Measurement of absorption loss of optical thin-film by infrared thermal imaging

Jing Jianhang; Kong Mingdong; Wang Qiang; Guo Chun

doi:10.12086/oee.2021.210071

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Jing J H, Kong M D, Wang Q, et al. Measurement of absorption loss of optical thin-film by infrared thermal imaging[J]. Opto-Electron Eng, 2021, 48(6): 210071. doi: 10.12086/oee.2021.210071

Citation:

Jing J H, Kong M D, Wang Q, et al. Measurement of absorption loss of optical thin-film by infrared thermal imaging[J]. Opto-Electron Eng, 2021, 48(6): 210071. doi: 10.12086/oee.2021.210071

Measurement of absorption loss of optical thin-film by infrared thermal imaging

1.
School of Optoelectronics, University of Chinese Academy of Sciences, Beijing 100049, China
2.
Optical Thin Film Technology Laboratory, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu, Sichuan 610209, China

Fund Project: National Natural Science Foundation of China (61805247), Youth Innovation Promotion Association, CAS, and Sichuan Province Science and Technology Plan

More Information

^*Corresponding author: Kong Mingdong, E-mail: kongmingdong@126.com

Received Date 15 March 2021

Revised Date 11 May 2021

Published Date 01 June 2021

Abstract

Abstract

During the preparation and use of the optical thin film, the absorption center will be generated due to defects and pollution. When the optical thin film is irradiated by a laser, the absorption center absorbs light energy and generates thermal signals, according to which the optical absorption loss of an optical film can be measured. The method proposed in this paper for measuring the optical absorption loss of a thin film based on a thermal imager. The addition of a reference sample in the test can reduce the impact of the changes of environmental temperature and the thermal imager noise on the temperature test results. Taking a certain area of the temperature field recorded by the thermal imager during the entire laser irradiation process can reduce the errors of the finite element simulation calculation caused by the laser pointing fluctuations and the unsatisfactory spot distribution. Using this method, the absorption loss of a small-size 45° high-reflection film was tested to be 7.60 ppm, and the spatial distribution of the absorption loss of the same batch of large-size optical film samples were tested. The absorption of the optical film measured by this method is consistent with the result of the laser calorimetry test. This method does not require long-term constant temperature and strict environmental temperature control, and the tested sample size is not limited.
- optical thin film /
- absorption loss /
- infrared thermography /
- finite element /
- absorption measurement

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References

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Overview

Overview

Overview: During the preparation and use of the optical thin film, the absorption center will be generated due to defects and pollution. When illuminating optical film by laser light, the absorption center will absorb light energy and effectively generate the thermal signals. There are many methods for measuring the optical absorption loss of optical films, such as the laser calorimeter method, photothermal deflection method, surface thermal lens method, and so on. These methods have some problems, such as long measurement time, the influence of scattering on optical absorption, and the high requirement of spatial light position detector. The accuracy of the infrared thermal imager has been able to measure relatively small temperature changes in recent years, which provides the possibility for the measurement of the optical thin film absorption based on the infrared thermal imager. Infrared thermal imaging has unique advantages in measuring the absorption loss of optical films due to their simple measurement of the optical path, rapid measurement, and non-contact accurate temperature measurement.

The method proposed in this paper is based on thermal imager to measure the optical absorption loss of thin films. The method proposed in this paper for measuring the optical absorption loss of a thin film based on a thermal imager is simpler than the existing method, and it can measure the absorption of thin films of optical elements in the laser. The addition of a reference sample in the test can reduce the impact of the changes of environmental temperature and the thermal imager noise on the temperature test results. Taking a certain area of the temperature field recorded by the thermal imager during the entire laser irradiation process can reduce the errors of the finite element simulation calculation caused by laser pointing fluctuations and the unsatisfactory spot distribution. The temperature change curve of the film during laser irradiation is obtained by a thermal imager, and the accurate absorption value of the film sample can be calculated through finite element simulation.

In this paper, a thermal imager was used to test the absorption loss of a small 45° high-reflection film. The absorption loss was 7.6 ppm, and the spatial distributions of the absorption loss of the same batch of large-size optical film samples were tested, the optical absorption was consistent. The absorption of the optical film measured by this method is consistent with the result of the laser calorimetry test. This method does not require long-term constant temperature and strict environmental temperature control, and the tested sample size is not limited.