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 National Physical Laboratory primary standard cryogenic radiometer at eight krypton ion laser emission wavelengths over an approximate period of 20 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 yr-1 is reported. While at longer wavelengths, the slowest rate of ageing, approximately -40 ppm yr-1, 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.