Fig. 3: Spatial resolution of the probe.

a x–z cross-section extracted from the reconstructed 3D photoacoustic image of a multi-layer ribbon phantom showing the individual absorbing ribbons over the probe field of view; the apparent curvature of the features in the top three rows is not an image artifact but reflects the true geometry of the phantom. b, c Lateral and vertical profiles (blue filled circles), respectively, through the highlighted feature in a; The lateral resolution is given by the FWHM of a Gaussian function that is fitted to the derivative of the falling edge (orange line in b). The vertical resolution is given by the FWHM of a Gaussian function that is fitted (orange line in c) to the vertical profile. d A contour plot that shows the variation in the lateral spatial resolution over the x–z plane. Incident fluence: 18 mJ/cm²