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Proceedings Paper

Design of a cryogenic absolute prism refractometer for infrared optical materials
Author(s): Sheng Liao; Lei Ni; Qi-feng Ren
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Paper Abstract

In order to enable high quality infrared lens designs at cryogenic temperature, we decided to study the IR materials’ optical properties, such as the refractive index, the thermo-optic coefficient (dn/dT) etc. As a matter of fact, accurate precision refractive index data for infrared optical materials at cryogenic temperatures is scarce, so we decided to design a cryogenic absolute prism refractometer for infrared optical materials. Considering the most accurate and precise measurements of the real part of the refractive index, n, optical materials are obtained through minimum deviation refractometry, we decided to choose this classic refractometer for our cryogenic IR materials index measuring. Given the thermo-optic coefficient of many IR materials, which was reported by NASA, the measurement precision is at least 10-3. In order to achieve this precision, the error of apex angle of sample prism and deviation angle must be less than 20 arc-second. The thermal stress of the prism must be in control, or the volume change of the prism may lead to stress birefringence (photo-elastic effect). The bandwidth of IR source must be less than 20nm and the error caused by dispersion (dn/dλ) will generally be negligible in our system. The hardware system consists of 5 subsystems: the rotating sample chamber subsystem, the rotating plat mirror subsystem, the cryogenic vacuum subsystem, auto control subsystem, exit image collimation subsystem. Finally, the system is designed to measure IR materials’ indices between 1-4, at the wavelength of 1.0-12μm, at room (300K) and cryogenic temperature (100K), with a precision of 10-4.

Paper Details

Date Published: 16 November 2011
PDF: 8 pages
Proc. SPIE 8321, Seventh International Symposium on Precision Engineering Measurements and Instrumentation, 832117 (16 November 2011); doi: 10.1117/12.904003
Show Author Affiliations
Sheng Liao, Institute of Optics and Electronics (China)
Lei Ni, Institute of Optics and Electronics (China)
Graduate School of Chinese Academic of Science (China)
Qi-feng Ren, Institute of Optics and Electronics (China)


Published in SPIE Proceedings Vol. 8321:
Seventh International Symposium on Precision Engineering Measurements and Instrumentation
Kuang-Chao Fan; Man Song; Rong-Sheng Lu, Editor(s)

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