H ]
�T �T
3.2.2
fractional power [energy]
f (z)
�
fraction of the effective power [energy] for a given � to the total power [energy] in the distribution at location z
Pz()
�
fz()� for cw-beams;
�
Pz()
Qz()
�
fz()� for pulsed beams;
�
Qz()
0 � f (z) � 1
�
3.2.3
centre of gravity
centroid position
(,xy)
first linear moments at location z
NOTE For a more detailed definition, see ISO 11145.
3.2.4
beam widths
d (z), d (z)
�x �y
widths d (z) and d (z) of the beam in the x and y directions at z, equal to four times the square root of the second
�x �y
linear moments of the power [energy] density distribution about the centroid
NOTE 1 For a more detailed definition, see ISO 11145 and ISO 11146.
NOTE 2 The provisions of ISO 11146 apply to definitions and measurement of:
a) second moment beam widths d and d ;
�x �y
b) beam widths d and d in terms of the smallest centred slit width that transmits u % of the total power [energy] density
x,u y,u
(usually u = 86,5);
c) scanning narrow slit measurements of beam widths d and d in terms of the separation between positions where the
x,s y,s
transmitted power density is reduced to 0,135E ;
P
d) measurements of beam widths d and d in terms of the separation between 0,84P and 0,16P obscuration positions of a
x,k y,k
movable knife-edge;
e) correlation factors which relate these different definitions and methods for measuring beam widths.
3.2.5
beam ellipticity [eccentricity]
�(z)[e(z)]
parameter for quantifying the circularity or squareness (aspect ratio) of a distribution at z
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ISO 13694:2000(E)
d
�y
beam ellipticity �()z � ;
d
�x
22
dd�
��xy
beam eccentricity ez()�
d
�x
where the direction of x is chosen to be along the major axis of the distribution so d � d .
�x �y
NOTE If e � 0,5 or � � 0,87, rotationally symmetric distributions can be regarded as circular and rectangular-types as
square.
3.2.6
beam cross-sectional area
A (z)
�
2
Ad� � /4 for beam with circular cross-section;
��
Ad���4 d for beam with elliptical cross-section
��xy�
3.2.7
effective irradiation area
i
Azaf
�
irradiation area at location z for which the power [energy] density exceeds the threshold power [energy] density
NOTE 1 To allow for distributions of all forms, for example hollow "donut" types, the effective irradiation area is not defined in
terms of the beam widths d or d .
�x �y
NOTE 2 See threshold power [energy] density (3.1.7).
3.2.8
effective average power [energy] density
E (z)[H (z)]
� �
spatially averaged power [energy] density of the distribution at location z, defined as the weighted mean:
P
�
Ez()� for cw-beams;
�
i
A
�
Q
�
Hz()� for pulsed beams
�
i
A
�
NOTE E (z) and E (z) (see 3.1.7) refer to different parameters.
� �T
3.2.9
flatness factor
F (z)
�
ratio of the average power [energy] density to the maximum power [energy] density of the distribution at location z
E
�
Fz()� for cw-beams;
�
E
max
H
�
Fz()� for pulsed beams
�
H
max
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SIST EN ISO 13694:2000
ISO 13694:2000(E)
0< F � 1
�
NOTE For a power [energy] density distribution having a perfectly flat top F =1.
�
3.2.10
beam uniformity
U (z)
�
normalized root mean square (r.m.s.) deviation of power [energy] density from its average value at location z
11
2
U��[Exy( , ) E ] ddx y for cw-beams
� �
zz
i
E
A
�
�
11
2
U��[Hx( ,y) H ] ddx y for pulsed beams
� �
zz
i
H
A
�
�
NOTE 1 U = 0 indicates a completely uniform distribution having a profile with a flat top and vertical edges. U is expressed
� �
as either a fraction or a percentage.
NOTE 2 By using integration over the beam area between set threshold limits, this definition allows for arbitrarily shaped
beam footprints to be quantified in terms of their uniformity. Hence uniformity measurements can be made for different fractions
of the total beam power [energy] without specifically defining a windowing aperture or referring to the shape or size of the
distribution. Thus using the equations in 3.2.2 and 3.2.10, statements such as: "Using a setting� = 0,3, 85 % of the beam power
[energy] was found to have a uniformity of � 4,5 % r.m.s. from its mean value at z" can be made without reference to the
distribution shape, size, etc.
