SIST EN ISO 11551:2004

SLOVENSKI STANDARD
SIST EN ISO 11551:2004
01-februar-2004
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Optics and optical instruments - Lasers and laser-related equipment - Test method for
absorptance of optical laser components (ISO 11551:2003)
Optik und optische Instrumente - Laser und Laseranlagen - Prüfverfahren für den
Absorptionsgrad von optischen Laserkomponenten (ISO 11551:2003)
Optique et instruments d'optique - Lasers et équipements associés aux lasers - Méthode
d'essai du facteur d'absorption des composants optiques pour lasers (ISO 11551:2003)
Ta slovenski standard je istoveten z: EN ISO 11551:2003
ICS:
31.260 Optoelektronika, laserska Optoelectronics. Laser
oprema equipment
SIST EN ISO 11551:2004 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 11551:2004

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SIST EN ISO 11551:2004


INTERNATIONAL ISO
STANDARD 11551
Second edition
2003-12-01


Optics and optical instruments — Lasers
and laser-related equipment — Test
method for absorptance of optical laser
components
Optique et instruments d'optique — Lasers et équipements associés
aux lasers — Méthode d'essai du facteur d'absorption des composants
optiques pour lasers




Reference number
ISO 11551:2003(E)
©
ISO 2003

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SIST EN ISO 11551:2004
ISO 11551:2003(E)
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ii © ISO 2003 — All rights reserved

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SIST EN ISO 11551:2004
ISO 11551:2003(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 1
4 Symbols and units of measure. 2
5 Preparation of test sample and measuring arrangement . 2
6 Characteristic features of the laser radiation . 3
7 Test procedure . 4
8 Evaluation . 5
9 Test report . 7
Annex A (informative) Effects changing absorptance. 9
Annex B (informative) Influence of signal distortions . 10
Annex C (informative) Algorithm for parameterizing the temperature data . 13

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SIST EN ISO 11551:2004
ISO 11551:2003(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 2.
The main task of technical committees is to prepare International Standards. 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 document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 11551 was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee SC 9,
Electro-optical systems.
This second edition cancels and replaces the first edition (ISO 11551:1997), which has been technically
revised.
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SIST EN ISO 11551:2004
ISO 11551:2003(E)
Introduction
To characterize an optical component, it is important to know its absorptance. When radiation impinges upon
a component, a part of that radiation is absorbed, increasing the temperature of the component. In this
International Standard only the part of the absorbed power/energy that is converted into heat is measured. If
enough energy is absorbed, the optical properties of the component may be changed, and the component
may even be destroyed. Absorptance is the ratio of the radiant flux absorbed to the radiant flux of the incident
radiation.
In the procedures described in this International Standard, the absorptance is determined calorimetrically as
the ratio of power or energy absorbed by the component to the total power or energy, respectively, impinging
upon the component. The assumption is made that the absorptance of the test sample is constant within the
temperature fluctuations experienced by the component during the measurement and is independent of both
the position of the irradiating beam on the sample surface and the power density of the impinging radiation.
For several bulk materials like CdTe, the absorptance depends on the position of the irradiating beam on the
sample surface. Several infrared materials exhibit a strong dependence of absorptance on temperature,
especially at high temperatures.
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SIST EN ISO 11551:2004
INTERNATIONAL STANDARD ISO 11551:2003(E)

Optics and optical instruments — Lasers and laser-related
equipment — Test method for absorptance of optical laser
components
1 Scope
This International Standard specifies procedures and techniques for obtaining comparable values for the
absorptance of optical laser components.
2 Normative references
The following referenced documents are indispensable for the application 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 31-6:1992, Quantities and units — Part 6: Light and related electromagnetic radiations
ISO 11145:2001, Optics and optical instruments — Lasers and laser-related equipment — Vocabulary and
symbols
ISO 14644-1:1999, Cleanrooms and associated controlled environments — Part 1: Classification of air
cleanliness
3 Terms and definitions
For the purposes of this document, the terms and definitions in ISO 11145 and ISO 31-6 and the following
apply.
3.1
absorptance
α
ratio of the radiant flux absorbed to the radiant flux of the incident radiation
NOTE The definition of absorptance used for this international Standard is limited to absorptance processes which
convert the absorbed energy into heat. For certain types of optics and radiation, additional non-thermal processes may
result in absorption losses which will not be detected by the test procedure described here (see Annex A).
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SIST EN ISO 11551:2004
ISO 11551:2003(E)
4 Symbols and units of measure
Table 1 — Symbols and units of measure
Symbol Term Unit
c
Thermal capacity of test sample, holder, etc. J/(kg⋅K)
i
d , d
Beam width on test sample mm
σ x σ y
m
Mass of test sample, holder, etc. kg
i
P cw power W
P
Average laser power for continuous pulse mode operation W
av
P
Typical peak power for repetitive pulse mode operation W
pk
t
Duration of irradiation s
B
∆t Time interval s
T
Ambient temperature K
amb
∆T Temperature difference K
α Absorptance 1
Angle of incidence Rad
β
γ Thermal loss coefficient 1/s
λ Wavelength nm

