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Realization of a primary irradiance scale for solar irradiance measurements based on a predictable quantum efficient detector and a quasi-monochromatic portable tunable source

Year: 2026
Type: article
Abstract: Long-term solar ultraviolet (UV) monitoring for climate modeling and ozone trend assessment demands exceptionally low measurement uncertainties. Traditional lamp-based radiometric calibrations using standard FEL lamps suffer from high intrinsic uncertainties in the UV region and are highly susceptible to drift over time. To address this gap, this work presents a primary, detector-based irradiance scale for solar UV measurements covering the 350 nm to 550 nm spectral range of the QASUME reference solar spectroradiometer. The proposed scale relies on a predictable quantum efficient detector (PQED) built with self-induced silicon photodiodes in a trap configuration. While PQEDs naturally exhibit near-unitary internal quantum efficiency between 450 nm and 850 nm, their extension into the UV requires accounting for impact ionization via an enhanced Quantum Yield effect. By implementing a validated quantum Yield model experimentally verified against the cryogenic radiometer primary standard at the Czech Metrology Institute (CMI), the scale achieves an estimated primary irradiance standard uncertainty of 0.28% in the near-UV range (350–425 nm) and 0.20% at wavelengths longer than 425 nm, which is a factor of 2 improvement compared to the current source-based scale. The realization of the detector-based scale is based on a transportable tunable light source (TuPS) alongside an automated comparison facility comprising a PQED as the primary irradiance reference, establishing an in-situ, highly accurate traceability chain for the QASUME reference spectroradiometer.
DOI: 10.1364/oe.607165
Language: English
Open Access status: gold
Estimated APC paid: $2,270
OpenAlex ID: W7170052523
FWCI:
Cites: 10
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Related to: 10