Fig. 1: Absorption and contrast difference at different wavelengths, measured on liver cells.

a Conceptual “hockey stick” figure of tissue absorption as observed in many biological materials^10,11,12,13. b Measured contrast (standard deviation over median) at different wavelengths in brightfield microscopy of liver cells. c Schematic diagram of light interacting with liver cells containing nano-sized fenestrations present on the cell membrane (shown in dark circles). In the UVC, both the real refractive index and the extinction coefficient leave an appreciable imprint on the probing light. A phase retrieval algorithm can disentangle the real and imaginary parts from intensity images in a quantitative manner¹⁴