Calibrating CMOS Detectors for Scientific Measurement

Solar physicists study the hot plasma, waves, magnetic fields, and energy release of solar flares by imaging them in x-ray and extracting data from those images. The digital image sensors that are used today—called CCD (charged coupled device)—have major limitations in imaging solar flares. Solar flares’ soft x-ray and EUV emission varies in intensity along magnetic loops and varies over short time frames. Current CCD imager pixels readout is sequential through a single amplifier (gain) resulting in relatively slow readout speeds. Thus during solar flares, CCD suffer from saturation and blooming. Because of this, CCD images of solar flares often contain very little usable data. To avoid this we can use CMOS (complementary metal oxide semiconductor) detectors, which have signal amplification on each pixel and parallel column readout, resulting in 10-100s times faster performance than CCD. Hence CMOS will mitigate saturation and blooming. The ultimate goal of this project is to develop processing software to determine the gain per individual pixel for any CMOS device given a CMOS measurement and a known source flux. The first step to achieve this goal during the summer of 2020 I simulated a CCD detector signal with a predefined illumination of monoenergetic photons.This included a fixed signal offset (signal bias), random noise (gaussian distribution), and fixed gain across all pixels. I created a histogram with the charge values of each pixel and fit two gaussian curves to the histogram data (one to the bias curve and one to the signal curve). The gain can be determined by fitting the gaussian amplitude, centroid, and standard deviation. Further improvements to the code will help future researchers characterize CMOS detectors, operate them on space observatories, and better capture dynamic phenomena in solar flares.NSF-REU solar physics program at SAO, grant number AGS-185075