Initial Characterization of Back-Illuminated CMOS Detector Noise

During periods of high solar activity, solar flares tend to occur in coronal active regions, heating the local plasma to temperatures above 10 MK. As a result, an abundant amount of soft x-rays (SXR) and extreme ultraviolet (EUV) are emitted from the hot plasma. While SXR is a good source for imaging solar activity due to its highly contrasting details, this can be a problem for current EUV and SXR CCD imagers on solar observatories. When large flares are observed, the CCD pixels can saturate and bloom into adjacent pixels, resulting in a tremendous loss in critical flare dynamic information (flaring plasma geometry, participle acceleration, etc.). We present the use of silicon-based SXR CMOS detectors with readout rates faster than 10 Hz. We characterize the various CMOS noise as a function of readout rates to quantify measurement precision, imaging contrast, and spectral resolution. We measure and analyze SXR data inside and outside of a vacuum chamber. We characterize the effects of readout noise, dark current, and other background noise contributions in the SXR data. Initial results demonstrate that variation in individual pixel noise across multiple frames tends toward a normal distribution. After conducting mean and median frame subtraction, the average noise from all pixels conforms to a singular normal distribution. In the future, data will be collected at various temperatures to look at how pixel noise distributions change. With further work, we aim to utilize the faster readout rates in CMOS detectors on future solar physics space missions. This work is supported by the NSF-REU solar physics program at SAO, grant number AGS-1850750.