A primary standard of optical power based on induced-junction silicon photodiodes operated at room temperature

We present the design and construction of a new compact room temperature predictable quantum efficient detector (PQED). It consists of two custom-made induced-junction photodiodes mounted in a wedge trap configuration and a window aligned at Brewster's angle for high transmission of p polarized light. The window can also be removed, in which case a dry nitrogen flow system is utilized to prevent dust contamination of the photodiodes. Measurements of individual detectors at the wavelength of 488nm indicate that reflectance and spectral responsivity are consistent within 4ppm and 13ppm peak-to-peak variation, respectively, and agree with the predicted values. The spatial non-uniformity of the responsivity of the PQED is an order of magnitude lower than that of single photodiodes. The internal quantum efficiency of the photodiodes is concluded to be spatially uniform within 50ppm. These measurement results - together with the responsivity predictable by fundamental laws of physics - provide evidence that the room temperature PQED may replace the cryogenic radiometer as a primary standard of optical power in the visible wavelength range of 380nm to 780nm.