04.01.2012
Figure 1: Predictable Quantum Efficient Detector – PQED
In the past three years, the European iMERA-Plus research project "Candela: Towards quantum-based photon standards" (
www.quantumcandela.org) has been focused on the further development of both, the classical radiometry and the radiometry of a few photons and the linkage of both. For this purpose, a calculable, high-efficiency radiation detector was developed on the basis of special silicon photodiodes (Predictable Quantum Efficient Detector – PQED). In this connection, PTB's Working Group "Detector Radiometry" had taken over the comprehensive electro-optical characterization and the high-precision determination of the quantum efficiency of this novel detector in order to check the physical model for the prediction of the quantum efficiency of the PQED which had been developed within the scope of the research project. This is an important prerequisite for its use as a compact primary standard for optical radiant power.
The quantum efficiency of the PQED was determined at two wavelengths (758 nm and 532 nm), at ambient temperature, at the temperature of liquid nitrogen (-196 °C) and as a function of the bias voltage applied with an uncertainty of only 30 ppm. For that purpose, a primary standard for optical radiant power based on the electrical substitution principle - a so-called cryogenic radiometer - was used.
The measurements carried out within the scope of the research project showed a quantum efficiency of the PQED of more than 99.99% at a wavelength of 532 nm. The prediction of the physical model for ambient temperature conditions could thus be confirmed. The extensive investigations at -196 °C have, in addition, furnished details for the improvement of the model for the description of the temperature dependence. Due to these positive results, the investigations regarding suitability of the PQED as a primary standard for optical radiant power will be continued by the project partners.
Contact:
L. Werner, 7.33, e-mail: 
Lutz.Werner(at)ptb.de