An Assessment of the Ageing of the Absolute Spectral Responsivity of Trap Detectors at Krypton Ion Laser Emission Wavelengths

We have assessed the absolute spectral responsivities of three-element trap detectors calibrated against the NPL primary standard cryogenic radiometer at eight krypton ion laser emission wavelengths over an approximate period of twenty-years. As expected, we observed that the absolute spectral responsivities decrease with time. Additionally, we found that as the wavelength decreases, the ageing rate increases. At 356.4 nm, an average responsivity decrease of around -1800 ppm/year is reported. While at longer wavelengths, the slowest rate of ageing, approximately 40 ppm/year, occurs at 799.3 nm. Interestingly, the year-on-year changes exhibit a relatively linear trend, allowing us to predict the future performance of the trap detectors. It is important to note, however, that predicted performance cannot be guaranteed and regular recalibration against a primary standard is essential, especially if low calibration uncertainties are required.