The National Reference Reflectometer has been developed by the National Physical Laboratory (NPL) to realize scales for radiance factor and total diffuse reflectance, the latter scale being obtained through the spatial integration of goniometric measurements of reflectance. Analysis of its performance in the spectral region from 400 nm to 1000 nm shows that for spectrally neutral white materials such as matte white tiles and Spectralon™ plaques the instrument is capable of realizing 0/45 radiance factor measurements with an uncertainty of 0.2% (k = 2) and 0/d total diffuse reflectance measurements with an uncertainty of approximately 0.25% (k = 2). The uncertainties depend on the variation of reflectance with angle, and there will therefore be some dependence on the material being measured. This instrument is now used to establish UK diffuse reflectance scales in the visible part of the spectrum.

No 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.

The APMP.PR-S4 comparison of fiber optic power responsivity and nonlinearity at 1550 nm, from 1 mW to 250 mW, was carried out. In total three institutes participated: NMIJ (Japan), PTB (Germany) and NPL (United Kingdom). The measurements started in December 2008 and ended in December 2009.For fiber optic power responsivity, all participants reported their results and all results were used for the intercomparison: no measurement was subject to rejection. For nonlinearity two participants reported their results, therefore only a bilateral comparison was performed.The analysis method was carried out according to the Guidelines for CCPR Comparison Report Preparation and has been accepted by all participants. The reference value of fiber optic power responsivity was calculated using all participants' results. For fiber optic power from 10 mW to 250 mW all participants had unilateral DoE values consistent with their uncertainties at the k = 2 level. For fiber optic power of 1 mW all participants achieved consistency at the k = 3 level. For nonlinearity, the consistency of the measurements at both NMIJ and PTB was achieved with uncertainty at the k = 2 level.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the APMP, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

No abstract