ISO 6760-1:2024

Optics and photonics — Test method for temperature coefficient of refractive index of optical glasses — Part 1: Minimum deviation method

This document specifies the measurement method used for calculating the temperature coefficient of the refractive index by measuring the refractive index, which changes with the temperature of the optical glass using the minimum deviation method. The intended temperature range for the specified measurement method is –40 °C to +80 °C. The intended wavelength range for the specified measurement method is 365 nm to 1 014 nm. The intended accuracy for the specified measurement method is 1 × 10-6 K-1.

Optique et photonique — Méthode d'essai pour déterminer le coefficient de température de l'indice de réfraction des verres optiques — Partie 1: Méthode de la déviation minimale

General Information

• Status: Published
• Publication Date: 05-May-2024
• ICS: 37.020 - Optical equipment
• Technical Committee: ISO/TC 172/SC 3 - Optical materials and components
• Drafting Committee: ISO/TC 172/SC 3 - Optical materials and components
• Current Stage: 9092 - International Standard to be revised
• Completion Date: 21-Aug-2024

Standards Content (Sample)

International
Standard
ISO 6760-1
First edition
Optics and photonics — Test
2024-05
method for temperature coefficient
of refractive index of optical
glasses —
Part 1:
Minimum deviation method
Optique et photonique — Méthode d'essai pour déterminer le
coefficient de température de l'indice de réfraction des verres
optiques —
Partie 1: Méthode de la déviation minimale
Reference number
© ISO 2024
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Measuring apparatus . 3
5.1 Goniometer .3
5.2 Light source .3
5.3 Detector .3
5.4 Thermal chamber .3
6 Specimen prism . 4
7 Measurement . 4
7.1 Measurement of apex angle . .4
7.2 Measurement of the angle of minimum deviation .4
8 Calculation . 5
8.1 Absolute refractive index .5
8.2 Temperature coefficient of absolute refractive index .6
8.3 Temperature coefficient of relative refractive index .7
9 How to express the temperature coefficient of refractive index . 8
10 Test report . 8
Annex A (informative) Formula for calculating the refractive index of air . 9
Annex B (informative) Calculation method for obtaining the relative refractive index of glass
at an arbitrary temperature, air pressure and relative humidity .11
Annex C (informative) Half prism method .13
Annex D (informative) Interpolation formula for Δn/ΔT .18
Annex E (informative) Derivation and verification of Δn /ΔT . 19
rel
Bibliography .22

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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with the International Electrotechnical Commission (IEC) on all matters of 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.
A list of all parts in the ISO 6760 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
Introduction
Optical glass is widely used in optical devices such as cameras, telescopes, and microscopes, and its refractive
index is measured by the minimum deviation method (see ISO 21395-1) and the V-block refractometer
[4]
method (see ISO 21395-2 ). Here, when designing an optical apparatus that requires high resolution, it
is necessary to consider the temperature change of the refractive index of the optical glass in the usage
environment, however up until now, there is no International Standard. In view of the above situation,
this document proposes a method for measuring the temperature coefficient of refractive index of optical
glass with high accuracy, aiming to help mutual understanding of measured value users and contribute to
efficiency and fairness.
v
International Standard ISO 6760-1:2024(en)
Optics and photonics — Test method for temperature
coefficient of refractive index of optical glasses —
Part 1:
Minimum deviation method
1 Scope
This document specifies the measurement method used for calculating the temperature coefficient of the
refractive index by measuring the refractive index, which changes with the temperature of the optical glass
using the minimum deviation method.
The intended temperature range for the specified measurement method is –40 °C to +80 °C.
The intended wavelength range for the specified measurement method is 365 nm to 1 014 nm.
-6 -1
The intended accuracy for the specified measurement method is 1 × 10 K .
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 21395-1:2020, Optics and photonics — Test method for refractive index of optical glasses — Part 1: Minimum
deviation method
3 Terms and definitions
For the purposes of this document, 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/
3.1
temperature coefficient of refractive index
ratio of refractive index change to temperature change at a selected wavelength
[2]
Note 1 to entry: Similar to ISO 9802 .
3.2
temperature coefficient of absolute refractive index
Δn /ΔT
abs
ratio of refractive index change in vacuum to temperature change at a selected wavelength
[2]
[SOURCE: ISO 9802:2022 , 3.4.2.3]

3.3
temperature coefficient of relative refractive index
Δn /ΔT
rel
ratio of refractive index change at an air pressure of 1,013 3 × 10 Pa and a relative humidity of 0 % to
temperature change at a selected wavelength
[2] 5
[SOURCE: ISO 9802:2022 , 3.4.2.4, modified — 1,013 3 × 10 Pa and a relative humidity of 0 %.]
Note 1 to entry: This definition of Δn /ΔT is for a specific pressure and humidity. Δn /ΔT can be calculated for any
rel rel
other pressure and humidity by understanding the index of air in those conditions.
3.4
thermal chamber
chamber where the temperature of the specimen can be changed and maintained to a preset temperature
4 Principle
As shown in Figure 1, a specimen prism is placed in a thermal chamber. The temperature of the specimen
prism is changed from T to T or from T to T , and the refractive index of the specimen prism is measured at
1 2 2 1
the temperatures of T and T respectively, in accordance with the method described in ISO 21395-1 to find
1 2
the temperature coefficient of refractive index. Figure 2 shows the concept of calculating this temperature
coefficient of refractive index.
NOTE 1 In this document the term “light” is used to describe not only optical radiation visible to the human eye but
also radiation in the infrared and ultraviolet spectrum.
NOTE 2 In this document, all temperature symbols are represented by "T". The original symbol for temperature in
ISO 80000-5 is "t" or "ϑ " for temperature in Celsius degrees, and "T" for absolute temperature.
NOTE 3 Alternatively the measurement principle according to Annex C can be applied.
Key
1 light source 7 thermal chamber containing the specimen prism
2 collimator 8 specimen prism
3 incident light 9 transmitted light
4 goniometer containing the telescope and detector 10 telescope
5 window 11 detector
6 rotating stage containing the thermal chamber 12 thermometer
Figure 1 — Measurement set-up with thermal chamber

Δn nn−
=
ΔT TT−
Key
X temperature
Y refractive index
T , T temperature of specimen prism
1 2
n refractive index of specimen prism at temperature T
1 1
n refractive index of specimen prism at temperature T
2 2
Figure 2 — Conceptual diagram for calculation of temperature coefficient of refractive index
5 Measuring apparatus
5.1 Goniometer
The goniometer shall
...