ECAMP 15

CMOS sensors, typically used in smartphone cameras and other commercial applications, have gained recent attention for their potential use in astronomical [1] and biological [2,3] x-ray imaging due to their improved readout speed and resolution, and lower power consumption, noise, and cost compared to their CCD counterparts. This work explores the conversion of two commercial off the shelf CMOS cameras into soft x-ray (SXR) detectors; investigating their spectral resolution, optimizing their sensitivity, and implementing them as laser produced plasma imaging devices.
A Sony IMX477 and a Sony IMX178 were adapted by removal of their glass windows and addition of a free standing 1.4 μm Al filter. Each sensor was spectrally calibrated using known well-defined emission structures of Fe-Zn plasmas in the 600-1200 eV region. In both cases, a linear relationship between photon energy and detected counts was quantified, and with E/ΔE > 15.
We also investigated methods of improving the SXR detection efficiency of the IMX477 detector, particularly in the >600 eV region, by removing polymer layers on the sensor surface, and by thinning the Al filter. The removal of the Bayer layer and microlens array resulted in a 50% increase in sensitivity, but introduced significant non-uniformity. The Al filter was then deposited directly on the CMOS sensor with a thickness of 100 nm through thermal evaporation to extend the spectral sensitivity from 600 eV down to ~300 eV.
The work has enhanced our understanding of the behaviour of these cost-effective soft x-ray detectors, although there are still aspects to be explored. We intend to use these sensors in order to spatially map the density of laser plasmas by using soft x-rays as a backlight.

[1] Ogino, Naoki, et al. "Performance Verification of Next-Generation Si CMOS Soft X-ray Detector for Space Applications." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, vol. 987, 2021, article no. 164843.
[2] Alcalde Bessia, Fabricio, et al. "X‐ray micrographic imaging system based on COTS CMOS sensors." International Journal of Circuit Theory and Applications, vol. 46.10, 2018, pp. 1848-1857.
[3] Miguel Sofo Haro, et al. “Soft X-rays spectroscopy with a commercial CMOS image sensor at room temperature.” Radiation Physics and Chemistry, Vol. 167, 2020, 108354.