The establishment of the NPL infrared relative spectral responsivity scale using cavity pyroelectric detectors

The establishment of a relative spectral responsivity scale requires the availability of a detector with a relative spectral responsivity which can be measured or estimated. NPL has addressed this requirement by designing a new detector with a measurable relative spectral response profile in the 800 nm to 24 µm wavelength range. The new detector is based on a large area pyroelectric detector enclosed in a removable gold-coated hemispherical reflector. A number of these cavity pyroelectric detectors were fabricated and three have been selected and are currently being used as the primary standards for the establishment of the NPL relative spectral responsivity scale in the infrared region. This paper summarizes the design and performance characteristics of these cavity pyroelectric detectors and demonstrates how they are used to establish the NPL relative spectral responsivity scales in the 0.8 µm to 24 µm wavelength range.