Ball, C P; Levick, A P; Woolliams, E R; Green, P D; Dury, M R; Winkler, R; Deadman, A J; Fox, N P; King, M D* (2013) Effects of the polytetrafluoroethylene (PTFE) phase transition at 19 °C on the use of Spectralon as a reference standard for reflectance. Appl. Opt., 52 (20). pp. 4806-4812.

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Abstract

Sintered polytetrafluroethylene (PTFE) or SpectralonTM is highly reflective and is widely used as a reference standard for reflectance in remote sensing, radiometry and spectroscopy. The change in radiance from a PTFE coated integrating sphere during the phase transition at 19 °C has been measured at a wavelength of 633 nm as 1.78 % ± 0.02 %. The change in radiance due to the thermal expansion of the PTFE sphere was calculated using published coefficients of thermal expansion for sintered PTFE and was found to contribute 0.30 % to the total change in sphere radiance. The remaining 1.48 % was attributed to a small change of 0.08 % ± 0.01 % in the total hemispherical reflectance of PTFE. The effect of the phase transition does not significantly impact upon the accuracy of PTFE reference standards for reflectance. However, owing to the multiple reflections that occur inside an integrating sphere's cavity, and the additional effect of thermal expansion on the sphere, a downward correction may be necessary when measurements of radiance or irradiance are required from PTFE based integrating spheres at temperatures below 19 °C.

Item Type:	Article
Keywords:	spectralon, reflectance, radiance, transmittance
Subjects:	Optical Radiation and Photonics Optical Radiation and Photonics > Environment and Climate Change
Identification number/DOI:	10.1364/AO.52.004806
Last Modified:	02 Feb 2018 13:14
URI:	https://eprintspublications.npl.co.uk/id/eprint/5879