Accurate determination of the spectral responsivity of silicon trap detectors between 238 nm and 1015 nm using a laser-based cryogenic radiometer

The Physikalisch-Technische Bundesanstalt has further improved and extended its spectral responsivity scale based on the laser-operated radiation ther mometry cryogenic radiometer. Five laser wavelengths in the ultraviolet (UV ) (238 nm to 400 nm) and another fifteen in the visible and near-infrared ( NIR) (400 nm to 1015 nm) almost cover the entire spectral range where silic on photodiodes can be used in air. The lasers employed are a Kr+ laser, an Ar+ laser with optional intra-cavity frequency-doubling, and a continuously tuneable Ti:sapphire ring laser. The total relative standard uncertainty o f the spectral responsivity at the laser lines is u = 10(-4) in the visible and NIR below 950 nm and u = 10(-3) in the W. With an improved model for i nterpolation between the laser wavelengths, a continuous scale of spectral responsivity has been established in the wavelength range 400 nm to 1015 nm .