3.2.11
plateau uniformity
U (z)
P
�for distributions having a nearly flat-top profile�
�E
FWHM
Uz()� for cw-beams;
P
E
max
�H
FWHM
Uz()� for pulsed beams
P
H
max
where �E [�H ] is the full-width at half-maximum (FWHM) of the peak near E [H ] of the power
FWHM FWHM max max
[energy] density histogram N(E)[N(H )], i.e. the number of (x,y) locations at which a given power [energy] density
i i
E [H ] is recorded.
i i
NOTE 0 < U (z)<1; U (z)� 0 as distributions become more flat-topped.
P P
3.2.12
edge steepness
s(z)
i i
normalized difference between effective irradiation areasAz() andAz() with power [energy] density values
01, 09,
above 0,1E (z)[0,1H (z)] and 0,9E (z)[0,9H (z)] respectively
max max max max
ii
Az()�A ()z
01,,0 9
sz() �
i
Az()
01,
0< s(z)<1
NOTE s(z)� 0 as the edges of the distribution become more vertical.
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SIST EN ISO 13694:2000
ISO 13694:2000(E)
i
Parameters E , E , P , A , F , U , and s are illustrated in Figure 1 for a uniform power density distribution in one
max � � � � �
dimension.
Figure 1 — Illustration for a uniform power density distribution E(x) in one dimension
3.3 Distribution fitting
3.3.1
roughness of fit
R
maximum deviation of the theoretical fit to the measured distribution
f
EE�
ij ij
max
R�
E
max
f
where E is the fitted theoretical distribution
0� R � 1
NOTE As R� 0 the fit becomes better.
3.3.2
goodness of fit
G
parameter based upon Kolomogorov-Smirnov statistical test characterizing the fit between measured and
theoretical distributions
1
G�
1�� N
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SIST EN ISO 13694:2000
ISO 13694:2000(E)
where
N is the total number of data points in the measured distribution.
� is the maximum deviation between measured and theoretical distributions of apertured powers (energies)
truncated at n� 10 random locations (x , y ) in the distribution:
i j
f
PP�
ij ij
max
� �
P
yy� yy�
xx� xx�
j j
i i
ff
PE� (,xy)ddxy and PE� (,xy)ddxy
ij ij
zz zz
xx� yy� xx� yy�
i j i j
f
where E is the fitted theoretical distribution
0� G� 1
NOTE As G�1(�� 0) the quality of the fit becomes better.
4 Coordinate system
The x, y, z Cartesian axes define the orthogonal space directions in the beam axes system. The x and y axes are
transverse to the beam and define the transverse plane. The beam propagates along the z axis. The origin of the z
axis is in a reference xy plane defined by the laser manufacturer, e.g. the front of the laser enclosure. For elliptical
beams, the principal axes of the distribution coincide with the x and y axes, respectively. In cases for which the
principal axes of the distribution are rotated with respect to the laboratory coordinate system, the provisions of
ISO 11146 describing coordinate rotation through an azimuth angle� into the laboratory system shall apply.
5 Characterizing parameters derived from the measured spatial distribution
In definitions 3.2.1 to 3.2.12, summation integrals shall be computed over all locations (x,y)for which E(x,y)> E or
�T
H(x,y)> H . This “threshold clipping” procedure for truncating summation integrals is different from the 99 %
�T
power [energy] spatial aperture truncation method used for calculating second-moment beam widths in ISO 11146.
Before using threshold clipping it is necessary to apply proper background subtraction to the measured signal.
According to the note in 3.1.7 usually the value of � is chosen such that E or H is just greater than detector
�T �T
background noise peaks at the time of measurements.
NOTE Since practical laser beams have a finite lateral size and detectors which measure their power density distribution a
finite spatial resolution, definitions in this International Standard used for computations should more precisely contain discrete
finite sums rather than continuous integrals. Finite integrals are used because they have a more compact form than summations
and it is common practice to do so. For further information on the choice of practical integration limits, refer to 10.1.
6 Distribution fitting
6.1 General
For pulsed lasers, the following substitutions shall be made in the text of 3.3: power density E by energy density H,
f f
power P by energy Q and fitted theoretical distribution E by H respectively.
Testing for goodness of fit shall be carried out only over regions of the detector for which signal data has been
registered. Values of G < 0,5 imply a poor fit which should be rejected.
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SIST EN ISO 13694:2000
ISO 13694:2000(E)
Figure 2 illustrates parameters R and� for a power density distribution in one-dimension.
