The spectral responsivity scales of eighteen national standards laboratories have been compared within the wavelength range 250 nm to 1000 nm using two different types of silicon photodetector. Overall, good agreement was found between the scales of the participating laboratories, although some large deviations were also observed, especially in the ultraviolet.
A short-term effect of low-power ultraviolet (UV) radiation on the widely used Hamamatsu S1337 photodiode is investigated. Experiments show that such photodiodes exposed to 248 nm radiation exhibit a 0,6 % increase in responsivity at this wavelength, and a smaller increase at longer wavelengths. The increase is produced during the first tens of seconds of exposure and the new value reached by the responsivity remains stable even after further irradiation. The effect strongly depends on the wavelength of the radiation but is independent of power level within the measurement range of 8 W to 50 W. The surface reflectivity of the photodiode is not modified, indicating that radiation directly affects the internal quantum efficiency. It thus seems advisable to age this type of photodiode before calibration or simply to avoid any exposure to radiation below 300 nm.
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