We propose a space benchmark sensor with onboard SI (Système International) traceability by means of quantum optical radiometry. Correlated photon pairs generated by spontaneous parametric down-conversion (SPDC) in nonlinear crystals are used to calibrate the absolute responsivity of a solar observing radiometer. The calibration is systematic, insensitive to degradation and independent of external radiometric standards. Solar spectral irradiance at 380–2500 nm is traceable to the photon rate and Planck’s constant with an expected uncertainty of about 0.35%. The principle of SPDC calibration and a prototype design of the solar radiometer are introduced. The uncertainty budget is analyzed in consideration of errors arising from calibration and observation modes.

In this paper, the spatial properties of correlated photon in collinear phase-matching in the process of spontaneous parametric down conversion (SPDC) are researched. Based on the study of the phase-matching angle, non-collinear angle, and correlated photon wavelength, a theoretical model of non-collinear angular variation is derived, which can be used to estimate and predict the width of the correlated photon ring. The experimental measurement is carried out with CMOS camera, and the measurement results are consistent with the theoretical simulation results, which verifies the rationality of theoretical reasoning. Meanwhile, the change of the correlated photon divergence angle outside the crystal is studied, the closer the wavelength is to the degenerate, the smaller the measurement value of the divergence angle, which is agreement with the theoretical simulation. The results of the study play a reference role in the evaluation of the spatial properties of correlated photon and lay a foundation for the measurement of the correlated photon number rate and the calibration of a photodetector.

In order to establish a transferring chain from a photon flux of a single-photon source in quantum radiometry, the nonlinearity of the photodetector needs to be accurately measured. Using the flux superposition method, a nonlinearity measurement setup has been designed. The measurement setup consists of two tungsten halogen lamps, parent–child integrating spheres, an adjustable aperture, a diaphragm tube, and an optical filter. It has the advantage of low polarization error, low interference error, and low stray light effect. The Si photodiode to be measured is cooled to −40 °C to obtain a low noise level for low-flux radiation measurement. The nonlinearity of the Si photodetector is measured for photocurrent ranges from 10⁻¹² A~10⁻⁶ A level, with a relative standard uncertainty from 0.0092~0.023%. The relative standard uncertainty of the nonlinearity correction factor ranged from 0.023~0.049%.

Relative spectral responsivity is a basic parameter for detecting and evaluating the in-band response non-consistency of the channel polarization remote sensor (CPRS) in laboratory calibration. In this paper, a spectrally resolved calibration facility was assembled for the calibration of relative spectral responsivity by using novel supercontinuum laser and monochromator (SLM). Taking three polarization channels of 490 nm, 670 nm and 910 nm as examples, the relative spectral responsivity of the CPRS was obtained from two calibration sources, respectively – the SLM and the monochromatic light from SLM steered into integrating sphere. Before measuring the relative spectral responsivity of the CPRS, the degree of linear polarization (DOLP) and the polarization orientation angle of two calibration sources were acquired by the spectral polarization analyser (SPOLA). The test result indicates that the output light of the latter calibration source has less the DOLP and smaller range of variation in the polarization orientation angle. In the experiment of measuring the relative spectral responsivity, while using monochromator as calibration source, the in-band response non-consistency of the three channels were 0.91%, 4.25% and 1.06%, respectively. Correspondingly, while using monochromatic light steered into integrating sphere, there were 0.15%, 0.47% and 0.57%, respectively. It can be concluded that SLM equipped integrating sphere sharply decreased the impact from the polarization characteristic of the source and could be effectively applied in the relative spectral responsivity calibration of CPRS.

In order to meet the high uniformity calibration requirements for scientific-grade, large-size space detectors used in the CHES Extrasolar Planet Exploration Mission, this paper presents the design of a wide dynamic range, high uniformity spectral irradiance source (WHUIS). Utilizing a cascade integrating sphere design, and optimizing the overlapping area radiant flux adjustment structure and illumination light path, we achieve a wide dynamic range and high uniformity irradiance output. We established an irradiance transmission model based on the new assumption and analyzed the influence of factors such as illumination distance, stray light, and non-uniform radiance on the uniformity of irradiance output. The model is then validated by building experimental equipment. The findings show that in a circular area of 40 mm, the irradiance uniformity of our light source system exceeds 99.9%, and constant color temperature is adjustable within six orders of magnitude, consistent with the uniformity level predicted by the model.