Abstract
The Predictable Quantum Efficient Detector (PQED) is evaluated as a new primary standard of optical power. Design and characterization results are presented for a new compact room temperature PQED that consists of two custom-made induced junction photodiodes mounted in a wedged trap configuration. The detector assembly includes a window aligned in Brewster angle in front of the photodiodes for high transmission of p polarized light. The detector can also be operated without the window, 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 488 nm indicate that reflectance and internal quantum efficiency are consistent within 14 ppm and 10 ppm (ppm = part per million), respectively, and agree with the predicted values. The measured photocurrent ratio of the two photodiodes confirms the predicted value for s and p polarized light, and the spatial variation in the photocurrent ratio can be used to estimate the uniformity in the thickness of the silicon dioxide layer on the surface of the photodiodes. In addition, the spatial non-uniformity of the responsivity of the PQED is an order of magnitude lower than that of single photodiodes. Such data provide evidence that the room temperature PQED may replace the cryogenic radiometer as a primary standard of optical power in the visible wavelength range.
Highlights
Cryogenic electrical substitution radiometers [1,2,3,4] are currently used as the primary standard of optical power
In practice, the responsivity of a photodetector is reduced by reflectance and the internal quantum deficiency (IQD), corresponding to the relative number of absorbed photons not producing a collected charge carrier
A new compact size room temperature Predictable Quantum Efficient Detector (PQED) was designed, consisting of two custom designed induced junction photodiodes mounted in a wedged light-trapping configuration
Summary
Cryogenic electrical substitution radiometers [1,2,3,4] are currently used as the primary standard of optical power. The effect of reflectance, on the other hand, can be reduced by Brewster-angle operation [13] or by assembling the photodiodes into a lighttrapping configuration [9,14,15,16,17] These loss reduction methods are used to construct the Predictable Quantum Efficient Detector (PQED) [18,19]. It consists of two induced junction photodiodes with tailored design parameters suitable for the particular light-trapping configuration. The uncertainty of the predicted responsivity of the room temperature PQED is comparable with that of the cryogenic radiometer suggesting that the PQED can be used as a primary standard of optical power in the visible wavelength range. With the exception of stainless steel bellows, the body of the detector is made of black anodized aluminum
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