Key
1 E(x) measured distribution
f
2 E (x) theoretical Gaussian fit (R =0,16; G = 0,81)
� maximum difference in apertured powers
R maximum difference in power densities
Figure 2 — Example of Gaussian fitting to a measured distribution E(x) in one-dimension
6.2 Fitting procedures
2�
For fitting theoretical to measured distributions, the following approach is preferred to least-squared methods .The
��
measurement fixes five parameters: the centroid location (,xy),beam widths d and d and total beam power
�x �y
[energy], P [Q]. These are then used as best estimates for the centre, standard deviation and normalization (area
f
under the curve) respectively of the theoretical distribution E (x,y)
Examples of the functional form of common distributions which may be fitted are:
2n
1
� r
f f
2
Ex(,y)�E e
0
2
16nP
f
where E �
0
1
2
n
1
2 �()dd
2n ��xy
n
2
2
L O
R U
R U
44()xx� |(yy�)|
2n
M P
and r � �
S V S V
M P
d d
| |
��xy
T W
T W
N Q
2� Least-squared methods of fitting place equal weight on all regions of the distribution. For many distributions equal weighting
of the wings and central region may not be appropriate.
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SIST EN ISO 13694:2000
ISO 13694:2000(E)
8P
f
Gaussian: when order n =1,so
E �
0
πdd
��xy
SuperGaussian: when order n = 2, 3,.
1 2n
� r
f f 2n
2
Donut and SuperDonut: Ex(,y)�E r e
0
P
f
Uniform (flat-top, top-hat or rectangular): Ex(,y)� for locations (x,y)where E(x,y)> E
T
i
A
�
= 0 elsewhere
i
For fitting uniform distributions, the value of A obtained for the measured distribution should be used.
�
Cross-sections of measured distributions shall be fitted using one-dimensional forms of these theoretical
distributions. The linear and azimuthal coordinates of cross-sections shall then be stated.
7 Test principle
First the power [energy] density distribution E(x,y)[or H(x,y)] at the location z is measured by positioning a spatially
resolving detector of irradiance directly in the beam. The detector plane is either placed directly at z normal to the
beam propagation direction or a suitable optical imaging system is used to relay the plane at z onto the detector. A
stationary power [energy] density distribution is required to be measured. For lasers with temporally fluctuating
beams an average power [energy] density shall be used. Following the measurement of E(x,y)[or H(x,y)],
parameters that characterize the beam power [energy] density distribution are then calculated from definitions
givenin3.2.
8 Measurement arrangement and test equipment
8.1 General
For measuring the power [energy] density distribution of laser beams, any measuring device can be used which
provides high spatial resolution and high dynamic range.
Methods commonly used to quantify laser beam power density distributions include 1D and 2D matrix camera
arrays, single- and dual-axis scanning pinholes, single-axis scanning slits or knife edges, transmission through
variable apertures (power-in-a-bucket measurements) and 2D densitometry by reflectance, fluorescence,
phosphorescence, and film exposure.
8.2 Preparation
The laser beam and the optical axis of the measuring system should be coaxial. Suitable optical alignment devices
are available for this purpose. Any pointing variations of the beam during the measurement period shall be verified
not to affect the accuracy required of the measurement.
Optical elements such as beam splitters, attenuators, relay lenses shall be mounted such that the optical axis runs
through their geometric centres. Care should be taken to avoid systematic errors. Reflections, external ambient
light, thermal radiation or air draughts are all potential sources of error.
The field of view of the optical system shall be such that it accommodates the entire cross-section of the laser
beam. Clipping or diffraction loss shall be smaller than 1 % of the total beam power or energy.
After the initial preparation is complete, an evaluation to determine if the entire laser beam reaches the detector
surface shall be made. For testing this, apertures of different diameters can be introduced into the beam path in
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SIST EN ISO 13694:2000
ISO 13694:2000(E)
front of each optical component as well as the detector itself. The aperture which reduces the laser power by 5 %
should have a diameter less than 0,8 times the aperture of the optical component.
8.3 Control of environment
Suitable measures, such as mechanical and acoustical isolation of the test set-up, shielding from extraneous
radiation, temperature stabilization of the laboratory, choice of low-noise amplifiers, shall be taken to ensure that
the contribution to the total probable error in the parameter to be measured is low.
Care should be taken to ensure that the atmospheric environment in high power [energy] laser beam paths does
not contain gases or vapours that can absorb the laser radiation and cause thermal distortion to the beam power
[energy] density distribution that is being measured.
8.4 Detector system
Measuring parameters of the power [energy] density distribution requires the use of a power [energy] meter having
a high spatial res
...
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