ISO 19740:2018

INTERNATIONAL ISO
STANDARD 19740
First edition
2018-05
Optics and photonics — Optical
materials and components — Test
method for homogeneity of infrared
optical materials
Optique et photonique — Matériaux et composants optiques —
Méthodes d’essai pour déterminer l’homogénéité des matériaux
optiques infrarouges
Reference number
©
ISO 2018
© ISO 2018
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ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus . 3
5.1 Apparatus arrangement . 3
5.2 Optical module of interferometer . 4
5.3 Reference flat . 4
5.4 Standard mirror . 4
5.5 Image sensor . 4
5.6 Computer data collecting, processing and displaying system. 4
5.7 Thickness measurement equipment . 4
6 Test conditions . 4
6.1 Temperature . 4
6.2 Relative humidity . 4
6.3 Vibration isolation . 4
6.4 Airflow . 5
7 Sample . 5
7.1 Outline . 5
7.1.1 Wedge shaped sample . 5
7.1.2 Parallel plane sample . 5
7.2 Thickness . 5
7.3 Wedge angle. 5
7.4 Polished surfaces. 6
7.4.1 Wedge shaped sample . 6
7.4.2 Parallel plane sample . 6
8 Procedure. 6
8.1 Four-step method . 6
8.2 Two-step method . 7
9 Data processing . 7
9.1 Calculation of refractive index error distribution with the four-step method. 7
9.2 Calculation of refractive index error distribution with the two-step method . 8
9.3 Calculation of the PV value and the standard deviation value of refractive index . 8
10 Calculation of measurement value and measurement uncertainty .8
10.1 Calculation of measurement value . 8
10.2 Calculation of measurement uncertainty . 9
10.3 Frequency of measuring sample . 9
11 Expanded uncertainty of the measurement . 9
12 Test Report . 9
Annex A (informative) Infrared interferometer .11
Annex B (informative) Temperature stability for homogeneity measurements .14
Annex C (informative) Flatness of sample .16
Annex D (informative) Test record for homogeneity of infrared optical materials .18
Bibliography .19
Foreword
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electrotechnical standardization.
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This document was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee
SC 3, Optical materials and components.
iv © ISO 2018 – All rights reserved

INTERNATIONAL STANDARD ISO 19740:2018(E)
Optics and photonics — Optical materials and components
— Test method for homogeneity of infrared optical
materials
1 Scope
This document specifies the principle, apparatus, condition, sample, procedure and data processing of
measuring homogeneity of infrared optical materials.
It is applicable to the determination of homogeneity of infrared optical materials, such as infrared
optical glass, infrared crystals and infrared ceramics, which are opaque to visible wavelengths and
whose transmission optical spectra are beyond 0,78 µm.
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 10110-7, Optics and photonics — Preparation of drawings for optical elements and systems — Part 7:
Surface imperfections
ISO 10110-8, Optics and photonics — Preparation of drawings for optical elements and systems — Part 8:
Surface texture; roughness and waviness
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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 http: //www .electropedia .org/
3.1
peak-to-valley value of refractive index
PV value
∆n
PV
difference between the maximum and the minimum values of refractive index distribution of an
infrared optical material in its cross-sectional area of the definition area
3.2
standard deviation value of refractive index
∆n
STD
value which is expressed with the square root of the sum of the squares of the differences of both the
distribution values and the average value of refractive index of an infrared optical material divided by
the sampling number of the distribution
3.3
homogeneity
gradual variation of the refractive index distribution within an optical element in the prescribed
direction (mostly perpendicular to optical path) and within the prescribed cross-section
3.4
homogeneity value
level of inconsistency of the refractive index distribution of an infrared optical material in the
prescribed direction (mostly perpendicular to optical path) and within the prescribed cross-sectional
area and per unit thickness of infrared optical materials, which is expressed in the PV value and the
standard deviation value of refractive index (3.2)
4 Principle
For a wedge-shaped sample, measure with a digitalized infrared interferometer the wavefront
interferograms of the front surface and the rear surface of
...