Laser-based primary standard for absolute spectral irradiance calibration with predictable quantum efficient detectors

State-of-the-art spectral solar irradiance measurements are performed using spectroradiometers, devices that require regular laboratory calibration for traceability to the SI. Typically, these calibrations involve transfer standard light sources, calibrated at National Metrology Institutes against primary standards. However, these transfer standards have disadvantages, and their uncertainties are significantly higher than primary optical standards. In this study, we suggest a novel optical facility for spectroradiometer calibration of spectral responsivity based on predictable quantum efficient detector (PQED) and an ultra-stable, homogeneous monochromatic light beam. This approach is a proof-of-concept for a cost-effective, in-lab primary standard alternative based spectral irradiance facility with significantly reduced uncertainties than the traditional calibration methods. The performance of the system was evaluated at two laser wavelengths, 473 nm and 633 nm using three spectroradiometers calibrated with standard tungsten halogen lamps traceable to the SI. The relative difference in measured irradiances obtained with both methods was consistently below 0.8%, which is well within the combined uncertainties attributed to state-of-the-art spectroradiometer calibration methods. We suggest that combining the PQED with a temporally stable and spatially homogeneous monochromatic light beam can provide a system useable as a primary reference of spectral irradiance in the 400 nm–800 nm spectral range, directly in-lab, significantly shortening the traceability chain to the SI.