Effect of polytetrafluoroethylene (PTFE) phase transition at 19°C on the use of Spectralon as a reference standard for reflectance

Abstract

Sintered polytetrafluoroethylene (PTFE) is highly reflective and is widely used as a reference standard in remote sensing, radiometry, and spectroscopy. The relative change in output flux from a PTFE integrating sphere over the room temperature phase transition at 19°C has been measured at a monochromatic wavelength of 633 nm as 1.82±0.21%. The change in output flux was attributed to a small change of 0.09±0.02% in the total hemispherical reflectance of PTFE, caused by a change in its material density as a result of the phase transition. For the majority of users, this small change measured in total hemispherical reflectance is unlikely to impact significantly the accuracy of PTFE flat panel reflectors used as reference standards. However, owing to the multiple reflections that occur inside an integrating sphere cavity, the effect is multiplied and remedial action should be applied, either via a mathematical correction or through temperature stabilization of the integrating sphere when high accuracy (<5%) measurements of flux, irradiance, or radiance are required from PTFE-based integrating spheres at temperatures close to the phase transition at 19°C.

Electret Modulation Strategy to Enhance the Photosensitivity Performance of Two-Dimensional Molybdenum Sulfide

“…The decrease in absorptance of PTFE/MoS 2 may be caused by the reflection of the PTFE film. 44 The band gap of the MoS 2 products was derived from the Tauc plot, implying a direct band gap of 2.42 eV. 45 Position-dependent Raman spectroscopy (Figure 2c) was performed under 532 nm laser excitation for a deep understanding of the PTFE effect on MoS 2 nanosheets.…”

“…Figure b compares the UV–vis-NIR absorption spectra of MoS 2 nanosheets and PTFE/MoS 2 samples (located on SiO 2 /Si substrates), showing similar absorption edges. The decrease in absorptance of PTFE/MoS 2 may be caused by the reflection of the PTFE film . The band gap of the MoS 2 products was derived from the Tauc plot, implying a direct band gap of 2.42 eV .…”

Hemispherical-Directional Reflectance (HDRF) of Windblown Snow-Covered Arctic Tundra at Large Solar Zenith Angles

“…The radiance reflected by the Spectralon panel was subject to correction by the intercalibration correction factor C f derived in Section III-D2, when applied to each of the individual foreoptics. Temperature differences between ambient laboratory and field conditions were considered unlikely to significantly affect the reflectance of the Spectralon reference standard [31].…”

Characterisation of the HDRF (as a proxy for BRDF) of snow surfaces at Dome C, Antarctica, for the inter-calibration and inter-comparison of satellite optical data

“…This deviation of the Spectralon panel from Lambertian is not specifically accounted for in the data analysis. Spectralon panels are typically calibrated at room temperature, Ball et al (2013) showed that there was no significant difference between measurements taken at room temperature (~20°C) and at polar temperatures despite a phase transition in the panels at 19°C.…”