5 Preparation of test sample and measuring arrangement
Storage, cleaning and the preparation of the test samples are carried out in accordance with the
manufacturer’s instructions for normal use.
The environment of the testing place consists of dust-free filtered air with less than 50 % relative humidity. The
residual dust is reduced in accordance with cleanroom class 7 as defined in ISO 14644-1:1999. In this
connection, an environment free from draughts is very important in order to keep thermal disturbances and
heat loss by convection as small as possible. Measurements in ambient atmosphere and vacuum may have
different influences on the measured absorptance.
A laser shall be used as the radiation source. To keep errors as low as possible, the laser power chosen for
measurements is as high as possible but without causing any deterioration to the component.
Wavelength, angle of incidence and state of polarization of the laser radiation used for the measurement shall
correspond to the values specified by the manufacturer for the use of the test sample. If ranges are accepted
for these three quantities, any combination of wavelength, angle of incidence and state of polarization may be
chosen from those ranges.
The sample is mounted in a suitable holder. The thermal sensors are either connected directly to the sample
surface, or attached to the sample holder. Good thermal contact between sensor and sample or between
holder and sample shall be achieved. Precaution shall be taken to avoid a possible drop in thermal
conductance between temperature sensor and test sample.
In order to increase the precision of the measurements, the sample should be mounted inside a chamber
designed for thermal shielding, with apertures for the laser beam. Special attention shall be given to ensure
that the temperature measurement itself does not cause a change of the sample temperature.
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SIST EN ISO 11551:2004
ISO 11551:2003(E)
Suitable diaphragms should be placed in the beam path in front of and behind the test sample to ensure that
only the test sample is irradiated by the measuring beam and that reflected or stray radiation will not strike the
holder or the chamber walls. The number of transmissive optics employed for beam guiding should be
minimized in order to reduce possible distortions by multi-reflections or scattered radiation. The transmitted
and reflected partial beams shall be directed on to beam dumps with minimized back scatter.
Figure 1 shows a schematic measuring arrangement. The curved folding mirror M1 is recommended for
imaging the laser output window on to the sample in order to avoid diffracted radiation influencing the
measurement.

Key
1 laser 7 test sample
2 mirror M1 8 personal computer
3 optical axis 9 beam stop
4 mirror M2 10 thermal sensor
5 test chamber 11 control unit
6 sample holder 12 power detector
Figure 1 — Typical arrangement for measurement of the absorptance
6 Characteristic features of the laser radiation
The following physical quantities are needed for characterizing the laser radiation used for the test:
 wavelength λ;
 angle of incidence β ;
 state and degree of polarization;
 beam widths on the test sample d , d ;
σ x σ y
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SIST EN ISO 11551:2004
ISO 11551:2003(E)
 average power P for cw or continuously pulsed lasers;
av
 typical peak power P and pulse energy Q in the case of continuously pulsed lasers;
pk
 duration of irradiation t .
B
7 Test procedure
7.1 General
The following auxiliary tests shall be performed on a regular basis and whenever the measuring arrangement
has been altered.
7.2 Calibration
7.2.1 Calibration of the power signal
Calibrate the power signal by placing a calibrated laser power detector at the location of the test components
and, in order to obtain correct calibration, compare the measured laser power to the signal of the power
monitor used during absorptance tests.
7.2.2 Calibration of the temperature signal
Calibrate the temperature signal by fixing a test sample, to which a calibrated thermal sensor is attached, to
the sample holder. Compare the temperature signals of this calibrated detector and the sensors used during
absorptance tests while varying the ambient temperature slowly over a range of a few kelvins at the typical
test temperature.
7.2.3 Calibration of the thermal response
For certain types of sample materials and geometries, the temperature rise induced by the absorbed heat may
differ from the theoretical response expected for ideal materials having infinite thermal conductivity. In these
cases, a correction factor f shall be determined, which compensates for the influence of such phenomena on
c
the absorptance test result. f is unity if the influence of limited thermal conductivity can be neglected.
c
For calibration, a reference sample of known absorptance, which is similar to the samples under investigation
with respect to substrate geometry, heat capacity and thermal conductivity, is tested for absorptance as
described below. The irradiation time and evaluation method used for calibration shall be the same as for
other typical absorptance tests for which the calibration shall be valid.
Depending on the evaluation method used for the absorptance test, the correction coefficient can be
calculated by substituting the value of the known calibration sample absorptance for α in equations 2 (see 8.3)
or 5 (see 8.4), and solving for f .
c
NOTE 1 A known absorptance can be achieved by applying a thin, high-absorbing coating to the sample surface area
that is exposed to irradiation. High absorptance values can be determined with sufficient accuracy, e.g. by measuring the
fraction of transmitted, reflected and scattered radiation
...