Predictable quantum efficient detector: II. Characterization and confirmed responsivity

Abstract

The predictable quantum efficient detector (PQED) is intended to become a new primary standard for radiant power measurements in the wavelength range from 400 nm to 800 nm. Characterization results of custom-made single induced junction photodiodes as they are used in the PQED and of assembled PQEDs are presented. The single photodiodes were tested in terms of linearity and spatial uniformity of the spectral responsivity. The highly uniform photodiodes were proved to be linear over seven orders of magnitude, i.e. in the radiant power range from 100 pW to 400 µW. The assembled PQED has been compared with a cryogenic electrical substitution radiometer with a very low uncertainty of the order of 30 ppm. Experimental results show good agreement with the modelled response of the PQED to optical radiation and prove a near unity external quantum efficiency.

Primary standard of optical power operating at room temperature

“…Measurements against cryogenic radiometers at 476 nm, 532 nm and 760 nm confirm the predicted responsivity [19]. 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.…”

“…The data indicate that with a 1/e 2 laser beam diameter of 1.2 mm, the responsivity changed only 50 ppm within a diameter of 4 mm. Thus, the non-uniformity of the PQED is about ten times lower than the non-uniformity of single induced junction photodiodes over similar area, as measured in [19], and can match that of best conventional silicon trap detectors [20][21][22]. …”

“…The type of induced junction photodiodes used in the new detector design are described and characterized in [18] and [19]. In these photodiodes the depletion region is produced by the surface charges in the silicon dioxide layer [10], which improves the collection efficiency of charge carriers.…”

“…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.…”

Advantages of white LED lamps and new detector technology in photometry

“…The method relies on an unfiltered detector with a known absolute responsivity and on carrying out the photometric weighting numerically based on the measured relative spectrum of the light source, thus eliminating the need of using photometric filters in the unit realization. When the predictable quantum efficient detector (PQED) 17,18,19 -a new primary standard for optical power that is based on an induced junction photodiode trap and that has a near unity quantum efficiency -is used as the broadband detector, high accuracy can be achieved, because the absolute spectral responsivity of the PQED can be predicted with a relative uncertainty of less than 0.01% 20,21 . We will demonstrate that the PQED method is more accurate than the photometer method when white LED lamps are used as light sources.…”