ISO 9211-2:2024

International
Standard
ISO 9211-2
Third edition
Optics and photonics — Optical
2024-02
coatings —
Part 2:
Optical properties
Optique et photonique — Traitements optiques —
Partie 2: Propriétés optiques
Reference number
© ISO 2024
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ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Optical properties to be specified . 1
5 Measurement conditions . 2
6 Numerical specification and graphical representation of spectral characteristics . 2
6.1 General .2
6.2 Rules for the numerical specification of spectral characteristics .2
6.3 Rules for the graphical representation of spectral characteristics.3
6.4 Graphical representation of principal optical functions .4
6.4.1 General .4
6.4.2 Reflecting function (RE) .4
6.4.3 Antireflecting function (AR) .5
6.4.4 Beam splitting function (BS) .6
6.4.5 Attenuating function (AT) . .7
6.4.6 Filtering function (FI) .8
6.4.7 Selecting or combining function (SC) .10
6.4.8 Polarizing function (PO) . 12
6.4.9 Phase changing function (PC) . 13
6.4.10 Absorbing function (AB) .14
Annex A (normative) Supplementary terms and definitions for filtering and selecting functions .16

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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This document was prepared by Technical Committee ISO/TC 172, Optics and Photonics, Subcommittee SC 3,
Optical materials and components.
This third edition cancels and replaces the second edition (ISO 9211-2:2010), which has been technically
revised.
The main changes are as follows:
— additional symbols (T, R, and A) for transmittance, reflectance and absorption added;
— definitions have been provided for average spectral characteristics;
— default wavelength units of nm added;
— more examples are provided;
— text added and modified for clarity;
— the use of the symbols of Annex A have been generalized.
A list of all parts in the ISO 9211 series can be found on the ISO website.
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
International Standard ISO 9211-2:2024(en)
Optics and photonics — Optical coatings —
Part 2:
Optical properties
1 Scope
This document indicates how to specify optical properties of coatings and to represent their spectral
characterization graphically in the ISO 9211 series, which defines the specifications for optical coatings
excluding ophthalmic optics (spectacles). It defines the general characteristics and the test and measurement
methods whenever necessary, but is not intended to define the process method.
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 9211-1, Optics and photonics — Optical coatings — Part 1: Vocabulary
ISO 15368, Optics and photonics — Measurement of reflectance of plane surfaces and transmittance of plane
parallel elements1
ISO 19962, Optics and photonics — Spectroscopic measurement methods for integrated scattering by plane
parallel optical elements
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 9211-1 and the following terms
and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Optical properties to be specified
When specifying optical properties, the refractive indices of the incident medium and the emergent medium
shall be given. The polarization state of the incident radiation shall also be indicated if the angle of incidence,
θ, is different from zero or a range of angles of incidence is given. If there is no indication of polarization,
unpolarized radiation is assumed.
The optical properties τ(λ), ρ(λ), α(λ) (or alternatively T(λ), R(λ) and A(λ)), D(λ) and ΔΦ(λ) of a coating
shall be specified by using the formulation given and explained in 6.2 in order to provide a comprehensive
description of a coating with regard to its minimum set of optical properties. Other optical properties such
as scattering or colorimetric parameters etc. shall be subject to agreement between manufacturer and
customer if appropriate.
If the coating optical properties are required to be achieved at a specific temperature or range of
temperatures, this shall be indicated with a note.

5 Measurement conditions
The measurement conditions for the spectrophotometric characterization shall be in accordance with
ISO 15368, ISO 19962 or an equivalent method. These conditions depend on the principle of the measurement
method and the instruments used, including the angle of incidence, the state of polarization, the spectral
range and bandwidth of the measurement beam, etc. and shall be recorded in sufficient detail to enable
verification of the measurement.
6 Numerical specification and graphical representation of spectral characteristics
6.1 General
This document defines the rules for the spectrophotometric characterization of optical coatings. If no units
are given for wavelength, the units are assumed to be nanometres. The limit values of τ, ρ and α are unitless.
6.2 Rules for the numerical specification of spectral characteristics
The general structure of a numerical specification, as distinguished from a graphical specification, of a
spectral optical property shall follow the structure of an inequality with the following terms:
(lower limit term) < or ≤ (spectral optical property term) < or ≤ (upper limit term).
If both a lower limit term and an upper limit term are used, the lower limit will always come first. If a specific
wavelength increment has to be used, this shall be specified in a note.
EXAMPLE 1 0,85 < ρ(380 nm to 450 nm, 45°) < 0,95
The subscript “ave” or “avg” is used to denote the spectral characteristic average across the spectral band.
If no subscript is used, the spectral characteristic is required to meet the specification at all wavelengths in
the specified spectral band.
EXAMPLE 2 1,9 ≤ D (350 nm to 1 100 nm) ≤ 2,1
ave
If a range of angles is indicated, the spectral characteristic is required to meet the specification over all
angles indicated. If a specific angle increment is to be used, this shall be specified in a note.
EXAMPLE 3 0,45 ≤ τ(1,064 µm, 35° to 55°) < 0,65
The inequality may contain only two terms if the spectral optical property needs to be bounded only on one
side. If no units are given for the wavelength range, the wavelengths are assumed to be in nm.
EXAMPLE 4 R(400 to 700, 0° to 35°) ≤ 0,02
If only a lower limit term is used, the comparator sign may be reversed for clarity
EXAMPLE 5 τ (0,4 µm to 0,65 µm) ≥ 0,98
avg
If a range of angles is indicated with a spectral characteristic average, the spectral characteristic average is
required to meet the specification over all angles. If the spectral characteristic is intended to be averaged
over both wavelength and angle, this shall be indicated with a note.
EXAMPLE 6 R (0,38 µm to 0,95 µm, 0° to 10°) ≤ 0,04
ave
An arrow (→) is used to indicate a linear change of the specification over the indicated spectral range.
EXAMPLE 7 0,75 → 0,60 < α (700 nm to 1 100 nm) < 0,90 → 0,75
Table 1 gives a schematic representation of elements necessary for the numerical specification of spectral
characteristics, where (upper case) Z is used to indicate the coating property such as τ, ρ, etc., and (lower
case) z indicates a lower or upper allowed value of Z. A coating may require more than one spectral
characteristic specification. Specific examples for some common coating types are shown in Table 2.

Table 1 — Scheme of elements for the numerical specification of spectral characteristics
Wavelength
(or wavenumber)
Spectral Z
Lower limit Comparator range or single wave- Comparator Upper limit
optical represents
(subscript L) sign length sign (subscript U)
property any of
(or wavenumber),
a
angle of incidence
i = 1, 2, . i = 1, 2, . i = 1, 2, .
τ, ρ, α , D,
z < or ≤ Z (λ to λ , θ) or (λ , θ) < or ≤ z
Li i i+1 i Ui
ΔΦ or δΦ
τ, ρ, α, D,
b b
z → z < or ≤ Z (λ to λ , θ) < or ≤ z → z
Li
...