Thermopile detectors: spatial non-uniformity measurements and correction methods

The spatial non-uniformity of a newly developed electrically calibrated radiometer system is characterized. The detector is a thin-film thermopile with an integral electrical heater. This paper shows that the local responsivities of these detectors have a rotational symmetry and a quadratic dependence on the distance to the centre of the detector. Typical measurement errors, which can be caused by applying different beam sizes, different power distributions of the beams, and different beam positions impinging on the detector, are investigated. A significant reduction of measurement uncertainties is achieved using specific corrections. The influence of spatial non-uniformity on responsivity measurements is experimentally checked with various types of beam.